Production of primordial black holes in improved E-models of inflation

Published Paper #: 1135

Authors:, Daniel Frolovsky, Sergei V. Ketov,

Journal: Universe 2023, 9(6), 294

url: http://arxiv.org/pdf/2304.12558v3.pdf

Abstract: The E-type $\alpha$-attractor models of single-field inflation were generalized further in order to accommodate production of primordial black holes (PBH) via adding a near-inflection point to the inflaton scalar potential at smaller scales, in good agreement with measurements of the cosmic microwave background (CMB) radiation. A minimal number of new parameters was used but their fine-tuning was maximized in order to increase possible masses of PBH formed during an ultra-slow-roll phase leading to a large enhancement of the power spectrum of scalar (curvature) perturbations by 6 or 7 orders of magnitude against the power spectrum of perturbations observed in CMB. It was found that extreme fine-tuning of the parameters in our models can lead to a formation of Moon-size PBH with the masses of approximately $10^{26}$ g, still in agreement with CMB observations. Quantum corrections are known to lead to the perturbative upper bound on the amplitude of large scalar perturbations responsible for PBH production. The quantum (one-loop) corrections in our models were found to be suppressed by one order of magnitude for PBH with the masses of approximately $10^{19}$ g, which may form the whole dark matter in the Universe.

Keywords: PBH_formation, Inflation_model, CMB_ns
Comment : Big claim is : n_s is consistent with CMB, which is possible in principle because they are looking with a particular E-$\alpha$ attractor model with certain fexibility, but I am not very sure if they are verifying their statement with full phased numerical analysis or semi slow-roll only exact background evolution kind of analysis.
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Primordial black holes and induced gravitational waves from double-pole   inflation

Published Paper #: 1134

Authors:, Chengjie Fu, Shao-Jiang Wang,

Journal: JCAP 06 (2023) 012

url: http://arxiv.org/pdf/2211.03523v2.pdf

Abstract: The primordial black hole (PBH) productions from the inflationary potential with an inflection point usually rely heavily on the fine-tuning of the model parameters. We propose in this work a new kind of the $\alpha$-attractor inflation with asymmetric double poles that naturally and easily lead to a period of non-attractor inflation, during which the PBH productions are guaranteed with less fine-tuning the model parameters. This double-pole inflation can be tested against the observational data in the future with rich phenomenological signatures: (1) the enhanced curvature perturbations at small scales admit a distinctive feature of ultraviolet oscillations in the power spectrum; (2) the quasi-monochromatic mass function of the produced PBHs can be made compatible to the asteroid-mass PBHs as the dominant dark matter component, the planet-mass PBHs as the OGLE ultrashort-timescale microlensing events, and the solar-mass PBHs as the LIGO-Virgo events; (3) the induced gravitational waves can be detected by the gravitational-wave detectors in space and Pulsar Timing Array/Square Kilometer Array.

Keywords: ::

Signatures of a High Temperature QCD Transition in the Early Universe

Published Paper #: 1133

Authors:, Philip Lu, Volodymyr Takhistov, George M. Fuller,

Journal: Phys. Rev. Lett. 130 (2023) 22, 221002

url: http://arxiv.org/pdf/2212.00156v2.pdf

Abstract: Beyond Standard Model extensions of QCD could result in quark and gluon confinement occurring well above a temperature of $\sim$GeV. These models can also alter the order of the QCD phase transition. The enhanced production of primordial black holes (PBHs) that can accompany the change in relativistic degrees of freedom at the QCD transition therefore could favor the production of PBHs with mass scales smaller than the Standard Model QCD horizon scale. Consequently, and unlike PBHs associated with a standard GeV-scale QCD transition, such PBHs can account for all the dark matter abundance in the unconstrained asteroid-mass window. This links beyond Standard Model modifications of QCD physics over a broad range of unexplored temperature regimes ($\sim 10-10^3$ TeV) with microlensing surveys searching for PBHs. Additionally, we discuss implications of these models for gravitational wave experiments. We show that a first order QCD phase transition at $\sim7$ TeV is consistent with the Subaru Hyper-Suprime Cam candidate event, while a $\sim 70$ GeV transition is consistent with OGLE candidate events, and also could account for the claimed NANOGrav gravitational wave signal.

Keywords: ::

Primordial black hole isocurvature modes from non-Gaussianity

Published Paper #: 1132

Authors:, Raphaël van Laak, Sam Young,

Journal: JCAP05(2023)058

url: http://arxiv.org/pdf/2303.05248v2.pdf

Abstract: Primordial black holes (PBHs) are black holes that might have formed in high density regions in the early universe. The presence of local-type non-Gaussianity can lead to large-scale fluctuations in the PBH formation rate. If PBHs make up a non-negligible fraction of dark matter, these fluctuations can appear as isocurvature modes, and be used to constrain the amplitude of non-Gaussianity. Assuming that the parameters of non-Gaussianity are constant over all scales, we build upon the results of previous work by extending the calculation to include peaks theory and making use of the compaction $C$ for the formation criteria, accounting for non-linearities between $C$ and the curvature perturbation $\zeta$. For quadratic models of non-Gaussianity, our updated calculation gives constraints that are largely unaltered compared to those previously found, while for cubic models the constraints worsen significantly. In case all of the DM is made up of PBHs, the parameters of non-Gaussianity are $-2.9\cdot10^{-4}<f<3.8\cdot10^{-4}$ and $-1.5\cdot10^{-3}<g<1.9\cdot10^{-3}$ for quadratic and cubic models respectively.

Keywords: ::

Constraints on primordial black holes from observation of stars in dwarf   galaxies

Published Paper #: 1131

Authors:, Nicolas Esser, Peter Tinyakov,

Journal: Phys. Rev. D 107, 103052 (2023)

url: http://arxiv.org/pdf/2207.07412v2.pdf

Abstract: We propose a way to constrain the primordial black hole (PBH) abundance in the range of PBH masses $m$ around $10^{20}$g based on their capture by Sun-like stars in dwarf galaxies, with subsequent star destruction. We calculate numerically the probability of a PBH capture by a star at the time of its formation in an environment typical of dwarf galaxies. Requiring that no more than a fraction $\xi$ of stars in a dwarf galaxy is destroyed by PBHs translates into an upper limit on the PBH abundance. For the parameters of Triangulum II and $\xi=0.5$, we find that no more than $\sim 35\%$ of dark matter can consist of PBHs in the mass range $10^{18} - \text{(a few)}\times 10^{21}$g. The constraints depend strongly on the parameter $\xi$ and may significantly improve if smaller values of $\xi$ are established from observations. An accurate determination of $\xi$ from dwarf galaxy modeling is thus of major importance.

Keywords: ::

Primordial black holes and gravitational waves induced by   exponential-tailed perturbations

Published Paper #: 1130

Authors:, Katsuya T. Abe, Ryoto Inui, Yuichiro Tada, Shuichiro Yokoyama,

Journal: JCAP05 (2023) 044

url: http://arxiv.org/pdf/2209.13891v2.pdf

Abstract: Primordial black holes (PBHs) whose masses are in $\sim[10^{-15}M_\odot,10^{-11}M_{\odot}]$ have been extensively studied as a candidate of whole dark matter (DM). One of the probes to test such a PBH-DM scenario is scalar-induced stochastic gravitational waves (GWs) accompanied with the enhanced primordial fluctuations to form the PBHs with frequency peaked in the mHz band being targeted by the LISA mission. In order to utilize the stochastic GWs for checking the PBH-DM scenario, it needs to exactly relate the PBH abundance and the amplitude of the GWs spectrum. Recently in Kitajima et al., the impact of the non-Gaussianity of the enhanced primordial curvature perturbations on the PBH abundance has been investigated based on the peak theory, and they found that a specific non-Gaussian feature called the exponential tail significantly increases the PBH abundance compared with the Gaussian case. In this work, we investigate the spectrum of the induced stochastic GWs associated with PBH DM in the exponential-tail case. In order to take into account the non-Gaussianity properly, we employ the diagrammatic approach for the calculation of the spectrum. We find that the amplitude of the stochastic GW spectrum is slightly lower than the one for the Gaussian case, but it can still be detectable with the LISA sensitivity. We also find that the non-Gaussian contribution can appear on the high-frequency side through their complicated momentum configurations. Although this feature emerges under the LISA sensitivity, it might be possible to obtain information about the non-Gaussianity from GW observation with a deeper sensitivity such as the DECIGO mission.

Keywords: ::

No constraints for $f(T)$ gravity from gravitational waves induced from   primordial black hole fluctuations

Published Paper #: 1129

Authors:, Theodoros Papanikolaou, Charalampos Tzerefos, Spyros Basilakos, Emmanuel N. Saridakis,

Journal: Eur.Phys.J.C 83 (2023)

url: http://arxiv.org/pdf/2205.06094v2.pdf

Abstract: Primordial black hole (PBH) fluctuations can induce a stochastic gravitational wave background at second order, and since this procedure is sensitive to the underlying gravitational theory it can be used as a novel tool to test general relativity and extract constraints on possible modified gravity deviations. We apply this formalism in the framework of $f(T)$ gravity, considering three viable mono-parametric models. In particular, we investigate the induced modifications at the level of the gravitational-wave source, which is encoded in terms of the power spectrum of the PBH gravitational potential, as well as at the level of their propagation, described in terms of the Green function which quantifies the propagator of the tensor perturbations. We find that, within the observationally allowed range of the $f(T)$ model-parameters, the obtained deviations from general relativity, both at the levels of source and propagation, are practically negligible. Hence, we conclude that realistic and viable $f(T)$ theories can safely pass the primordial black hole constraints, which may offer an additional argument in their favor.

Keywords: ::

Distinct signatures of spinning PBH domination and evaporation: doubly   peaked gravitational waves, dark relics and CMB complementarity

Published Paper #: 1128

Authors:, Nilanjandev Bhaumik, Anish Ghoshal, Rajeev Kumar Jain, Marek Lewicki,

Journal: JHEP 05 (2023) 169

url: http://arxiv.org/pdf/2212.00775v2.pdf

Abstract: Ultra-low mass primordial black holes (PBH), which may briefly dominate the energy density of the universe but completely evaporate before the big bang nucleosynthesis (BBN), can lead to interesting observable signatures. In our previous work, we studied the generation of a doubly peaked spectrum of induced stochastic gravitational wave background (ISGWB) for such a scenario and explored the possibility of probing a class of baryogenesis models wherein the emission of massive unstable particles from the PBH evaporation and their subsequent decay contributes to the matter-antimatter asymmetry. In this work, we extend the scope of our earlier work by including spinning PBHs and consider the emission of light relativistic dark sector particles, which contribute to the dark radiation (DR) and massive stable dark sector particles, thereby accounting for the dark matter (DM) component of the universe. The ISGWB can probe the non-thermal production of these heavy DM particles, which cannot be accessible in laboratory searches. For the case of DR, we find a novel complementarity between the measurements of $\Delta N_{\rm eff}$ from these emitted particles and the ISGWB from PBH domination. Our results indicate that the ISGWB has a weak dependence on the initial PBH spin. However, for gravitons as the DR particles, the initial PBH spin plays a significant role, and only above a critical value of the initial spin parameter $a_*$, which depends only on initial PBH mass, the graviton emission can be probed in the CMB-HD experiment. Upcoming CMB experiments such as CMB-HD and CMB-Bharat, together with future GW detectors like LISA and ET, open up an exciting possibility of constraining the PBHs parameter space providing deeper insights into the expansion history of the universe between the end of inflation and BBN.

Keywords: ::

Inflation from Multiple Pseudo-Scalar Fields: PBH Dark Matter and   Gravitational Waves

Published Paper #: 1127

Authors:, Alireza Talebian, Seyed Ali Hosseini Mansoori, Hassan Firouzjahi,

Journal: Astrophys.J. 948 (2023) 1, 48

url: http://arxiv.org/pdf/2210.13822v2.pdf

Abstract: We study a model of inflation with multiple pseudo-scalar fields coupled to a $U(1)$ gauge field through Chern-Simons interactions. Because of parity violating interactions, one polarization of the gauge field is amplified yielding to enhanced curvature perturbation power spectrum. Inflation proceeds in multiple stages as each pseudo-scalar field rolls towards its minimum yielding to distinct multiple peaks in the curvature perturbations power spectrum at various scales during inflation. The localized peaks in power spectrum generate Primordial Black Holes (PBHs) which can furnish a large fraction of Dark Matter (DM) abundance. In addition, gravitational waves (GWs) with non-trivial spectra are generated which are in sensitivity range of various forthcoming GW observatories.

Keywords: ::

Large Deviations in the Early Universe

Published Paper #: 1126

Authors:, Timothy Cohen, Daniel Green, Akhil Premkumar,

Journal: Phys.Rev.D 107 (2023) 8, 083501

url: http://arxiv.org/pdf/2212.02535v2.pdf

Abstract: Fluctuations play a critical role in cosmology. They are relevant across a range of phenomena from the dynamics of inflation to the formation of structure. In many cases, these fluctuations are coarse grained and follow a Gaussian distribution as a consequence of the Central Limit Theorem. Yet, some classes of observables are dominated by rare fluctuations and are sensitive to the details of the underlying microphysics. In this paper, we argue that the Large Deviation Principle can be used to diagnose when one must to appeal to the fundamental description. Concretely, we investigate the regime of validity for the Fokker-Planck equation that governs Stochastic Inflation. For typical fluctuations, this framework leads to the central limit-type behavior expected of a random walk. However, fluctuations in the regime of the Large Deviation Principle are determined by instanton-like saddle points accompanied by a new energy scale. When this energy scale is above the UV cutoff of the EFT, the tail is only calculable in the microscopic description. We explicitly demonstrate this phenomenon in the context of determining the phase transition to eternal inflation, the distribution of scalar field fluctuations in de Sitter, and the production of primordial black holes.

Keywords: ::

Hunting for Dark Matter and New Physics with GECCO

Published Paper #: 1125

Authors:, Adam Coogan, Alexander Moiseev, Logan Morrison, Stefano Profumo, Matthew G. Baring, Aleksey Bolotnikov, Gabriella A. Carini, Sven C. Herrmann, Francesco Longo, Floyd W. Stecker, Alessandro Armando Vigliano, Richard S. Woolf,

Journal: Phys. Rev. D 107, 023022 (2023)

url: http://arxiv.org/pdf/2101.10370v2.pdf

Abstract: We outline the science opportunities in the areas of searches for dark matter and new physics offered by a proposed future MeV gamma-ray telescope, the Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO). We point out that such an instrument would play a critical role in opening up a discovery window for particle dark matter with mass in the MeV or sub-MeV range, in disentangling the origin of the mysterious 511 keV line emission in the Galactic Center region, and in potentially discovering Hawking evaporation from light primordial black holes.

Keywords: ::

Numerical stochastic inflation constrained by frozen noise

Published Paper #: 1124

Authors:, Eemeli Tomberg,

Journal: JCAP04(2023)042

url: http://arxiv.org/pdf/2210.17441v2.pdf

Abstract: Stochastic inflation can resolve strong inflationary perturbations, which seed primordial black holes. I present a fast and accurate way to compute these perturbations in typical black hole producing single-field models, treating the short-wavelength Fourier modes beyond the de Sitter approximation. The squeezing and freezing of the modes reduces the problem to one dimension, and the resulting new form of the stochastic equations, dubbed `constrained stochastic inflation,' can be solved efficiently with semi-analytical techniques and numerical importance sampling. In an example case, the perturbation distribution is resolved in seconds deep into its non-Gaussian tail, a speed-up of factor $10^9$ compared to a previous study. Along the way, I comment on the role of the momentum constraint in stochastic inflation.

Keywords: ::

Generation of primordial black holes from an inflation model with   modified dispersion relation

Published Paper #: 1123

Authors:, Taotao Qiu, Wenyi Wang, Ruifeng Zheng,

Journal: Phys. Rev. D 107, 083018 (2023)

url: http://arxiv.org/pdf/2212.03403v3.pdf

Abstract: A primordial black hole (PBH) is interesting to people for its ability of explaining dark matter as well as supermassive astrophysical objects. In the normal inflation scenario, the generation of PBHs usually requires an enhanced power spectrum of scalar perturbation at the end of inflation era, which is expected when the dispersion relation of the inflaton field gets modified. In this work, we study a kind of inflation model called {the \it Dirac-Born-Infeld-inspired nonminimal kinetic coupling (DINKIC)} model, where the dispersion relation is modified by a square root existing in the field Lagrangian. We discuss the enhancement of scalar power spectrum due to the modified dispersion relation, as well as the abundance of PBHs produced by the Press-Schechter collapse mechanism. We also discuss the formation of scalar-induced gravitational waves by linear scalar perturbations.

Keywords: ::

On the Merger Rate of Primordial Black Holes in Cosmic Voids

Published Paper #: 1122

Authors:, Saeed Fakhry, Seyed Sajad Tabasi, Javad T. Firouzjaee,

Journal: Physics of the Dark Universe (2023)

url: http://arxiv.org/pdf/2210.13558v2.pdf

Abstract: Cosmic voids are known as underdense substructures of the cosmic web that cover a large volume of the Universe. It is known that cosmic voids contain a small number of dark matter halos, so the existence of primordial black holes (PBHs) in these secluded regions of the Universe is not unlikely. In this work, we calculate the merger rate of PBHs in dark matter halos structured in cosmic voids and determine their contribution to gravitational wave events resulting from black hole mergers recorded by the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO)-Advanced Virgo (aVirgo) detectors. Relying on the PBH scenario, the results of our analysis indicate that about $2 \sim 3$ annual events of binary black hole mergers out of all those recorded by the aLIGO-aVirgo detectors should belong to cosmic voids. We also calculate the redshift evolution of the merger rate of PBHs in cosmic voids. The results show that the evolution of the merger rate of PBHs has minimum sensitivity to the redshift changes, which seems reasonable while considering the evolution of cosmic voids. Finally, we specify the behavior of the merger rate of PBHs as a function of their mass and fraction in cosmic voids and we estimate $\mathcal{R} (M_{PBH}, f_{PBH})$ relation, which is well compatible with our findings.

Keywords: ::

Primordial black holes from Volkov-Akulov-Starobinsky supergravity

Published Paper #: 1121

Authors:, Yermek Aldabergenov, Sergei V. Ketov,

Journal: Fortschr. Phys. 2023, 2300039

url: http://arxiv.org/pdf/2301.12750v3.pdf

Abstract: We study the formation of primordial black holes (PBH) in the Starobinsky supergravity coupled to the nilpotent superfield describing Volkov-Akulov goldstino. By using the no-scale K\"ahler potential and a polynomial superpotential, we find that under certain conditions our model can describe effectively single-field inflation with the ultra-slow-roll phase that appears near a critical (nearly-inflection) point of the scalar potential. This can lead to the formation of PBH as part of (or whole) dark matter, while keeping the inflationary spectral tilt and the tensor-to-scalar ratio in good agreement with the current cosmic microwave background (CMB) bounds. After inflation, supersymmetry is spontaneously broken at the inflationary scale with the vanishing cosmological constant.

Keywords: ::

Bayesian Implications for the Primordial Black Holes from NANOGrav's   Pulsar-Timing Data Using the Scalar-Induced Gravitational Waves

Published Paper #: 1120

Authors:, Zhi-Chao Zhao, Sai Wang,

Journal: Universe 2023, 9(4), 157

url: http://arxiv.org/pdf/2211.09450v3.pdf

Abstract: Assuming that the common-spectrum process in the NANOGrav 12.5-year dataset has an origin of scalar-induced gravitational waves, we study the enhancement of primordial curvature perturbations and the mass function of primordial black holes, by performing the Bayesian parameter inference for the first time. We obtain lower limits on the spectral amplitude, i.e., $\mathcal{A}\gtrsim10^{-2}$ at 95\% confidence level, when assuming the power spectrum of primordial curvature perturbations to follow a log-normal distribution function with width $\sigma$. In the case of $\sigma\rightarrow0$, we find that the primordial black holes with $2\times10^{-4}-10^{-2}$ solar mass are allowed to compose at least a fraction $10^{-6}$ of dark matter. Such a mass range is shifted to more massive regimes for larger values of $\sigma$, e.g., to a regime of $4\times10^{-3}-0.2$ solar mass in the case of $\sigma=1$. We expect the planned gravitational-wave experiments to have their best sensitivity to $\mathcal{A}$ in the range of $10^{-4}$ to $10^{-7}$, depending on the experimental setups. With this level of sensitivity, we can search for primordial black holes throughout the entire parameter space, especially in the mass range of $10^{-16}$ to $10^{-11}$ solar masses, where they could account for all dark matter. In addition, the importance of multi-band detector networks is emphasized to accomplish our theoretical expectation.

Keywords: ::

Boosted dark matter from primordial black holes produced in a   first-order phase transition

Published Paper #: 1119

Authors:, Danny Marfatia, Po-Yan Tseng,

Journal: JHEP 2304:006 (2023)

url: http://arxiv.org/pdf/2212.13035v2.pdf

Abstract: During a cosmological first-order phase transition in a dark sector, fermion dark matter particles $\chi$ can form macroscopic Fermi balls that collapse to primordial black holes (PBHs) under certain conditions. The evaporation of the PBHs produces a boosted $\chi$ flux, which may be detectable if $\chi$ couples to visible matter. We consider the interaction of $\chi$ with electrons, and calculate signals of the dark matter flux in the XENON1T, XENONnT, Super-Kamiokande and Hyper-Kamiokande experiments. A correlated gravitational wave signal from the phase transition can be observed at THEIA and $\mu$Ares. An amount of dark radiation measurable by CMB-S4 is an epiphenomenon of the phase transition.

Keywords: ::

Primordial black holes and scalar-induced gravitational waves from the   generalized Brans-Dicke theory

Published Paper #: 1118

Authors:, Zhu Yi,

Journal: JCAP03(2023)048

url: http://arxiv.org/pdf/2206.01039v2.pdf

Abstract: The power spectrum of the scalar-tensor inflation with a quadratic form Ricci scalar coupling function $\Omega(\phi)=1- 2\phi/\phi_c+(1+\delta^2)(\phi/\phi_c)^2$ can be enhanced enough to produce primordial black holes and generate scalar-induced gravitational waves. The masses of primordial black holes and the frequencies of scalar-induced gravitational waves are controlled by the parameter $\phi_c$, and their amplitudes are determined by the parameter $\delta$. Primordial black holes with stellar masses, planetary masses, and masses around $10^{-12} M_\odot$ are produced and their abundances are obtained from the peak theory. The frequencies of the corresponding scalar-induced gravitational waves are around $10^{-9}$ Hz, $10^{-6}$ Hz, and $10^{-3}$ Hz, respectively. The primordial black holes with masses around $10^{-12} M_\odot$ can account for almost all of the dark matter, and the scalar-induced gravitational waves with frequencies around $10^{-9}$ Hz can explain the NANOGrav 12.5yrs signal.

Keywords: ::

PBH-infused seesaw origin of matter and unique gravitational waves

Published Paper #: 1117

Authors:, Debasish Borah, Suruj Jyoti Das, Rome Samanta, Federico R. Urban,

Journal: JHEP03(2023)127

url: http://arxiv.org/pdf/2211.15726v2.pdf

Abstract: The Standard Model, extended with three right-handed (RH) neutrinos, is the simplest model that can explain light neutrino masses, the baryon asymmetry of the Universe, and dark matter (DM). Models in which RH neutrinos are light are generally easier to test in experiments. In this work, we show that, even if the RH neutrinos are super-heavy ($M_{i=1,2,3}>10^9$ GeV) -- close to the Grand Unification scale -- the model can be tested thanks to its distinct features on the stochastic Gravitational Wave (GW) background. We consider an early Universe filled with ultralight primordial black holes (PBH) that produce a super-heavy RH neutrino DM via Hawking radiation. The other pair of RH neutrinos generates the baryon asymmetry via thermal leptogenesis, much before the PBHs evaporate. GW interferometers can test this novel spectrum of masses thanks to the GWs induced by the PBH density fluctuations. In a more refined version, wherein a $U(1)$ gauge symmetry breaking dynamically generates the seesaw scale, the PBHs also cause observable spectral distortions on the GWs from the $U(1)$-breaking cosmic strings. Thence, a low-frequency GW feature related to DM genesis and detectable with a pulsar-timing array must correspond to a mid- or high-frequency GW signature related to baryogenesis at interferometer scales.

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Reconstruction of Power Spectrum of Primordial Curvature Perturbations   on small scales from Primordial Black Hole Binaries scenario of LIGO/VIRGO   detection

Published Paper #: 1116

Authors:, Xinpeng Wang, Ying-li Zhang, Rampei Kimura, Masahide Yamaguchi,

Journal: Sci.China Phys.Mech.Astron. 66 (2023) 6, 260462

url: http://arxiv.org/pdf/2209.12911v3.pdf

Abstract: As a candidate bound for the Binary Black Hole (BBH) merger events detected by LIGO/Virgo, Primordial Black Holes (PBHs) provide a useful tool to investigate the primordial curvature perturbations on small scales. Using the GWTC-1 to GWTC-3 catalogs, under the scenario that PBHs originate from large primordial curvature perturbations on small scales during inflationary epoch, we for the first time reconstruct the power spectrum of primordial curvature perturbations on small scales. It is found that the value of the amplitude of the primordial power spectrum is enhanced to $\mathcal{O}(10^{-2})$ on scales $\mathcal{O}(1)$ pc. This may imply the validity of PBH as a possible BBH merger candidate.

Keywords: ::

Conformally Schwarzschild cosmological black holes

Published Paper #: 1115

Authors:, Takuma Sato, Hideki Maeda, Tomohiro Harada,

Journal: Class. Quant. Grav. 39 (2022) 21, 215011

url: http://arxiv.org/pdf/2206.10998v3.pdf

Abstract: We thoroughly investigate conformally Schwarzschild spacetimes in different coordinate systems to seek for physically reasonable models of a cosmological black hole. We assume that a conformal factor depends only on the time coordinate and that the spacetime is asymptotically flat Friedmann-Lema\^{\i}tre-Robertson-Walker universe filled by a perfect fluid obeying a linear equation state $p=w\rho$ with $w>-1/3$. In this class of spacetimes, the McClure-Dyer spacetime, constructed in terms of the isotropic coordinates, and the Thakurta spacetime, constructed in terms of the standard Schwarzschild coordinates, are identical and do not describe a cosmological black hole. In contrast, the Sultana-Dyer and Culetu classes of spacetimes, constructed in terms of the Kerr-Schild and Painlev\'{e}-Gullstrand coordinates, respectively, describe a cosmological black hole. In the Sultana-Dyer case, the corresponding matter field in general relativity can be interpreted as a combination of a homogeneous perfect fluid and an inhomogeneous null fluid, which is valid everywhere in the spacetime unlike Sultana and Dyer's interpretation. In the Culetu case, the matter field can be interpreted as a combination of a homogeneous perfect fluid and an inhomogeneous anisotropic fluid. However, in both cases, the total energy-momentum tensor violates all the standard energy conditions at a finite value of the radial coordinate in late times. As a consequence, the Sultana-Dyer and Culetu black holes for $-1/3<w\le 1$ cannot describe the evolution of a primordial black hole after its horizon entry.

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Gravitational-wave Emission from a Primordial Black Hole Inspiraling   inside a Compact Star: a Novel Probe for Dense Matter Equation of State

Published Paper #: 1114

Authors:, Ze-Cheng Zou, Yong-Feng Huang,

Journal: The Astrophysical Journal Letters (ApJL), 928:L13, 2022

url: http://arxiv.org/pdf/2201.00369v4.pdf

Abstract: Primordial black holes of planetary masses captured by compact stars are widely studied to constrain their composition fraction of dark matter. Such a capture may lead to an inspiral process and be detected through gravitational wave signals. In this Letter, we study the post-capture inspiral process by considering two different kinds of compact stars, i.e., strange stars and neutron stars. The dynamical equations are numerically solved and the gravitational wave emission is calculated. It is found that the Advanced LIGO can detect the inspiraling of a $10^{-5}$ solar mass primordial black hole at a distance of 10 kpc, while a Jovian-mass case can even be detected at megaparsecs. Promisingly, the next generation gravitational wave detectors can detect the cases of $10^{-5}$ solar mass primordial black holes up to ${\sim}1$ Mpc, and can detect Jovian-mass cases at several hundred megaparsecs. Moreover, the kilohertz gravitational wave signal shows significant differences for strange stars and neutron stars, potentially making it a novel probe to the dense matter equation of state.

Keywords: ::

Primordial black holes from Higgs inflation with a Gauss-Bonnet coupling

Published Paper #: 1113

Authors:, Ryodai Kawaguchi, Shinji Tsujikawa,

Journal: Phys. Rev. D 107, 063508 (2023)

url: http://arxiv.org/pdf/2211.13364v2.pdf

Abstract: Primordial black holes (PBHs) can be the source for all or a part of today's dark matter density. Inflation provides a mechanism for generating the seeds of PBHs in the presence of a temporal period where the velocity of an inflaton field $\phi$ rapidly decreases toward 0. We compute the primordial power spectra of curvature perturbations generated during Gauss-Bonnet (GB) corrected Higgs inflation in which the inflaton field has not only a nonminimal coupling to gravity but also a GB coupling. For a scalar-GB coupling exhibiting a rapid change during inflation, we show that curvature perturbations are sufficiently enhanced by the appearance of an effective potential $V_{\rm eff}(\phi)$ containing the structures of plateau-type, bump-type, and their intermediate type. We find that there are parameter spaces in which PBHs can constitute all dark matter for these three types of $V_{\rm eff}(\phi)$. In particular, models with bump- and intermediate-types give rise to the primordial scalar and tensor power spectra consistent with the recent Planck data on scales relevant to the observations of cosmic microwave background. This property is attributed to the fact that the number of e-foldings $\Delta N_c$ acquired around the bump region of $V_{\rm eff}(\phi)$ can be as small as a few, in contrast to the plateau-type where $\Delta N_c$ typically exceeds the order of 10.

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Aspects of Quantum Gravity Phenomenology and Astrophysics

Published Paper #: 1112

Authors:, Arundhati Dasgupta, José Fajardo-Montenegro,

Journal: Universe 9(3) 128 (2023)

url: http://arxiv.org/pdf/2303.05042v1.pdf

Abstract: With the discovery of gravitational waves, the search for the quantum of gravity, the graviton, is imminent. We discuss the current status of the bounds on graviton mass from experiments as well as the theoretical understanding of these particles. We provide an overview of current experiments in astrophysics such as the search for Hawking radiation in gamma-ray observations and neutrino detectors, which will also shed light on the existence of primordial black holes. Finally, the semiclassical corrections to the image of the event horizon are discussed.

Keywords: ::

Primordial Gravitational Wave Circuit Complexity

Published Paper #: 1111

Authors:, Kiran Adhikari, Sayantan Choudhury, Hardey N. Pandya, Rohan Srivastava,

Journal: Symmetry 2023, 15(3), 664

url: http://arxiv.org/pdf/2108.10334v3.pdf

Abstract: In this article, we investigate various physical implications of quantum circuit complexity using squeezed state formalism of Primordial Gravitational Waves (PGW). Recently quantum information theoretic concepts, such as entanglement entropy, and complexity are playing a pivotal role to understand the dynamics of quantum system even in the diverse fields such as, high energy physics and cosmology. This paper is devoted in studying quantum circuit complexity of PGW for various cosmological models, such as de Sitter, inflation, radiation, reheating, matter, bouncing, cyclic and black hole gas model etc. We compute complexity measure using both Covariance and Nielsen's wave function method for three different choices of quantum initial vacua: Motta-Allen, $\alpha$ and Bunch-Davies. Besides computing circuit complexity, we have also computed Von-Neumann entanglement entropy. By making the comparison of complexity with entanglement entropy, we are able to probe various features regarding the dynamics of evolution for different cosmological models. Because entanglement entropy is independent of the squeezing angle, we are able to understand more details of the system using Nielsen's measure of complexity which is dependent on both squeezing parameter and angle. This implies that quantum complexity could indeed be a useful probe to study quantum features in cosmological scale. Quantum complexity is also becoming a powerful technique to understand the chaotic behaviour and random fluctuations of quantum fields. Using the growth of complexity, we are able to compute quantum Lyapunov exponent for various cosmological models and comment on it's chaotic nature.

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Isotropic X-ray bound on Primordial Black Hole Dark Matter

Published Paper #: 1110

Authors:, J. Iguaz, P. D. Serpico, T. Siegert,

Journal: Phys. Rev. D 103, 103025 (2021)

url: http://arxiv.org/pdf/2104.03145v2.pdf

Abstract: We revisit the constraints on evaporating primordial black holes (PBHs) from the isotropic X-ray and soft gamma-ray background in the mass range $10^{16}-10^{18}$ g. We find that they are stronger than usually inferred due to two neglected effects: i) The contribution of the annihilation radiation due to positrons emitted in the evaporation process. ii) The high-latitude, Galactic contribution to the measured isotropic flux. We study the dependence of the bounds from the datasets used, the positron annihilation conditions, and the inclusion of the astrophysical background. We push the exclusion limit for non-spinning PBH with monochromatic mass function as the totality of dark matter to 1.5$\times 10^{17}\,$g, which represents a $\sim$15$\%$ improvement with respect to earlier bounds and translates into almost an order of magnitude improvement in the PBH fraction in the already probed region. We also show that the inclusion of spin and/or an extended, log-normal mass function lead to tighter bounds. Our study suggests that the isotropic flux is an extremely promising target for future missions in improving the sensitivity to PBHs as candidates for dark matter.

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Effect of a High-Precision Semi-Analytical Mass Function on the Merger   Rate of Primordial Black Holes in Dark Matter Halos

Published Paper #: 1109

Authors:, Saeed Fakhry, Antonino Del Popolo,

Journal: Phys. Rev. D (2023)

url: http://arxiv.org/pdf/2212.08646v2.pdf

Abstract: In this work, we study the effect of a high-precision semianalytical mass function on the merger rate of primordial black holes (PBHs) in dark matter halos. For this purpose, we first explain a theoretical framework for dark matter halo models and introduce relevant quantities such as halo density profile, concentration parameter, and a high-precision semianalytical function namely Del Popolo (DP) mass function. In the following, we calculate the merger rate of PBHs in the framework of ellipsoidal-collapse dark matter halo models while considering the DP mass function, and compare it with our previous study for the Sheth-Tormen (ST) mass function. The results show that by taking the mass of PBHs as $M_{\rm PBH} = 30M_{\odot}$, the DP mass function can potentially amplify the merger rate of PBHs. Moreover, we calculate the merger rate of PBHs for the DP mass function as a function of their mass and fraction and compare it with the black hole mergers recorded by the LIGO-Virgo detectors during the latest observing run. Our findings show that the merger rate of PBHs will fall within the LIGO-Virgo band if $f_{\rm PBH} \gtrsim \mathcal{O}(10^{-1})$. This implies that the DP mass function can be used to strengthen constraints on the fraction of PBHs.

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Catastrogenesis: DM, GWs, and PBHs from ALP string-wall networks

Published Paper #: 1108

Authors:, Graciela B. Gelmini, Anna Simpson, Edoardo Vitagliano,

Journal: JCAP 02 (2023) 031 JCAP 02 (2023) 031 JCAP 02 (2023) 031 JCAP 02
 (2023) 031 JCAP 02 (2023) 031 JCAP 02 (2023) 031

url: http://arxiv.org/pdf/2207.07126v2.pdf

Abstract: Axion-like particles (ALPs), a compelling candidate for dark matter (DM), are the pseudo Nambu-Goldstone bosons of a spontaneously and explicitly broken global $U(1)$ symmetry. When the symmetry breaking happens after inflation, the ALP cosmology predicts the formation of a string-wall network which must annihilate early enough, producing gravitational waves (GWs) and primordial black holes (PBHs), as well as non-relativistic ALPs. We call this process catastrogenesis. We show that, under the generic assumption that the potential has several degenerate minima, GWs from string-wall annihilation at temperatures below 100 eV could be detected by future CMB and astrometry probes, for ALPs with mass from $10^{-16}$ to $10^{6}\,\rm eV$. In this case, structure formation could limit ALPs to constitute a fraction of the DM and the annihilation would produce mostly ``stupendously large" PBHs. For larger annihilation temperatures, ALPs can constitute $100\%$ of DM, and the annihilation could produce supermassive black holes with a mass of up to $10^9\, M_\odot$ as found at the center of large galaxies. Therefore our model could solve two mysteries, the nature of the DM and the origin of these black holes.

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Gravitational microlensing by dressed primordial black holes

Published Paper #: 1107

Authors:, Rong-Gen Cai, Tan Chen, Shao-Jiang Wang, Xing-Yu Yang,

Journal: JCAP03(2023)043

url: http://arxiv.org/pdf/2210.02078v2.pdf

Abstract: The accretion of dark matter around the primordial black holes (PBHs) could lead to the formation of surrounding minihalos, whose mass can be several orders of magnitude higher than the central PBH mass. The gravitational microlensing produced by such dressed PBHs could be quite different from that of the bare PBHs, which may significantly affect the constraints on the PBH abundance. In this paper, we study the gravitational microlensing produced by dressed PBHs in detail. We find that all the microlensing effects by dressed PBHs have asymptotic behavior depending on the minihalo size, which can be used to predict the microlensing effects by comparing the halo size with the Einstein radius. When the minihalo radius and the Einstein radius are comparable, the effect of the density distribution of the halo is significant to the microlensing. Applying the stellar microlensing by dressed PBHs to the data of the Optical Gravitational Lensing Experiment and Subaru/HSC Andromeda observations, we obtain the improved constraints on the PBH abundance. It shows that the existence of dark matter minihalos surrounding PBHs can strengthen the constraints on the PBH abundance from stellar microlensing by several orders, and can shift the constraints to the well-known asteroid mass window where PBHs can constitute all the dark matter.

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Bounds from multi-messenger astronomy on the Super Heavy Dark Matter

Published Paper #: 1106

Authors:, M. Deliyergiyev, A. Del Popolo, Morgan Le Delliou,

Journal: Phys.Rev.D 106 (2022) 6, 063002

url: http://arxiv.org/pdf/2209.14061v2.pdf

Abstract: The purely gravitational evidence supporting the need for dark matter (DM) particles is compelling and based on Galactic to cosmological scale observations. Thus far, the promising weakly interacting massive particles scenarios have eluded detection, motivating alternative models for DM. We consider the scenarios involving the superheavy dark matter (SHDM) that potentially can be emitted by primordial black holes (PBHs) and can decay or annihilate into ultrahigh-energy (UHE) neutrinos and photons. The observation of a population of photons with energies $E\ge 10^{11}$ GeV would imply the existence of completely new physical phenomena, or shed some light on DM models. Only the ultra-high energy cosmic ray observatories have the capabilities to detect such UHE decay products via the measurements of UHE photon induced extensive air showers. Using the upper bound on the flux of UHE cosmic rays beyond $10^{11.3}$ GeV implying $J(>10^{11.3}~{\rm{GeV}})< 3.6\times 10^{-5}$ km$^{-2}$sr$^{-1}$y$^{-1}$, at the $90\%$ C.L. reported by the Pierre Auger Observatory, we obtain global limits on the lifetime of the DM particles with masses $10^{15}\le M_{X} \le 10^{17}$ GeV. The constraints derived here are new and cover a region of the parameter space not yet explored. We compare our results with the projected constraints from future POEMMA and JEM-EUSO experiments, in order to quantify the improvement that will be obtained by these missions.   Moreover, assuming that an epoch of early PBHs domination introduces a unique spectral break, $f_{\ast}$, in the gravitational wave spectrum, the frequency of which is related to the SHDM mass, we map potential probes and limits of the DM particles masses on the $f_{\ast}-M_{X}$ parameter space.

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Constraining the Barbero-Immirzi parameter from the duration of   inflation in loop quantum cosmology

Published Paper #: 1105

Authors:, L. N. Barboza, G. L. L. W. Levy, L. L. Graef, Rudnei O. Ramos,

Journal: Phys. Rev. D 106, 103535 (2022)

url: http://arxiv.org/pdf/2206.14881v3.pdf

Abstract: We revisit the predictions for the duration of the inflationary phase after the bounce in loop quantum cosmology. We present our analysis for different classes of inflationary potentials that include the monomial power-law chaotic type of potentials, the Starobinsky and the Higgs-like symmetry breaking potential with different values for the vacuum expectation value. Our setup can easily be extended to other forms of primordial potentials than the ones we have considered. Independently on the details of the contracting phase, if the dynamics starts sufficiently in the far past, the kinetic energy will come to dominate at the bounce, uniquely determining the amplitude of the inflaton at this moment. This will be the initial condition for the further evolution that will provide us with results for the number of e-folds from the bounce to the beginning of the accelerated inflationary regime and the subsequent duration of inflation. We also discuss under which conditions each model considered could lead to observable signatures on the spectrum of the cosmic microwave background or else be excluded for not predicting a sufficient amount of accelerated expansion. A first analysis is performed considering the standard value for the Barbero-Immirzi parameter obtained from black hole entropy calculations. In a second analysis, we consider the possibility of varying the value of this parameter, which is motivated by the fact that the Barbero-Immirzi parameter can be considered a free parameter of the underlying quantum theory in the context of loop quantum gravity. From this analysis, we obtain a lower limit for this parameter by requiring the minimum amount of inflationary expansion that makes the model consistent with the CMB observations. [abridged]

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Primordial Black Hole Formation in Non-Standard Post-Inflationary Epochs

Published Paper #: 1104

Authors:, Sukannya Bhattacharya,

Journal: Galaxies 2023, 11(1), 35

url: http://arxiv.org/pdf/2302.12690v1.pdf

Abstract: When large overdensities gravitationally collapse in the early universe, they lead to primordial black holes (PBH). Depending on the exact model of inflation leading to necessary large perturbations at scales much smaller than scales probed at the Cosmic Microwave Background (CMB) surveys, PBHs of masses $\lesssim$$10^3 M_{\odot}$ can be formed sometime between the end of inflation and nucleosynthesis. However, the lack of a direct probe for the exact expansion history of the universe in this duration introduces uncertainties in the PBH formation process. The presence of alternate cosmological evolution for some duration after inflation affects the relation between (i) PBH mass and the scale of the collapsing overdensity; and (ii) PBH abundance and amplitude of the overdensities. In this review, the non-standard cosmological epochs relevant for a difference in PBH production are motivated and discussed. The importance of developing the framework of PBH formation in non-standard epochs is discussed from a phenomenological point of view, with particular emphasis on the advances in gravitational wave (GW) phenomenology, since abundant PBHs are always accompanied by large induced GWs. PBH formation in general non-standard epochs is also reviewed including the mathematical formalism. Specific examples, such as PBH formation in a kinetic energy dominated epoch and an early matter dominated epoch, are discussed with figures showing higher PBH abundances as compared to the production in standard radiation domination.

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Impact of LIGO-Virgo black hole binaries on gravitational wave   background searches

Published Paper #: 1103

Authors:, Marek Lewicki, Ville Vaskonen,

Journal: Eur. Phys. J. C 83, 168 (2023)

url: http://arxiv.org/pdf/2111.05847v2.pdf

Abstract: We study the impact of the black hole binary population currently probed by LIGO-Virgo on future searches for the primordial gravitational wave background. We estimate the foreground generated by the binaries using the observed event rate and a simple modeling of the black hole population. We subtract individually resolvable binaries from the foreground and utilize Fisher analysis to derive sensitivity curves for power-law signals including these astrophysical foregrounds. Even with optimistic assumptions, we find that the reach of future experiments will be severely reduced.

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Fitting power spectrum of scalar perturbations for primordial black hole   production during inflation

Published Paper #: 1102

Authors:, Daniel Frolovsky, Sergei V. Ketov,

Journal: Astronomy 2023, 2, 47-57

url: http://arxiv.org/pdf/2302.06153v2.pdf

Abstract: We propose a simple analytic fit for the power spectrum of scalar (curvature) perturbations during inflation, in order to describe slow roll of inflaton and formation of primordial black holes in the early universe, in the framework of single-field models. Our fit is given by a sum of the power spectrum in the slow-roll approximation, needed for a viable description of the cosmic microwave background radiation in agreement with Planck/BICEP/Keck measurements, and the log-normal (Gaussian) fit for the power spectrum enhancement (peak) needed for efficient production of primordial black holes. We use the T-type $\alpha$-attractor models in order to describe slow-roll inflation. Demanding the location and height of the peak to yield the masses of primordial black holes in the asteroid-size window allowed for the whole (current) dark matter to be composed of the primordial black holes, we find the restrictions on the remaining parameters and, most notably, on the width of the peak.

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Primordial black holes from stochastic tunnelling

Published Paper #: 1101

Authors:, Chiara Animali, Vincent Vennin,

Journal: JCAP 02(2023) 043

url: http://arxiv.org/pdf/2210.03812v2.pdf

Abstract: If the inflaton gets trapped in a local minimum of its potential shortly before the end of inflation, it escapes by building up quantum fluctuations in a process known as stochastic tunnelling. In this work we study cosmological fluctuations produced in such a scenario, and how likely they are to form Primordial Black Holes (PBHs). This is done by using the stochastic-$\delta N$ formalism, which allows us to reconstruct the highly non-Gaussian tails of the distribution function of the number of $e$-folds spent in the false-vacuum state. We explore two different toy models, both analytically and numerically, in order to identify which properties do or do not depend on the details of the false-vacuum profile. We find that when the potential barrier is small enough compared to its width, $\Delta V/V < \Delta\phi^2/M_{\text{Pl}}^2$, the potential can be approximated as being flat between its two local extrema, so results previously obtained in a "flat quantum well'' apply. Otherwise, when $\Delta V/V < V/M_{\text{Pl}}^4$, the PBH abundance depends exponentially on the height of the potential barrier, and when $\Delta V/V > V/M_{\text{Pl}}^4$ it depends super-exponentially ( i.e. as the exponential of an exponential) on the barrier height. In that later case PBHs are massively produced. This allows us to quantify how much flat inflection points need to be fine-tuned. In a deep false vacuum, we also find that slow-roll violations are typically encountered unless the potential is close to linear. This motivates further investigations to generalise our approach to non-slow-roll setups.

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Primordial Gravitational Waves From Black Hole Evaporation in Standard   and Non-Standard Cosmologies

Published Paper #: 1100

Authors:, Aurora Ireland, Stefano Profumo, Jordan Scharnhorst,

Journal: Physical Review D, Vol. 107, No. 10 (2023)

url: http://arxiv.org/pdf/2302.10188v1.pdf

Abstract: Gravitons radiated from light, evaporating black holes contribute to the stochastic background of gravitational waves. The spectrum of such emission depends on both the mass and the spin of the black holes, as well as on the redshifting that occurs between the black hole formation and today. This, in turn, depends on the expansion history of the universe, which is largely unknown and unconstrained at times prior to the synthesis of light elements. Here, we explore the features of the stochastic background of gravitational waves from black hole evaporation under a broad range of possible early cosmological histories. The resulting gravitational wave signals typically peak at very high frequencies, and offer opportunities for proposed ultra-high frequency gravitational wave detectors. Lower-frequency peaks are also possible, albeit with a suppressed intensity that is likely well below the threshold of detectability. We find that the largest intensity peaks correspond to cosmologies dominated by fluids with equations of state that have large pressure-to-density ratios. Such scenarios can be constrained on the basis of violation of $\Delta N_{\rm eff}$ bounds.

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Primordial non-gaussianity up to all orders: theoretical aspects and   implications for primordial black hole models

Published Paper #: 1099

Authors:, Giacomo Ferrante, Gabriele Franciolini, Antonio Junior Iovino, Alfredo Urbano,

Journal: Phys. Rev. D 107, 043520 (16/02/2022)

url: http://arxiv.org/pdf/2211.01728v2.pdf

Abstract: We develop an exact formalism for the computation of the abundance of primordial black holes (PBHs) in the presence of local non-gaussianity (NG) in the curvature perturbation field. For the first time, we include NG going beyond the widely used quadratic and cubic approximations, and consider a completely generic functional form. Adopting threshold statistics of the compaction function, we address the computation of the abundance both for narrow and broad power spectra. While our formulas are generic, we discuss explicit examples of phenomenological relevance considering the physics case of the curvaton field. We carefully assess under which conditions the conventional perturbative approach can be trusted. In the case of a narrow power spectrum, this happens only if the perturbative expansion is pushed beyond the quadratic order (with the optimal order of truncation that depends on the width of the spectrum). Most importantly, we demonstrate that the perturbative approach is intrinsically flawed when considering broad spectra, in which case only the non-perturbative computation captures the correct result. Finally, we describe the phenomenological relevance of our results for the connection between the abundance of PBHs and the stochastic gravitational wave (GW) background related to their formation. As NGs modify the amplitude of perturbations necessary to produce a given PBHs abundance and boost PBHs production at large scales for broad spectra, modelling these effects is crucial to connect the PBH scenario to its signatures at current and future GWs experiments.

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Threshold of Primordial Black Hole Formation in Nonspherical Collapse

Published Paper #: 1098

Authors:, Chul-Moon Yoo, Tomohiro Harada, Hirotada Okawa,

Journal: Phys. Rev. D 102, 043526 (2020), Phys. Rev. D 107, 049901
 (erratum)

url: http://arxiv.org/pdf/2004.01042v3.pdf

Abstract: We perform (3+1)-dimensional simulations of primordial black hole (PBH) formation starting from the spheroidal super-horizon perturbations. We investigate how the ellipticity (prolateness or oblateness) affects the threshold of PBH formation in terms of the peak amplitude of curvature perturbation. We find that, in the case of the radiation-dominated universe, the effect of ellipticity on the threshold is negligibly small for the large amplitude of perturbations expected for PBH formation.

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Primordial black holes and scalar-induced gravitational waves from the   perturbations on the inflaton potential in peak theory

Published Paper #: 1097

Authors:, Ji-Xiang Zhao, Xiao-Hui Liu, Nan Li,

Journal: Physical Review D 107, 043515 (2023)

url: http://arxiv.org/pdf/2302.06886v1.pdf

Abstract: A perturbation on the background inflaton potential can lead inflation into the ultraslow-roll stage and can thus remarkably enhance the power spectrum ${\cal P}_{\cal R}(k)$ of the primordial curvature perturbation on small scales. Such an enhanced ${\cal P}_{\cal R}(k)$ will result in primordial black holes (PBHs), contributing a significant fraction of dark matter, and will simultaneously generate sizable scalar-induced gravitational waves (SIGWs) as a secondorder effect. In this work, we calculate the PBH abundances $f_{\rm PBH}(M)$ and SIGW spectra $\Omega_{\rm GW}(f)$ in peak theory. We obtain the PBHs with desirable abundances in one or two typical mass windows at $10^{-17}\, M_\odot$, $10^{-13}\, M_\odot$, and $30\, M_\odot$, respectively. At the same time, the relevant SIGWs are expected to be observed by the next-generation gravitational wave detectors, without spoiling the current constraint. Especially, the SIGW associated with the PBH of $30\, M_\odot$ can also interpret the potential isotropic stochastic gravitational wave background from the NANOGrav 12.5-year dataset.

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A Study of Primordial Very Massive Star Evolution

Published Paper #: 1096

Authors:, Guglielmo Volpato, Paola Marigo, Guglielmo Costa, Alessandro Bressan, Michele Trabucchi, Léo Girardi,

Journal: The Astrophysical Journal, 2023, Volume 944, Number 1, 14 pages

url: http://arxiv.org/pdf/2212.09629v3.pdf

Abstract: We present new evolutionary models of primordial very massive stars, with initial masses ranging from $100\,\mathrm{{M}_{\odot}}$ to $1000\,\mathrm{{M}_{\odot}}$, that extend from the main sequence until the onset of dynamical instability caused by the creation of electron-positron pairs during core C, Ne, or O burning, depending on the star's mass and metallicity. Mass loss accounts for radiation-driven winds as well as pulsation-driven mass-loss on the main sequence and during the red supergiant phase. After examining the evolutionary properties, we focus on the final outcome of the models and associated compact remnants. Stars that avoid the pair-instability supernova channel, should produce black holes with masses ranging from $\approx 40\, \mathrm{{M}_{\odot}}$ to $\approx 1000\,\mathrm{{M}_{\odot}}$. In particular, stars with initial masses of about $100\,\mathrm{{M}_{\odot}}$ could leave black holes of $\simeq 85-90\, \mathrm{{M}_{\odot}}$, values consistent with the estimated primary black hole mass of the GW190521 merger event. Overall, these results may contribute to explain future data from next-generation gravitational-wave detectors, such as the Einstein Telescope and Cosmic Explorer, which will have access to as-yet unexplored BH mass range of $\approx 10^2-10^4\,\mathrm{{M}_{\odot}}$ in the early universe.

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Gravitational waves from the merger of two primordial black hole   clusters

Published Paper #: 1095

Authors:, Yury Eroshenko, Viktor Stasenko,

Journal: Symmetry 15, 637 (2023)

url: http://arxiv.org/pdf/2302.05167v1.pdf

Abstract: The orbital evolution of a binary system consisting of two primordial black hole clusters is investigated. Such clusters are predicted in some theoretical models with broken symmetry in the inflation Lagrangian. A cluster consists of the most massive central black hole surrounded by many smaller black holes. Similar to single primordial black holes, clusters can form gravitationally bounded pairs and merge during their orbital evolution. The replacement of single black holes by such clusters significantly changes the entire merger process and the final rate of gravitational wave bursts in some parameter ranges (with sufficiently large cluster radii). A new important factor is the tidal gravitational interaction of the clusters. It leads to an additional dissipation of the orbital energy, which is transferred into the internal energy of the clusters or carried away by black holes flying out of the clusters. Comparison with the data of gravitational-wave telescopes allows one to constrain the fractions of primordial black holes in clusters, depending on their mass and compactness. Even the primordial black hole fraction in the composition of dark matter $\simeq1$ turns out to be compatible with LIGO/Virgo observational data, if the black holes are in clusters.

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Primordial Black Hole Formation during a Strongly Coupled Crossover

Published Paper #: 1094

Authors:, Albert Escrivà, Javier G. Subils,

Journal: Phys. Rev. D 107, L041301 (2023)

url: http://arxiv.org/pdf/2211.15674v3.pdf

Abstract: The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyze the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\rm{PBH}}\in[10^{-16},10^{-6}]M_{\odot}$.

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Observational imprints of enhanced scalar power on small scales in ultra   slow roll inflation and associated non-Gaussianities

Published Paper #: 1093

Authors:, H. V. Ragavendra, L. Sriramkumar,

Journal: Galaxies 11, 34 (2023)

url: http://arxiv.org/pdf/2301.08887v2.pdf

Abstract: The discovery of gravitational waves from merging binary black holes has generated considerable interest in examining whether these black holes could have a primordial origin. If a significant number of black holes have to be produced in the early universe, the primordial scalar power spectrum should have an enhanced amplitude on small scales, when compared to the COBE normalized values on the larger scales that is strongly constrained by the anisotropies in the cosmic microwave background. In the inflationary scenario driven by a single, canonical scalar field, such power spectra can be achieved in models that permit a brief period of ultra slow roll inflation during which the first slow roll parameter decreases exponentially. In this review, we shall consider a handful of such inflationary models as well as a reconstructed scenario and examine the extent of formation of primordial black holes and the generation of secondary gravitational waves in these cases. We shall also discuss the strength and shape of the scalar bispectrum and the associated non-Gaussianity parameter that arise in such situations. We shall conclude with an outlook wherein we discuss the wider implications of the increased strengths of the non-Gaussianities on smaller scales.

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Dark matter from primordial black holes would hold charge

Published Paper #: 1092

Authors:, Ignacio J. Araya, Nelson D. Padilla, Marcelo E. Rubio, Joaquín Sureda, Juan Magaña, Loreto Osorio,

Journal: JCAP02(2023)030

url: http://arxiv.org/pdf/2207.05829v3.pdf

Abstract: We explore the possibility that primordial black holes (PBHs) contain electric charge down to the present day. We find that PBHs should hold a non-zero net charge at their formation, due to either Poisson fluctuations at horizon crossing or high-energy particle collisions. Although initial charge configurations are subject to fast discharge processes through particle accretion or quantum particle emission, we show that maximally rotating PBHs could produce magnetic fields able to shield them from discharge. Moreover, given that electrons are the lightest and fastest charge carriers, we show that the plasma within virialised dark matter haloes can endow PBHs with net negative charge. We report charge-to-mass ratios between $10^{-31}\,C/\mbox{kg}$ and $10^{-15}\,C/\mbox{kg}$ for PBHs within the mass windows that allow them to constitute the entirety of the dark matter in the Universe.

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Non-linear Electrodynamics in Blandford-Znajeck Energy Extraction

Published Paper #: 1091

Authors:, Amodio Carleo, Gaetano Lambiase, Ali Övgün,

Journal: ANNALEN DER PHYSIK 2023, 2200635

url: http://arxiv.org/pdf/2210.11162v2.pdf

Abstract: Non-linear electrodynamics (NLED) is a generalization of Maxwell's electrodynamics for strong fields. It could have significant implications for the study of black holes and cosmology and have been extensively studied in the literature, extending from quantum to cosmological contexts. Recently, its application to black holes, inflation and dark energy has caught on, being able to provide an accelerated Universe and address some current theoretical inconsistencies, such as the Big Bang singularity. In this work, we report two new ways to investigate these non-linear theories. First, we have analyzed the Blandford-Znajeck mechanism in light of this promising theoretical context, providing the general form of the extracted power up to second order in the black hole spin parameter $a$. We have found that, depending on the NLED model, the emitted power can be extremely increased or decreased, and that the magnetic field lines around the black hole seems to become vertical quickly. Considering only separated solutions, we have found that no monopole solutions exist and this could have interesting astrophysical consequences (not considered here). Last but not least, we attempted to confine the NLED parameters by inducing the amplification of primordial magnetic fields ('seeds'), thus admitting non-linear theories already during the early stages of the Universe. However, the latter approach proved to be useful for NLED research only in certain models. Our (analytical) results emphasize that the existence and behavior of non-linear electromagnetic phenomena strongly depend on the physical context and that only a power-low model seems to have any chance to compete with Maxwell.

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Wash-in leptogenesis after axion inflation

Published Paper #: 1090

Authors:, Valerie Domcke, Kohei Kamada, Kyohei Mukaida, Kai Schmitz, Masaki Yamada,

Journal: JHEP 01 (2023) 053

url: http://arxiv.org/pdf/2210.06412v2.pdf

Abstract: CP violation and the violation of baryon-minus-lepton number B-L do not necessarily have to occur simultaneously in order to accomplish successful leptogenesis. Instead, it suffices if new CP-violating interactions at high energies result in primordial charge asymmetries, which are then reprocessed into a nonvanishing B-L asymmetry by right-handed neutrinos (RHNs) at lower energies. In this paper, we study this novel mechanism known as "wash-in leptogenesis", utilizing axion inflation as the source of high-scale CP violation. We specifically consider axion inflation coupled to the Standard Model hypercharge sector, which results in the dual production of hypermagnetic helicity and fermionic charge asymmetries. Although the survival of these charges is endangered by sphaleron processes, magnetic diffusion, and the chiral plasma instability, we find a large range of viable scenarios. We consistently account for RHN flavor effects and coherence among the Standard Model lepton flavors across a wide range of RHN masses. We find a lower bound of 10^(5...9) GeV on the mass of the lightest RHN involved in wash-in leptogenesis, depending on the onset of turbulence in the chiral plasma and the Hubble scale of inflation. Our model is representative of a broader class of new leptogenesis scenarios and suggests interesting observational signatures with regard to intergalactic magnetic fields, primordial black holes, and gravitational waves.

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Formation of primordial black holes after Starobinsky inflation

Published Paper #: 1089

Authors:, Daniel Frolovsky, Sergei V. Ketov, Sultan Saburov,

Journal: Modern Physics Letters A (2022) 37, 2250135

url: http://arxiv.org/pdf/2205.00603v4.pdf

Abstract: We adapted the Appleby-Battye-Starobinsky model of $F(R)$ gravity towards describing double cosmological inflation and formation of primordial black holes with masses up to $10^{19}$ g in the single-field model. We found that it is possible to get an enhancement of the power spectrum of scalar curvature perturbations to the level beyond the Hawking (black hole evaporation) limit of $10^{15}$ g, so that the primordial black holes resulting from gravitational collapse of those large primordial perturbations can survive in the present universe and form part of cold dark matter. Our results agree with the current measurements of cosmic microwave background radiation within $3\sigma$ but require fine-tuning of the parameters.

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What if planet 9 has satellites?

Published Paper #: 1088

Authors:, Man Ho Chan,

Journal: ApJ 944, 172 (2023)

url: http://arxiv.org/pdf/2301.13471v1.pdf

Abstract: In the past decade, numerical simulations started to reveal the possible existence of planet 9 in our solar system. The planet 9 scenario can provide an excellent explanation to the clustering in orbital elements for Kuiper Belt objects. However, no optical counterpart has been observed so far to verify the planet 9 scenario. Therefore, some recent studies suggest that planet 9 could be a dark object, such as a primordial black hole. In this article, we show that the probability of capturing large trans-Neptunian objects (TNOs) by planet 9 to form a satellite system in the scattered disk region (between the inner Oort cloud and Kuiper Belt) is large. By adopting a benchmark model of planet 9, we show that the tidal effect can heat up the satellites significantly, which can give sufficient thermal radio flux for observations, even if planet 9 is a dark object. This provides a new indirect way for examining the planet 9 hypothesis and revealing the basic properties of planet 9.

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Constraints on primordial curvature spectrum from primordial black holes   and scalar-induced gravitational waves

Published Paper #: 1087

Authors:, Zhu Yi, Qin Fei,

Journal: Eur. Phys. J. C (2023) 83:82

url: http://arxiv.org/pdf/2210.03641v2.pdf

Abstract: The observational data of primordial black holes and scalar-induced gravitational waves can constrain the primordial curvature perturbation at small scales. We parameterize the primordial curvature perturbation by a broken power law form and find that it is consistent with many inflation models that can produce primordial black holes, such as nonminimal derivative coupling inflation, scalar-tensor inflation, Gauss-Bonnet inflation, and K/G inflation. The constraints from primordial black holes on the primordial curvature power spectrum with the broken power law form are obtained, where the fraction of primordial black holes in dark matter is calculated by the peak theory. Both the real-space top-hat and the Gauss window functions are considered. The constraints on the amplitude of primordial curvature perturbation with Gauss window function are around three times larger than those with real-space top-hat window function. The constraints on the primordial curvature perturbation from the NANOGrav 12.5yrs data sets are displayed, where the NANOGrav signals are assumed as the scalar-induced gravitational waves, and only the first five frequency bins are used.

Keywords: ::

The Interplay between the Dark Matter Axion and Primordial Black Holes

Published Paper #: 1086

Authors:, Kratika Mazde, Luca Visinelli,

Journal: JCAP 2301, 021 (2023)

url: http://arxiv.org/pdf/2209.14307v2.pdf

Abstract: If primordial black holes (PBHs) had come to dominate the energy density of the early Universe when oscillations in the axion field began, we show that the relic abundance and expected mass range of the QCD axion would be greatly modified. Since the QCD axion is a potential candidate for dark matter (DM), we refer to it as the DM axion. We predominantly explore PBHs in the mass range $(10^6 - 5\times 10^8)\,$g. We investigate the relation between the relic abundance of DM axions and the parameter space of PBHs. We numerically solve the set of Boltzmann equations, that governs the cosmological evolution during both radiation and PBH-dominated epochs, providing the bulk energy content of the early Universe. We further solve the equation of motion of the DM axion field to obtain its present abundance. Alongside non-relativistic production mechanisms, light QCD axions are generated from evaporating PBHs through the Hawking mechanism and could make up a fraction of the dark radiation (DR). If the QCD axion is ever discovered, it will give us insight into the early Universe and probe into the physics of the PBH-dominated era. We estimate the bounds on the model from DR axions produced via PBH evaporation and thermal decoupling, and we account for isocurvature bounds for the period of inflation where the Peccei-Quinn symmetry is broken. We assess the results obtained against the available CMB data and we comment on the forecasts from gravitational wave searches. We briefly state the consequences of PBH accretion and the uncertainties this may further add to cosmology and astroparticle physics modeling.

Keywords: ::

Enhancing gravitational wave anisotropies with peaked scalar sources

Published Paper #: 1085

Authors:, Ema Dimastrogiovanni, Matteo Fasiello, Ameek Malhotra, Gianmassimo Tasinato,

Journal: JCAP01(2023)018

url: http://arxiv.org/pdf/2205.05644v2.pdf

Abstract: Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments.

Keywords: ::

Testing primordial black hole and measuring the Hubble constant with   multiband gravitational-wave observations

Published Paper #: 1084

Authors:, Lang Liu, Xing-Yu Yang, Zong-Kuan Guo, Rong-Gen Cai,

Journal: JCAP01(2023)006

url: http://arxiv.org/pdf/2112.05473v3.pdf

Abstract: There exist two kinds of stochastic gravitational-wave backgrounds associated with the primordial curvature perturbations. One is called induced gravitational wave due to the nonlinear coupling of curvature perturbations to tensor perturbations, while the other is produced by coalescences of binary primordial black holes formed when the large amplitude curvature perturbations reenter the horizon in the radiation dominant era. In this paper we find a quite useful relation for the peak frequencies of these two stochastic gravitational-wave backgrounds. This relation can not only offer a smoking-gun criterion for the existence of primordial black holes, but also provide a method for measuring the Hubble constant $H_0$ by multiband observations of the stochastic gravitational-wave backgrounds.

Keywords: ::

Compact Binary Merger Rate in Dark-Matter Spikes

Published Paper #: 1083

Authors:, Saeed Fakhry, Zahra Salehnia, Azin Shirmohammadi, Mina Ghodsi Yengejeh, Javad T. Firouzjaee,

Journal: The Astrophysical Journal (2023)

url: http://arxiv.org/pdf/2301.02349v2.pdf

Abstract: Nowadays, the existence of supermassive black holes (SMBHs) in the center of galactic halos is almost confirmed. An extremely dense region referred to as dark-matter spike is expected to form around central SMBHs as they grow and evolve adiabatically. In this work, we calculate the merger rate of compact binaries in dark-matter spikes while considering halo models with spherical and ellipsoidal collapses. Our findings exhibit that ellipsoidal-collapse dark matter halo models can potentially yield the enhancement of the merger rate of compact binaries. Finally, our results confirm that the merger rate of primordial black hole binaries is consistent with the results estimated by the LIGO-Virgo detectors, while such results can not be realized for primordial black hole-neutron star binaries.

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Highly non-Gaussian tails and primordial black holes from single-field   inflation

Published Paper #: 1082

Authors:, Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhou,

Journal: Journal of Cosmology and Astroparticle Physics 12(2022), 034

url: http://arxiv.org/pdf/2207.11910v3.pdf

Abstract: For primordial perturbations, deviations from Gaussian statistics on the tail of the probability distribution can be associated with non-perturbative effects of inflation. In this paper, we present some particular examples in which the tail of the distribution becomes highly non-Gaussian although the statistics remains almost Gaussian in the perturbative regime. We begin with an extension of the ultra-slow-roll inflation that incorporates a transition process, where the inflaton climbs up a tiny potential step at the end of the non-attractor stage before it converges to the slow-roll attractor. Through this example, we identify the key role of the off-attractor behaviour for the upward-step transition, and then extend the analysis to another type of the transition with two slow-roll stages connected by a tiny step. We perform both the perturbative and non-perturbative analyses of primordial fluctuations generated around the step in detail, and show that the tiny but nontrivial transition may affect large perturbations in the tail of the distribution, while the perturbative non-Gaussianity remains small. Our result indicates that the non-Gaussian tails can have rich phenomenology which has been overlooked in conventional analyses. We also study the implications of this non-Gaussian tail for the formation of primordial black holes, and find that their mass fraction can be parametrically amplified by several orders of magnitudes in comparison with the case of the Gaussian distribution. Additionally, we also discuss a mechanism of primordial black holes formation for this upward step inflation model by trapping the inflaton in the bottom of the step.

Keywords: ::

Highly non-Gaussian tails and primordial black holes from single-field   inflation

Published Paper #: 1082

Authors:, Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhou,

Journal: Journal of Cosmology and Astroparticle Physics 12(2022), 034

url: http://arxiv.org/pdf/2207.11910v3.pdf

Abstract: For primordial perturbations, deviations from Gaussian statistics on the tail of the probability distribution can be associated with non-perturbative effects of inflation. In this paper, we present some particular examples in which the tail of the distribution becomes highly non-Gaussian although the statistics remains almost Gaussian in the perturbative regime. We begin with an extension of the ultra-slow-roll inflation that incorporates a transition process, where the inflaton climbs up a tiny potential step at the end of the non-attractor stage before it converges to the slow-roll attractor. Through this example, we identify the key role of the off-attractor behaviour for the upward-step transition, and then extend the analysis to another type of the transition with two slow-roll stages connected by a tiny step. We perform both the perturbative and non-perturbative analyses of primordial fluctuations generated around the step in detail, and show that the tiny but nontrivial transition may affect large perturbations in the tail of the distribution, while the perturbative non-Gaussianity remains small. Our result indicates that the non-Gaussian tails can have rich phenomenology which has been overlooked in conventional analyses. We also study the implications of this non-Gaussian tail for the formation of primordial black holes, and find that their mass fraction can be parametrically amplified by several orders of magnitudes in comparison with the case of the Gaussian distribution. Additionally, we also discuss a mechanism of primordial black holes formation for this upward step inflation model by trapping the inflaton in the bottom of the step.

Keywords: ::

Highly non-Gaussian tails and primordial black holes from single-field   inflation

Published Paper #: 1082

Authors:, Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhou,

Journal: Journal of Cosmology and Astroparticle Physics 12(2022), 034

url: http://arxiv.org/pdf/2207.11910v3.pdf

Abstract: For primordial perturbations, deviations from Gaussian statistics on the tail of the probability distribution can be associated with non-perturbative effects of inflation. In this paper, we present some particular examples in which the tail of the distribution becomes highly non-Gaussian although the statistics remains almost Gaussian in the perturbative regime. We begin with an extension of the ultra-slow-roll inflation that incorporates a transition process, where the inflaton climbs up a tiny potential step at the end of the non-attractor stage before it converges to the slow-roll attractor. Through this example, we identify the key role of the off-attractor behaviour for the upward-step transition, and then extend the analysis to another type of the transition with two slow-roll stages connected by a tiny step. We perform both the perturbative and non-perturbative analyses of primordial fluctuations generated around the step in detail, and show that the tiny but nontrivial transition may affect large perturbations in the tail of the distribution, while the perturbative non-Gaussianity remains small. Our result indicates that the non-Gaussian tails can have rich phenomenology which has been overlooked in conventional analyses. We also study the implications of this non-Gaussian tail for the formation of primordial black holes, and find that their mass fraction can be parametrically amplified by several orders of magnitudes in comparison with the case of the Gaussian distribution. Additionally, we also discuss a mechanism of primordial black holes formation for this upward step inflation model by trapping the inflaton in the bottom of the step.

Keywords: ::

Detection of Early-Universe Gravitational Wave Signatures and   Fundamental Physics

Published Paper #: 1081

Authors:, Robert Caldwell, Yanou Cui, Huai-Ke Guo, Vuk Mandic, Alberto Mariotti, Jose Miguel No, Michael J. Ramsey-Musolf, Mairi Sakellariadou, Kuver Sinha, Lian-Tao Wang, Graham White, Yue Zhao, Haipeng An, Chiara Caprini, Sebastien Clesse, James Cline, Giulia Cusin, Ryusuke Jinno, Benoit Laurent, Noam Levi, Kunfeng Lyu, Mario Martinez, Andrew Miller, Diego Redigolo, Claudia Scarlata, Alexander Sevrin, Barmak Shams Es Haghi, Jing Shu, Xavier Siemens, Daniele A. Steer, Raman Sundrum, Carlos Tamarit, David J. Weir, Bartosz Fornal, Ke-Pan Xie, Fengwei Yang, Siyi Zhou,

Journal: Gen Relativ Gravit 54, 156 (2022)

url: http://arxiv.org/pdf/2203.07972v2.pdf

Abstract: Detection of a gravitational-wave signal of non-astrophysical origin would be a landmark discovery, potentially providing a significant clue to some of our most basic, big-picture scientific questions about the Universe. In this white paper, we survey the leading early-Universe mechanisms that may produce a detectable signal -- including inflation, phase transitions, topological defects, as well as primordial black holes -- and highlight the connections to fundamental physics. We review the complementarity with collider searches for new physics, and multimessenger probes of the large-scale structure of the Universe.

Keywords: ::

Primordial black holes and gravitational waves from dissipation during   inflation

Published Paper #: 1080

Authors:, Guillermo Ballesteros, Marcos A. G. García, Alejandro Pérez Rodríguez, Mathias Pierre, Julián Rey,

Journal: JCAP 12 (2022) 006

url: http://arxiv.org/pdf/2208.14978v2.pdf

Abstract: We study the generation of a localized peak in the primordial spectrum of curvature perturbations from a transient dissipative phase during inflation, leading to a large population of primordial black holes. The enhancement of the power spectrum occurs due to stochastic thermal noise sourcing curvature fluctuations. We solve the stochastic system of Einstein equations for many realizations of the noise and obtain the distribution for the curvature power spectrum. We then propose a method to find its expectation value using a deterministic system of differential equations. In addition, we find a single stochastic equation whose analytic solution helps to understand the main features of the spectrum. Finally, we derive a complete expression and a numerical estimate for the energy density of the stochastic background of gravitational waves induced at second order in perturbation theory. This includes the gravitational waves induced during inflation, during the subsequent radiation epoch and their mixing. Our scenario provides a novel way of generating primordial black hole dark matter with a peaked mass distribution and a detectable stochastic background of gravitational waves from inflation.

Keywords: ::

Probing primordial black holes with anisotropies in stochastic   gravitational-wave background

Published Paper #: 1079

Authors:, Sai Wang, Valeri Vardanyan, Kazunori Kohri,

Journal: Phys. Rev. D 106, 123511 (2022)

url: http://arxiv.org/pdf/2107.01935v3.pdf

Abstract: Primordial black holes, if considered to constitute a significant fraction of cold dark matter, trace the inhomogeneous large-scale structure of the Universe. Consequently, the stochastic gravitational-wave background, originating from incoherent superposition of unresolved signals emitted by primordial black hole binaries, is expected to display anisotropies across the sky. In this work, we investigate the angular correlations of such anisotropies for the first time and demonstrate their difference from the analogous signal produced by astrophysical black hole binaries. We carefully evaluate the associated uncertainties due to shot-noise and cosmic variance, and demonstrate that the studied signal in the low-frequency regime can be differentiated from the signal of astrophysical origin. Our results are particularly promising in the stellar mass-range, where the identification of the merger origin has been particularly challenging.

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The Merger Rate of Primordial Black Hole-Neutron Star Binaries in   Ellipsoidal-Collapse Dark Matter Halo Models

Published Paper #: 1078

Authors:, Saeed Fakhry, Zahra Salehnia, Azin Shirmohammadi, Javad T. Firouzjaee,

Journal: The Astrophysical Journal (2022)

url: http://arxiv.org/pdf/2209.08909v2.pdf

Abstract: Primordial black holes (PBHs), as a potential macroscopic candidate for dark matter, can encounter other compact objects in dark matter halos because of their random distribution. Besides, the detection of gravitational waves (GWs) related to the stellar-mass black hole-neutron star (BH-NS) mergers raises the possibility that the BHs involved in such events may have a primordial origin. In this work, we calculate the merger rate of PBH-NS binaries within the framework of ellipsoidal-collapse dark matter halo models and compare it with the corresponding results derived from spherical-collapse dark matter halo models. Our results exhibit that ellipsoidal-collapse dark matter halo models can potentially amplify the merger rate of PBH-NS binaries in such a way that it is very close to the range estimated by the LIGO-Virgo observations. While spherical-collapse dark matter halo models cannot justify PBH-NS merger events as consistent results with the latest GW data reported by the LIGO-Virgo collaboration. In addition, we calculate the merger rate of PBH-NS binaries as a function of PBH mass and fraction within the context of ellipsoidal-collapse dark matter halo models. The results indicate that PBH-NS merger events with the mass of $(M_{PBH}\le 5 M_{\odot}, M_{NS}\simeq 1.4 M_{\odot})$ will be consistent with the LIGO-Virgo observations if $f_{PBH}\simeq 1$. We also show that to have at least on $(M_{PBH}\simeq 5 M_{\odot}, M_{NS}\simeq 1.4 M_{\odot})$ event in the comoving volume $1 Gpc^{3}$ annually, ellipsoidal-collapse dark matter halo models constrain the abundance of PBHs as $f_{PBH} \geq 0.1$.

Keywords: ::

Primordial Black Holes having Gravitomagnetic Monopole

Published Paper #: 1077

Authors:, Chandrachur Chakraborty, Sudip Bhattacharyya,

Journal: Phys. Rev. D 106, 103028 (2022)

url: http://arxiv.org/pdf/2211.03610v1.pdf

Abstract: A primordial black hole (PBH) is thought to be made of the regular matter or ordinary mass ($M$) only, and hence could have already been decayed due to the Hawking radiation if its initial ordinary mass were $\lesssim 5 \times 10^{11}$ kg. Here, we study the role of gravitomagnetic monopole for the evaporation of PBHs, and propose that the lower energy PBHs (equivalent to ordinary mass $M << 5\times 10^{11}$ kg) could still exist in our present Universe, if it has gravitomagnetic monopole. If a PBH was initially made of both regular matter and gravitomagnetic monopole, the regular matter could decay away due to the Hawking radiation. The remnant gravitomagnetic monopole might not entirely decay, which could still be found as a PBH in the form of the pseudo `mass-energy'. If a PBH with $M \gtrsim 5 \times 10^{11}$ kg is detected, one may not be able to conclude if it has gravitomagnetic monopole. But, a plausible detection of a relatively low energy (equivalent to $2.176 \times 10^{-8}$ kg $< M \lesssim 5\times10^{11}$ kg) PBH in future may imply the existence of a gravitomagnetic monopole PBH, which may or may not contain the ordinary mass.

Keywords: ::

NANOGrav Signal from the End of Inflation and the LIGO Mass and Heavier   Primordial Black Holes

Published Paper #: 1076

Authors:, Amjad Ashoorioon, Kazem Rezazadeh, Abasalt Rostami,

Journal: Phys. Lett. B 835 (2022) 137542. Phys. Lett. B 835 (2022) 137542.
 Phys. Lett. B 835 (2022) 137542. Phys. Lett. B 835 (2022) 137542

url: http://arxiv.org/pdf/2202.01131v3.pdf

Abstract: Releasing the 12.5-year pulsar timing array data, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported the evidence for a stochastic common-spectrum which would herald the detection of a stochastic gravitational wave background (SGWB) for the first time. We investigate if the signal could be generated from the end of a $\sim 10$ MeV but still phenomenologically viable double-field inflation when the field configuration settles to its true vacuum. During the double-field inflation at such scales, bubbles of true vacuum that can collapse to LIGO mass and heavier primordial black holes form. We show that only when this process happens with a first-order phase transition, the produced gravitational wave spectrum can match with the NANOGrav acclaimed SGWB signal. We show that the produced gravitational wave spectrum matches the NANOGrav SGWB signal only when this process happens through a first-order phase transition. Using LATTICEEASY, we also examine the previous observation in the literature that by lowering the scale of preheating, despite the shift of the peak frequency of the gravitational wave profile to smaller values, the amplitude of the SGWB could be kept almost constant. We notice that this observation breaks down at the preheating scale, $M\lesssim 10^{-14}~m_{{}_{\rm Pl}}$.

Keywords: ::

Constraining PBH mass distributions from 21cm brightness temperature   results and an analytical mapping between probability distribution of 21cm   signal and PBH masses

Published Paper #: 1075

Authors:, Upala Mukhopadhyay, Debasish Majumdar, Ashadul Halder,

Journal: JCAP 10, 099 (2022)

url: http://arxiv.org/pdf/2203.13008v2.pdf

Abstract: The evaporation of Primordial Black Hole (PBH) via Hawking radiation influences the evolution of Inter Galactic Medium by heating up the latter and consequently affects the 21cm signal originated from the neutral Hydrogen atoms. In this work, we have considered EDGES observational data of 21cm line corresponding to cosmic dawn era to constrain the mass and the abundance of PBHs. In this context, two different PBH mass distributions namely, power law and lognormal mass distributions are considered to estimate the effects of PBH evaporation on the 21cm brightness temperature $T_{21}$. In addition to these two mass distributions, different monochromatic masses are also considered. The impacts of Dark Matter - baryon interactions on $T_{21}$ are also considered in this work along with the influences of PBH evaporation. Furthermore, adopting different monochromatic masses for PBHs, an attempt has been made to formulate a distribution for PBH masses by associating a probability weightage of the $T_{21}$ values (at $z \sim 17.2$), within the range given by EDGES experiment, with the calculated $T_{21}$ values for each of the PBH mass values. The distribution best suited for the present purpose is found to be a combination of an error function and Owen function. Allowed contours in the parameter space of (initial PBH mass-dark matter mass) are obtained.

Keywords: ::

PBH assisted search for QCD axion dark matter

Published Paper #: 1074

Authors:, Gongjun Choi, Enrico D. Schiappacasse,

Journal: JCAP 09 (2022) 072

url: http://arxiv.org/pdf/2205.02255v2.pdf

Abstract: The entropy production prior to BBN era is one of ways to prevent QCD axion with the decay constant $F_{a}\in[10^{12}{\rm GeV},10^{16}{\rm GeV}]$ from overclosing the universe when the misalignment angle is $\theta_{\rm i}=\mathcal{O}(1)$. As such, it is necessarily accompanied by an early matter-dominated era (EMD) provided the entropy production is achieved via the decay of a heavy particle. In this work, we consider the possibility of formation of primordial black holes during the EMD era with the assumption of the enhanced primordial scalar perturbation on small scales ($k>10^{4}{\rm Mpc}^{-1}$). In such a scenario, it is expected that PBHs with axion halo accretion develop to ultracompact minihalos (UCMHs). We study how UCMHs so obtained could be of great use in the experimental search for QCD axion dark matter with $F_{a}\in[10^{12}{\rm GeV},10^{16}{\rm GeV}]$.

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Non-Gaussianity effects on the primordial black hole abundance for   sharply-peaked primordial spectrum

Published Paper #: 1073

Authors:, Takahiko Matsubara, Misao Sasaki,

Journal: JCAP 10 (2022) 094

url: http://arxiv.org/pdf/2208.02941v2.pdf

Abstract: We perturbatively study the effect of non-Gaussianities on the mass fraction of primordial black holes (PBHs) at the time of formation by systematically taking its effect into account in the one-point probability distribution function of the primordial curvature perturbation. We focus on the bispectrum and trispectrum and derive formulas that describe their effects on the skewness and kurtosis of the distribution function. Then considering the case of narrowly peaked spectra, we obtain simple formulas that concisely express the effect of the bi- and trispectra. In particular, together with the $g_{\rm NL}$ and $\tau_{\rm NL}$ parameters of the trispectrum, we find that non-Gaussianity parameters for various types of the bispectrum are linearly combined to give an effective parameter, $f_{\rm NL}^{\rm eff}$, that determines the PBH mass fraction in the narrow spectral shape limit.

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Gravitational waves induced from primordial black hole fluctuations: The   effect of an extended mass function

Published Paper #: 1072

Authors:, Theodoros Papanikolaou,

Journal: JCAP 10 (2022) 089

url: http://arxiv.org/pdf/2207.11041v2.pdf

Abstract: The gravitational potential of initially Poisson distributed primordial black holes (PBH) can induce a stochastic gravitational-wave background (SGWB) at second order in cosmological perturbation theory. This SGWB was previously studied in the context of general relativity (GR) and modified gravity setups by assuming a monochromatic PBH mass function. Here we extend the previous analysis in the context of GR by studying the aforementioned SGWB within more physically realistic regimes where PBHs have different masses. In particular, starting from a power-law cosmologically motivated primordial curvature power spectrum with a running spectral index we extract the extended PBH mass function and the associated to it PBH gravitational potential which acts as the source of the scalar induced SGWB. At the end, by taking into account the dynamical evolution of the PBH gravitational potential during the transition from the matter era driven by PBHs to the radiation era we extract the respective GW signal today. Interestingly, in order to trigger an early PBH-dominated era and avoid the GW constraints at BBN we find that the running of the spectral index $\alpha_\mathrm{s}$ of our primordial curvature power spectrum should be within the narrow range $\alpha_\mathrm{s}\in[3.316,3.355]\times 10^{-3}$ while at the same time the GW signal is found to be potentially detectable by LISA.

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Primordial non-Guassianity in inflation with gravitationally enhanced   friction

Published Paper #: 1071

Authors:, Li-Yang Chen, Hongwei Yu, Puxun Wu,

Journal: Physical Review D 106, 063537 (2022)

url: http://arxiv.org/pdf/2210.05201v2.pdf

Abstract: The gravitationally enhanced friction can reduce the speed of the inflaton to realize an ultra-slow-roll inflation, which will amplify the curvature perturbations. The amplified perturbations can generate a sizable amount of primordial black holes (PBHs) and induce simultaneously a significant background gravitational waves (SIGWs). In this paper, we investigate the primordial non-Gaussianity of the curvature perturbations in the inflation with gravitationally enhanced friction. We find that when the gravitationally enhanced friction plays a role in the inflationary dynamics, the non-Gaussianity is noticeably larger than that from the standard slow-roll inflation. During the regime in which the power spectrum of the curvature perturbations is around its peak, the non-Gaussianity parameter changes from negative to positive. When the power spectrum is at its maximum, the non-Gaussianity parameter is near zero ($\sim \mathcal{O}(0.01)$). Furthermore, the primordial non-Gaussianity promotes the formation of PBHs, while its effect on SIGWs is negligible.

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Primordial Black-Hole Dark Matter via Warm Natural Inflation

Published Paper #: 1070

Authors:, Miguel Correa, Mayukh R. Gangopadhyay, Nur Jaman, Grant J. Mathews,

Journal: Physics Letters B 835 (2022) 137510

url: http://arxiv.org/pdf/2207.10394v2.pdf

Abstract: We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range ($10^{-16} -10^{-11}M_{\odot}$) where it can account for all of the the dark matter content of the universe while satisfying observational constraints.

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Primordial black hole formation for an anisotropic perfect fluid:   Initial conditions and estimation of the threshold

Published Paper #: 1069

Authors:, Ilia Musco, Theodoros Papanikolaou,

Journal: Phys.Rev.D 106 (2022) 8, 083017

url: http://arxiv.org/pdf/2110.05982v4.pdf

Abstract: This work investigates the formation of primordial black holes within a radiation fluid with an anisotropic pressure. We focus our attention on the initial conditions describing cosmological perturbations in the super horizon regime, using a covariant form of the equation of state in terms of pressure and energy density gradients. The effect of the anisotropy is to modify the initial shape of the cosmological perturbations with respect to the isotropic case. Using the dependence of the threshold $\delta_\mathrm{c}$ for primordial black holes with respect to the shape of cosmological perturbations, we estimate here how the threshold is varying with respect to the amplitude of the anisotropy. If this variation is large enough it could lead to a significant variation of the abundance of PBHs.

Keywords: ::

Global 21-cm brightness temperature in viscous dark energy models

Published Paper #: 1068

Authors:, Ashadul Halder, Shashank Shekhar Pandey, A. S. Majumdar,

Journal: JCAP 10, 049 (2022)

url: http://arxiv.org/pdf/2207.09177v3.pdf

Abstract: We investigate the global 21-cm brightness temperature in the context of viscous dark energy (VDE) models. The bulk viscosity of dark energy perturbs the Hubble evolution of the Universe which could cool baryons faster, and hence, alter the 21-cm brightness temperature. An additional amount of entropy is also produced as an outcome of the viscous flow. We study the combined contribution of Hawking radiation from primordial black holes, decay and annihilation of particle dark matter and baryon-dark matter scattering in the backdrop of VDE models towards modification of the 21-cm temperature. We obtain bounds on the VDE model parameters which can account for the observational excess of the EDGES experiment ($-500^{+200}_{-500}$ mK at redshift $14<z<20$) due to the interplay of the above effects. Moreover, our analysis yields modified constraints on the dark matter mass and scattering cross-section compared to the case of the $\Lambda$CDM model.

Keywords: ::

The primordial black hole from running curvaton

Published Paper #: 1067

Authors:, Lei-Hua Liu,

Journal: Chin. Phys. C 47 (2023) 1, 015105

url: http://arxiv.org/pdf/2107.07310v5.pdf

Abstract: In light of our previous work \cite{Liu:2019xhn}, we investigate the possibility of the formation of a primordial black hole in the second inflationary process induced by the oscillation of curvaton. By adopting the instability of the Mathieu equation, one could utilize the $\delta$ function to fully describe the power spectrum. Due to the running of curvaton mass, we can simulate the value of abundance of primordial black holes nearly covering all of the mass ranges, in which we have given three special cases. One case could account for the dark matter in some sense since the abundance of a primordial black hole is about $75\%$. At late times, the relic of exponential potential could be approximated to a constant of the order of cosmological constant dubbed as a role of dark energy. Thus, our model could unify dark energy and dark matter from the perspective of phenomenology. Finally, it sheds new light on exploring Higgs physics.

Keywords: ::

Electromagnetic Accelerating Universe

Published Paper #: 1066

Authors:, Paul H. Frampton,

Journal: Physics Letter B835, 137480 (2022)

url: http://arxiv.org/pdf/2210.10632v1.pdf

Abstract: In recent work we have extended the theory that dark matter is composed of primordial black hole (PBHs) to extremely high masses and made an assumption that the holographic entropy bound is saturated. Astrophysicists have recently suggested that PBHs are formed with electric charges Q, retain their charges for the age of the universe, all charges have the same sign, and Q/M increases with mass M. Adopting these assumptions and using an approximate formula relating Q and M, it is here suggested that, for PBHs with over a trillion solar masses, Coulomb repulsion can exceed gravitational attraction and that electromagnetic properties of dark matter are a possible cause for the observed accelerated cosmological expansion.

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Evolution of primordial black holes in an adiabatic FLRW universe with   gravitational particle creation

Published Paper #: 1065

Authors:, Subhajit Saha, Abdulla Al Mamon, Somnath Saha,

Journal: General Relativity and Gravitation 54, 122 (2022)

url: http://arxiv.org/pdf/2202.09794v2.pdf

Abstract: We study the evolution of primordial black holes (PBHs) in an adiabatic FLRW universe with dissipation due to bulk viscosity which is considered to be in the form of gravitational particle creation. Assuming that the process of evaporation is quite suppressed during the radiation era, we obtain an analytic solution for the evolution of PBH mass by accretion during this era, subject to an initial condition. We also obtain an upper bound on the accretion efficiency $\epsilon$ for $a \sim a_r$, where $a_r$ is the point of transition from the early de Sitter era to the radiation era. Furthermore, we obtain numerical solutions for the mass of a hypothetical PBH with initial mass 100 g assumed to be formed at an epoch when the value of the Hubble parameter was, say, 1 km/s/Mpc. We consider three values of the accretion efficiency, $\epsilon=0.23,0.5$, and $0.89$ for our study. The analysis reveals that the mass of the PBH increases rapidly due to the accretion of radiation in the early stages of its evolution. The accretion continues but its rate decreases gradually with the evolution of the Universe. Finally, Hawking radiation comes into play and the rate of evaporation surpasses the accretion rate so that the PBH mass starts to decrease. As the Universe grows, evaporation becomes the dominant phenomenon, and the mass of the PBH decreases at a faster rate. As argued by Debnath and Paul, the evaporated mass of the PBHs might contribute towards the dark energy budget of the late Universe.

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Probing Ultra-light Primordial Black Holes as a Dark Matter Candidate

Published Paper #: 1064

Authors:, Anupam Ray,

Journal: Springer Proceedings in Physics 277 (2022) 635-638

url: http://arxiv.org/pdf/2210.00072v2.pdf

Abstract: Dark Matter (DM) is omnipresent in our universe. Despite its abundance, the microscopic identity of DM still remains a mystery. Primordial black holes (PBHs), possibly formed via gravitational collapse of large density perturbations in the early universe, are one of the earliest proposed and viable DM candidates. Recent studies indicate that PBHs can make up a large or even entire fraction of the DM density for a wide range of masses. Here, we briefly review the observational constraints on PBHs as DM, concentrating on the ultra-light mass window. Ultra-light PBHs emit particles via Hawking radiation and can be probed by observing such Hawking evaporated particles in various space as well as ground based detectors. We also outline how next-generation gamma ray telescopes can set a stringent exclusion limit on ultra-light PBH DM by probing low energy photons.

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Inflation with two-form field: the production of primordial black holes   and gravitational waves

Published Paper #: 1063

Authors:, Tomohiro Fujita, Hiromasa Nakatsuka, Ippei Obata, Sam Young,

Journal: JCAP 09 (2022) 017

url: http://arxiv.org/pdf/2202.02401v2.pdf

Abstract: Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space-based laser interferometers.

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Massive neutrino self-interactions and inflation

Published Paper #: 1062

Authors:, Shouvik Roy Choudhury, Steen Hannestad, Thomas Tram,

Journal: JCAP10(2022)018

url: http://arxiv.org/pdf/2207.07142v3.pdf

Abstract: Certain inflationary models like Natural inflation (NI) and Coleman-Weinberg inflation (CWI) are disfavoured by cosmological data in the standard $\Lambda\textrm{CDM}+r$ model (where $r$ is the scalar-to-tensor ratio), as these inflationary models predict the regions in the $n_s-r$ parameter space that are excluded by the cosmological data at more than 2$\sigma$ (here $n_s$ is the scalar spectral index). The same is true for single field inflationary models with an inflection point that can account for all or majority of dark matter in the form of PBHs (primordial black holes). Cosmological models incorporating strongly self-interacting neutrinos (with a heavy mediator) are, however, known to prefer lower $n_s$ values compared to the $\Lambda\rm CDM$ model. Considering such neutrino self-interactions can, thus, open up the parameter space to accommodate the above inflationary models. In this work, we implement the massive neutrino self-interactions with a heavy mediator in two different ways: flavour-universal (among all three neutrinos), and flavour-specific (involving only one neutrino species). We implement the new interaction in both scalar and tensor perturbation equations of neutrinos. Interestingly, we find that the current cosmological data can support the aforementioned inflationary models at 2$\sigma$ in the presence of such neutrino self-interactions.

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One Small Step for an Inflaton, One Giant Leap for Inflation: a novel   non-Gaussian tail and primordial black holes

Published Paper #: 1061

Authors:, Yi-Fu Cai, Xiao-Han Ma, Misao Sasaki, Dong-Gang Wang, Zihan Zhou,

Journal: Physics Letters B 834 (November 10, 2022): 137461

url: http://arxiv.org/pdf/2112.13836v2.pdf

Abstract: We report a novel prediction from single-field inflation that even a tiny step in the inflaton potential can change our perception of primordial non-Gaussianities of the curvature perturbation. Our analysis focuses on the tail of probability distribution generated by an upward step transition between two stages of slow-roll evolution. The nontrivial background dynamics with off-attractor behavior is identified. By using a non-perturbative $\delta N$ analysis, we explicitly show that a highly non-Gaussian tail can be generated by a tiny upward step, even when the conventional nonlinearity parameters $f_{NL}$, $g_{NL}$, etc. remain small. With this example, we demonstrate for the first time the sensitive dependence of non-perturbative effects on the tail of probability distribution. Our scenario has an inconceivable application to primordial black holes by either significantly boosting their abundance or completely forbidding their appearance.

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Primordial Black Holes from Multifield Inflation with Nonminimal   Couplings

Published Paper #: 1060

Authors:, Sarah R. Geller, Wenzer Qin, Evan McDonough, David I. Kaiser,

Journal: Physical Review D 106, 063535 (2022)

url: http://arxiv.org/pdf/2205.04471v2.pdf

Abstract: Primordial black holes (PBHs) provide an exciting prospect for accounting for dark matter. In this paper, we consider inflationary models that incorporate realistic features from high-energy physics -- including multiple interacting scalar fields and nonminimal couplings to the spacetime Ricci scalar -- that could produce PBHs with masses in the range required to address the present-day dark matter abundance. Such models are consistent with supersymmetric constructions, and only incorporate operators in the effective action that would be expected from generic effective field theory considerations. The models feature potentials with smooth large-field plateaus together with small-field features that can induce a brief phase of ultra-slow-roll evolution. Inflationary dynamics within this family of models yield predictions for observables in close agreement with recent measurements, such as the spectral index of primordial curvature perturbations and the ratio of power spectra for tensor to scalar perturbations. As in previous studies of PBH formation resulting from a period of ultra-slow-roll inflation, we find that at least one dimensionless parameter must be highly fine-tuned to produce PBHs in the relevant mass-range for dark matter. Nonetheless, we find that the models described here yield accurate predictions for a significant number of observable quantities using a smaller number of relevant free parameters.

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Growth of power spectrum due to decrease of sound speed during inflation

Published Paper #: 1059

Authors:, Rongrong Zhai, Hongwei Yu, Puxun Wu,

Journal: Physical Review D 106, 023517 (2022)

url: http://arxiv.org/pdf/2207.12745v2.pdf

Abstract: We study the amplification of the curvature perturbations due to a small sound speed and find that its origin is different completely from that due to the ultraslow-roll inflation. This is because when the sound speed is very small the enhancement of the power spectrum comes from the fact that the curvature perturbations at the scales smaller than the cosmic microwave background (CMB) scale becomes scale-variant, rather than growing that leads to the amplification of the curvature perturbations during the ultraslow-roll inflation. At large scales the power spectrum of the curvature perturbations remains to be scale invariant, which is consistent with the CMB observations, and then it will have a transient $k^2$ growth and finally approach a $k^4$ growth as the scale becomes smaller and smaller. Thus the power spectrum can be enhanced to generate a sizable amount of primordial black holes. Furthermore, when the high order correction in the dispersion relation of the curvature perturbations is considered the growth of the power spectrum of the curvature perturbations has the same origin as that in the case without this correction.

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Primordial Black Holes and Gravitational Waves in Hybrid Inflation with   Chaotic Potentials

Published Paper #: 1058

Authors:, Waqas Ahmed, M. Junaid, Umer Zubair,

Journal: Nuclear Physics B 984 (2022) 115968

url: http://arxiv.org/pdf/2109.14838v2.pdf

Abstract: We study the formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) in a non-supersymmetric model of hybrid inflation with chaotic (polynomial-like) potential, including one-loop radiative corrections. A radiatively corrected version of these models is entirely consistent with Planck's data. By adding non-canonical kinetic energy term in the lagrangian, the inflaton experiences a period of ultra-slow-roll, and the amplitude of primordial power spectrum is enhanced to $O(10^{-2})$. The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. %In the enhancement mechanism we explore two possible extensions by employing a Guassian and a step size kinetic function. A wide mass range of PBHs is realized in our model with the frequencies of scalar induced gravitational waves ranged from nHz to kHz. We present several benchmark points where the PBH mass generated during inflation is around $(1 - 100) \, M_{\odot}$, $(10^{-9} - 10^{-7}) \, M_{\odot}$ and $(10^{-16} - 10^{-11}) \, M_{\odot}$. The PBHs can make up most of the dark matter with masses around $(10^{-16} - 10^{-11}) \, M_{\odot}$ and $(1 - 100) \, M_{\odot}$, and their associated SIGWs can be probed by the upcoming ground and space-based gravitational wave (GW) observatories. The evidence of stochastic process recently reported by NANOGrav may be interpreted as SIGWs associated with the formation of PBHs. These SIGWs may also be tested by future interferometer-type GW observations of SKA, DECIGO, LISA, BBO, TaiJi, TianQin, CE and ET.

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E-models of inflation and primordial black holes

Published Paper #: 1057

Authors:, Daniel Frolovsky, Sergei V. Ketov, Sultan Saburov,

Journal: Frontiers in Physics, 04 October 2022

url: http://arxiv.org/pdf/2207.11878v2.pdf

Abstract: We propose and study the new (generalized) E-type $\alpha$-attractor models of inflation, in order to include formation of primordial black holes (PBHs). The inflaton potential has a near-inflection point where slow-roll conditions are violated, thus leading to large scalar perturbations collapsing to PBHs later. An ultra-slow roll (short) phase exists between two (longer) phases of slow-roll inflation. We numerically investigate the phases of inflation, derive the power spectrum of scalar perturbations and calculate the PBHs masses. For certain values of the parameters, the asteroid-size PBHs can be formed with the masses of $10^{17}\div 10^{19}$ g, beyond the Hawking evaporation limit and in agreement with current CMB observations. Those PBHs are a candidate for (part of) dark matter in the present universe, while the gravitational waves induced by the PBHs formation may be detectable by the future space-based gravitational interferometers.

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Effects of Hawking evaporation on PBH distributions

Published Paper #: 1056

Authors:, Markus R. Mosbech, Zachary S. C. Picker,

Journal: SciPost Phys. 13, 100 (2022)

url: http://arxiv.org/pdf/2203.05743v2.pdf

Abstract: Primordial black holes (PBHs) may lose mass by Hawking evaporation. For sufficiently small PBHs, they may lose a large portion of their formation mass by today, or evaporate completely if they form with mass $M<M_\mathrm{crit}\sim5\times10^{14}~\mathrm{g}$. We investigate the effect of this mass loss on extended PBH distributions, showing that the shape of the distribution is significantly changed between formation and today. We reconsider the $\gamma$-ray constraints on PBH dark matter in the Milky Way center with a correctly `evolved' lognormal distribution, and derive a semi-analytic time-dependent distribution which can be used to accurately project monochromatic constraints to extended distribution constraints. We also derive the rate of black hole explosions in the Milky Way per year, finding that although there can be a significant number, it is extremely unlikely to find one close enough to Earth to observe. Along with a more careful argument for why monochromatic PBH distributions are unlikely to source an exploding PBH population today, we (unfortunately) conclude that we are unlikely to witness any PBH explosions.

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Effects of Hawking evaporation on PBH distributions

Published Paper #: 1056

Authors:, Markus R. Mosbech, Zachary S. C. Picker,

Journal: SciPost Phys. 13, 100 (2022)

url: http://arxiv.org/pdf/2203.05743v2.pdf

Abstract: Primordial black holes (PBHs) may lose mass by Hawking evaporation. For sufficiently small PBHs, they may lose a large portion of their formation mass by today, or evaporate completely if they form with mass $M<M_\mathrm{crit}\sim5\times10^{14}~\mathrm{g}$. We investigate the effect of this mass loss on extended PBH distributions, showing that the shape of the distribution is significantly changed between formation and today. We reconsider the $\gamma$-ray constraints on PBH dark matter in the Milky Way center with a correctly `evolved' lognormal distribution, and derive a semi-analytic time-dependent distribution which can be used to accurately project monochromatic constraints to extended distribution constraints. We also derive the rate of black hole explosions in the Milky Way per year, finding that although there can be a significant number, it is extremely unlikely to find one close enough to Earth to observe. Along with a more careful argument for why monochromatic PBH distributions are unlikely to source an exploding PBH population today, we (unfortunately) conclude that we are unlikely to witness any PBH explosions.

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Rare Events Are Nonperturbative: Primordial Black Holes From   Heavy-Tailed Distributions

Published Paper #: 1055

Authors:, Sina Hooshangi, Mohammad Hossein Namjoo, Mahdiyar Noorbala,

Journal: Phys.Lett.B 834 (2022) 137400

url: http://arxiv.org/pdf/2112.04520v2.pdf

Abstract: In recent years it has been noted that the perturbative treatment of the statistics of fluctuations may fail to make correct predictions for the abundance of primordial black holes (PBHs). Moreover, it has been shown in some explicit single-field examples that the nonperturbative effects may lead to an exponential tail for the probability distribution function (PDF) of fluctuations responsible for PBH formation -- in contrast to the PDF being Gaussian, as suggested by perturbation theory. In this paper, we advocate that the so-called $\delta N$ formalism can be considered as a simple, yet effective, tool for the nonperturbative estimate of the tail of the PDF. We discuss the criteria a model needs to satisfy so that the results of the classical $\delta N$ formalism can be trusted and most possible complications due to the quantum nature of fluctuations can be avoided. As a proof of concept, we then apply this method to a simple example and show that the tail of the PDF can be even {\it heavier} than exponential, leading to a significant enhancement of the PBH formation probability, compared with the predictions of the perturbation theory. Our results, along with other related findings, motivate the invention of new, nonperturbative methods for the problem and open up new ideas on generating PBHs with notable abundance.

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Multiple Field Ultra Slow Roll Inflation: Primordial Black Holes From   Straight Bulk And Distorted Boundary

Published Paper #: 1054

Authors:, Sina Hooshangi, Alireza Talebian, Mohammad Hossein Namjoo, Hassan Firouzjahi,

Journal: Phys.Rev.D 105 (2022) 8, 083525

url: http://arxiv.org/pdf/2201.07258v2.pdf

Abstract: We study a model of two-field ultra-slow-roll (USR) inflation bounded by a curve in the field space. Curvature perturbations and non-Gaussianities can be enhanced both during the USR phase and from the inhomogeneities at the boundary. We employ the full non-linear $\delta N$ formalism to calculate the probability distribution function (PDF) for curvature perturbation non-perturbatively and show that the non-linear effects can significantly enhance the abundance of the primordial black holes (PBHs). For large curvature perturbations, the PDF has a universal exponential tail, but for the intermediate values, the PDF -- and, therefore, the abundance of the PBHs -- depend sensitively on the geometry of the boundary.

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Non-Gaussianity and Secondary Gravitational Waves from Primordial Black   Holes Production in $α$-attractor Inflation

Published Paper #: 1053

Authors:, Kazem Rezazadeh, Zeinab Teimoori, Saeid Karimi, Kayoomars Karami,

Journal: Eur. Phys. J. C 82, 758 (2022)

url: http://arxiv.org/pdf/2110.01482v2.pdf

Abstract: We study the non-Gaussianity and secondary Gravitational Waves (GWs) in the process of the Primordial Black Holes (PBHs) production from inflation. In our work, we focus on the $\alpha$-attractor inflation model in which a tiny bump in the inflaton potential enhances the amplitude of the curvature perturbations at some scales and consequently leads to the PBHs production with different mass scales. We implement the computational code BINGO which calculates the non-Gaussianity parameter in different triangle configurations. Our examination implies that in this setup, the non-Gaussianity gets amplified significantly in the equilateral shape around the scales in which the power spectrum of the scalar perturbations undergoes a sharp declination. The imprints of these non-Gaussianities can be probed in the scales corresponding to the BBN and $\mu$-distortion events, or in smaller scales, and detection of such signatures in the future observations may confirm the idea of our model for the generation of PBHs or rule it out. Moreover, we investigate the secondary GWs in this framework and show that in our model, the peak of the present fractional energy density is obtained as $\Omega_{\rm GW0} \sim 10^{-8}$ at different frequencies which depends on the model parameters. These results lie well within the sensitivity region of some GWs detectors at some frequencies, and therefore the observational compatibility of our model can be evaluated by the forthcoming data from these detectors. We further provide some estimations for the tilts of the induced GWs spectrum in the different intervals of frequency, and demonstrate that the spectrum obeys the power-law relation $\Omega_{\rm GW0}\sim f^{n}$ in those frequency bands.

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A Robust Test of the Existence of Primordial Black Holes in Galactic   Dark Matter Halos

Published Paper #: 1052

Authors:, Marek Abramowicz, Michal Bejger, Andrzej Udalski, Maciek Wielgus,

Journal: The Astrophysical Journal Letters 935, L28 (2022)

url: http://arxiv.org/pdf/2206.13335v2.pdf

Abstract: If very low mass primordial black holes (PBH) within the asteroid/moon-mass range indeed reside in galactic dark matter halos, they must necessarily collide with galactic neutron stars (NSs). These collisions must, again necessarily, form light black holes (LBHs) with masses of typical NSs, $M_{\rm LBH} \approx \,1-2\,M_{\odot}$. LBHs may be behind events already detected by ground-based gravitational-wave detectors (GW170817, GW190425, and others such as a mixed stellar black hole-neutron star mass event GW191219_163120), and most recently by microlensing (OGLE-BLG-2011-0462). Although the status of these observations as containing LBHs is not confirmed, there is no question that gravitational-wave detectors and microlensing are in principle and in practice capable of detecting LBHs. We have calculated the creation rate of LBHs resulting from these light primordial black hole collisions with neutron stars. On this basis, we claim that if improved gravitational-wave detectors and microlensing statistics of the LBH events would indicate that the number of LBHs is significantly lower that what follows from the calculated creation rate, then this would be an unambiguous proof that there is no significant light PBH contribution to the galactic dark matter halos. Otherwise, if observed and calculated numbers of LBHs roughly agree, then the hypothesis of primordial black hole existence gets strong observational support, and in addition their collisions with neutron stars may be considered a natural creation channel for the LBHs, solving the problem of their origin, as it is known that they cannot be a product of standard stellar evolution.

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Two populations of LIGO-Virgo black holes

Published Paper #: 1051

Authors:, Gert Hütsi, Martti Raidal, Ville Vaskonen, Hardi Veermäe,

Journal: JCAP 03 (2021) 068

url: http://arxiv.org/pdf/2012.02786v2.pdf

Abstract: We analyse the LIGO-Virgo data, including the recently released GWTC-2 dataset, to test a hypothesis that the data contains more than one population of black holes. We perform a maximum likelihood analysis including a population of astrophysical black holes with a truncated power-law mass function whose merger rate follows from star formation rate, and a population of primordial black holes for which we consider log-normal and critical collapse mass functions. We find that primordial black holes alone are strongly disfavoured by the data, while the best fit is obtained for the template combining astrophysical and primordial merger rates. Alternatively, the data may hint towards two different astrophysical black hole populations. We also update the constraints on primordial black hole abundance from LIGO-Virgo observations finding that in the $2-400M_\odot$ mass range they must comprise less than 0.2% of dark matter.

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Correlated signals of first-order phase transitions and primordial black   hole evaporation

Published Paper #: 1050

Authors:, Danny Marfatia, Po-Yan Tseng,

Journal: JHEP 2208:001 (2022)

url: http://arxiv.org/pdf/2112.14588v3.pdf

Abstract: Fermi balls produced in a cosmological first-order phase transition may collapse to primordial black holes (PBHs) if the fermion dark matter particles that comprise them interact via a sufficiently strong Yukawa force. We show that phase transitions described by a quartic thermal effective potential with vacuum energy, $0.1\lesssim B^{1/4}/{\rm MeV} \lesssim 10^3$, generate PBHs of mass, $10^{-20}\lesssim M_{\rm PBH}/M_\odot \lesssim 10^{-16}$, and gravitational waves from the phase transition (at THEIA/$\mu$Ares) can be correlated with an isotropic extragalactic X-ray/$\gamma$-ray background from PBH evaporation (at AMEGO-X/e-ASTROGAM).

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Inflation, SUSY breaking, and primordial black holes in modified   supergravity coupled to chiral matter

Published Paper #: 1049

Authors:, Yermek Aldabergenov, Andrea Addazi, Sergei V. Ketov,

Journal: Eur. Phys. J. C 82, 681 (2022)

url: http://arxiv.org/pdf/2206.02601v3.pdf

Abstract: We propose a novel model of the modified (Starobinsky-like) old-minimal-type supergravity coupled to a chiral matter superfield, that can {\it simultaneously} describe multi-field inflation, primordial black hole (PBH) formation, dark matter (DM), and spontaneous supersymmetry (SUSY) breaking after inflation in a Minkowski vacuum. The PBH masses in our supergravity model of double slow-roll inflation, with a short phase of "ultra-slow-roll" between two slow-roll phases, are close to $10^{18}$ g. We find that a significant PBH fraction in the allowed mass window can be supplemented by spontaneous SUSY breaking in the vacuum with the gravitino mass close to the scalaron (inflaton) mass M of the order $10^{13}$ GeV. Our supergravity model favors the {\it composite} nature of DM as a mixture of PBH and heavy gravitinos as the lightest SUSY particles. The composite DM significantly relaxes fine-tuning needed for the whole PBH-DM. The PBH-DM fraction is derived, and the second-order gravitational wave background induced by the enhanced scalar perturbations is calculated. Those gravitational waves may be accessible by the future space-based gravitational interferometers.

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On the detectability of gravitational waves from primordial black holes   orbiting Sgr A*

Published Paper #: 1048

Authors:, Stefano Bondani, Francesco Haardt, Alberto Sesana, Enrico Barausse, Massimo Dotti,

Journal: Phys. Rev. D 106, 043015, 2022

url: http://arxiv.org/pdf/2203.05663v2.pdf

Abstract: In this work we characterize the expected gravitational wave signal detectable by the planned space-borne interferometer LISA and the proposed next generation space-borne interferometer $\mu$Ares arising from a population of primordial black holes orbiting Sgr A*, the super-massive black hole at the Galactic center. Assuming that such objects indeed form the entire diffuse mass allowed by the observed orbit of S2 in the Galactic center, under the simplified assumption of circular orbits and monochromatic mass function, we assess the expected signal in gravitational waves, either from resolved and non-resolved sources. We estimate a small but non negligible chance of $\simeq$ 10% of detecting one single 1 M$_{\odot}$ primordial black hole with LISA in a 10-year-long data stream, while the background signal due to unresolved sources would essentially elude any reasonable chance of detection. On the contrary, $\mu$Ares, with a $\simeq$ 3 orders-of-magnitude better sensitivity at $\simeq$ 10$^{-5}$ Hz, would be able to resolve $\simeq$ 140 solar mass primordial black holes in the same amount of time, while the unresolved background should be observable with an integrated signal-to-noise ratio $\gtrsim$ 100. Allowing the typical PBH mass to be in the range 0.01-10 M$_{\odot}$ would increase LISA chance of detection to $\simeq$ 40% towards the lower limit of the mass spectrum. In the case of $\mu$Ares, instead, we find a "sweet spot" just about 1 M$_{\odot}$, a mass for which the number of resolvable events is indeed maximized.

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Thakurta metric does not describe a cosmological black hole

Published Paper #: 1047

Authors:, Tomohiro Harada, Hideki Maeda, Takuma Sato,

Journal: Phys. Lett. B 833 (2022) 137332

url: http://arxiv.org/pdf/2106.06651v5.pdf

Abstract: Recently, the Thakurta metric has been adopted as a model of primordial black holes. We show that the spacetime described by this metric has neither black-hole event horizon nor black-hole trapping horizon and involves the violation of all the standard energy conditions as a solution of the Einstein equation. Therefore, this metric does not describe a cosmological black hole in the early universe. It is pointed out that a contradictory claim by the other group stems from an incorrect choice of sign.

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Enhance Primordial Black Hole Abundance through the Non-linear Processes   around Bounce Point

Published Paper #: 1046

Authors:, Jie-Wen Chen, Mian Zhu, Sheng-Feng Yan, Qing-Qing Wang, Yifu Cai,

Journal: JCAP01 (2023) 015

url: http://arxiv.org/pdf/2207.14532v1.pdf

Abstract: The non-singular bouncing cosmology is an alternative paradigm to inflation, wherein the background energy density vanishes at the bounce point, in the context of Einstein gravity. Therefore, the non-linear effects in the evolution of density fluctuations ($\delta \rho$) may be strong in the bounce phase, which potentially provides a mechanism to enhance the abundance of primordial black holes (PBHs). This article presents a comprehensive illustration for PBH enhancement due to the bounce phase. To calculate the non-linear evolution of $\delta \rho$, the Raychaudhuri equation is numerically solved here. Since the non-linear processes may lead to a non-Gaussian probability distribution function for $\delta \rho$ after the bounce point, the PBH abundance is calculated in a modified Press-Schechter formalism. In this case, the criterion of PBH formation is complicated, due to complicated non-linear evolutionary behavior of $\delta \rho$ during the bounce phase. Our results indicate that the bounce phase indeed has potential to enhance the PBH abundance sufficiently. Furthermore, the PBH abundance is applied to constrain the parameters of bounce phase, providing a complementary to the surveys of cosmic microwave background and large scale structure.

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Signals of primordial black holes at gravitational wave interferometers

Published Paper #: 1045

Authors:, Jonathan Kozaczuk, Tongyan Lin, Ethan Villarama,

Journal: Phys. Rev. D 105, 123023 (2022)

url: http://arxiv.org/pdf/2108.12475v2.pdf

Abstract: Primordial black holes (PBHs) can form as a result of primordial scalar perturbations at small scales. This PBH formation scenario has associated gravitational wave (GW) signatures from second-order GWs induced by the primordial curvature perturbation, and from GWs produced during an early PBH dominated era. We investigate the ability of next generation GW experiments, including BBO, LISA, and CE, to probe this PBH formation scenario in a wide mass range. Measuring the stochastic GW background with GW observatories can constrain the allowed parameter space of PBHs for masses 1e9 - 1e27 g. We also discuss possible GW sources from an unconstrained region where light PBHs (< 1e9 g) temporarily dominate the energy density of the universe before evaporating. We show how PBH formation impacts the reach of GW observatories to the primordial power spectrum and provide constraints implied by existing PBH bounds.

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Primordial Black Hole Merger Rate in Self-Interacting Dark Matter Halo   Models

Published Paper #: 1044

Authors:, Saeed Fakhry, Mahdi Naseri, Javad T. Firouzjaee, Mehrdad Farhoudi,

Journal: Phys. Rev. D 105, 043525 (2022)

url: http://arxiv.org/pdf/2106.06265v5.pdf

Abstract: We study the merger rate of primordial black holes (PBHs) in self-interacting dark matter (SIDM) halo models. To explore a numerical description for the density profile of SIDM halo models, we use the result of a previously performed simulation for SIDM halo models with $\sigma/m=10~{\rm cm^{2}g^{-1}}$. We also propose a concentration-mass-time relation that can explain the evolution of the halo density profile related to SIDM models. Furthermore, we investigate the encounter condition of PBHs that may have been randomly distributed in the medium of dark matter halos. Under these assumptions, we calculate the merger rate of PBHs within each halo considering SIDM halo models and compare the results with that obtained for cold dark matter (CDM) halo models. To do this, we employ the definition of the time after halo virialization as a function of halo mass. We indicate that SIDM halo models for $f_{\rm PBH}>0.32$ can generate sufficient PBH mergers in such a way that those exceed the one resulted from CDM halo models. By considering the spherical-collapse halo mass function, we obtain similar results for the cumulative merger rate of PBHs. Moreover, we calculate the redshift evolution of the PBH total merger rate. To determine a constraint on the PBH abundance, we study the merger rate of PBHs in terms of their fraction and masses and compare those with the black hole merger rate estimated by the Advanced LIGO (aLIGO)-Advanced Virgo (aVirgo) detectors during the third observing run. The results demonstrate that within the context of SIDM halo models, the merger rate of $10~M_{\odot}-10~M_{\odot}$ events can potentially fall within the aLIGO-aVirgo window. We also estimate a relation between the fraction of PBHs and their masses, which is well consistent with our findings.

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Black Hole Metamorphosis and Stabilization by Memory Burden

Published Paper #: 1043

Authors:, Gia Dvali, Lukas Eisemann, Marco Michel, Sebastian Zell,

Journal: Phys. Rev. D 102, 103523 (2020)

url: http://arxiv.org/pdf/2006.00011v3.pdf

Abstract: Systems of enhanced memory capacity are subjected to a universal effect of memory burden, which suppresses their decay. In this paper, we study a prototype model to show that memory burden can be overcome by rewriting stored quantum information from one set of degrees of freedom to another one. However, due to a suppressed rate of rewriting, the evolution becomes extremely slow compared to the initial stage. Applied to black holes, this predicts a metamorphosis, including a drastic deviation from Hawking evaporation, at the latest after losing half of the mass. This raises a tantalizing question about the fate of a black hole. As two likely options, it can either become extremely long lived or decay via a new classical instability into gravitational lumps. The first option would open up a new window for small primordial black holes as viable dark matter candidates.

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The QCD phase transition behind a PBH origin of LIGO/Virgo events?

Published Paper #: 1042

Authors:, Joaquim Iguaz Juan, Pasquale Serpico, Guillermo Franco Abellán,

Journal: JCAP07(2022)009

url: http://arxiv.org/pdf/2204.07027v3.pdf

Abstract: The best-motivated scenario for a sizable primordial black hole (PBH) contribution to the LIGO/Virgo binary black hole mergers invokes the QCD phase transition, which naturally enhances the probability to form PBH with masses of stellar scale. We reconsider the expected mass function associated not only to the QCD phase transition proper, but also the following particle antiparticle annihilation processes, and analyse the constraints on this scenario from a number of observations: The specific pattern in cosmic microwave background (CMB) anisotropies induced by accretion onto PBHs, CMB spectral distortions, gravitational wave searches, and direct counts of supermassive black holes (SMBHs) at high redshift. We find that the scenario is not viable, unless an ad hoc mass evolution for the PBH mass function and a cutoff in power-spectrum very close to the QCD scale are introduced by hand. Despite these negative results, we note that a future detection of coalescing binaries involving sub-solar PBHs has the potential to check the cosmological origin of SMBHs at the $e^\pm$ annihilation epoch, if indeed the PBH mass function is shaped by the changes to the equation of state driven by the thermal history of the universe.

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Induced gravitational waves from the cosmic coincidence

Published Paper #: 1041

Authors:, Shyam Balaji, Joseph Silk, Yi-Peng Wu,

Journal: JCAP 06 (2022) 06, 008

url: http://arxiv.org/pdf/2202.00700v3.pdf

Abstract: The induced gravitational wave (GW) background from enhanced primordial scalar perturbations is one of the most promising observational consequences of primordial black hole (PBH) formation from inflation. We investigate the induced GW spectrum $\Omega_{\textrm{IGW}}$ from single-field inflation in the general ultra-slow-roll (USR) framework, restricting the peak frequency band to be inside $10^{-3}$-$1$ Hz and saturating PBH abundance to comprise all dark matter (DM) in the ultralight asteroid-mass window. By invoking successful baryogenesis driven by USR inflation, we verify the viable parameter space for the specific density ratio between baryons and PBH DM observed today, the so-called "cosmic coincidence." We show that the cosmic coincidence requirement bounds the spectral index $n_{\rm UV}$ in the high frequency limit, $\Omega_{\textrm{IGW}}(f\gg 1)\propto f^{-2n_{\rm UV}}$, into $0 < n_{\rm UV} < 1$, which implies that baryogenesis triggered by USR inflation for PBHs in the mass range of $10^{-16}$-$10^{-12} M_\odot$ can be tested by upcoming Advanced LIGO and Virgo data and next generation experiments such as LISA, Einstein Telescope, TianQin and DECIGO.

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Beyond the Standard Model with BlackHawk v2.0

Published Paper #: 1040

Authors:, Jérémy Auffinger, Alexandre Arbey,

Journal: PoS (CompTools2021) 017

url: http://arxiv.org/pdf/2207.03266v1.pdf

Abstract: We present the new version of BlackHawk v2.0. BlackHawk is a public code designed to compute the Hawking radiation spectra of (primordial) black holes. In the version 2.0, we have added several non-standard BH metrics: charged, higher dimensional and polymerized black holes, in addition to the usual rotating (Kerr) BHs. BlackHawk also embeds some additional scripts and numerical tables that can prove useful in e.g. dark matter studies. We describe these new features and provide some examples of the capabilities of the code. A tutorial for BlackHawk is available on the TOOLS2021 website: https://indico.cern.ch/event/1076291/contributions/4609967/

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On Primordial Black Holes and secondary gravitational waves generated   from inflation with solo/multi-bumpy potential

Published Paper #: 1039

Authors:, Ruifeng Zheng, Jiaming Shi, Taotao Qiu,

Journal: Vol. 46, No. 4 (2022) Chinese physics c 045103

url: http://arxiv.org/pdf/2106.04303v2.pdf

Abstract: It is well known that a primordial black hole (PBH) can be generated in the inflation process of the early universe, especially when the inflation field has a number of non-trivial features that could break the slow-roll condition. In this study, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We determined that the potential with multi-bump can generate power spectra with multi-peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical and elliptical collapses. Finally, we discuss the scalar-induced gravitational waves(SIGWs)generated by linear scalar perturbations at second order.

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Mergers of Maximally Charged Primordial Black Holes

Published Paper #: 1038

Authors:, Konstantinos Kritos, Joseph Silk,

Journal: Phys.Rev.D 105 (2022) 6, 063011

url: http://arxiv.org/pdf/2109.09769v3.pdf

Abstract: Near-extremal primordial black holes stable over cosmological timescales may constitute a significant fraction of the dark matter. Due to their charge the coalescence rate of such black holes is enhanced inside clusters and the non-extremal merger remnants are prone to Hawking evaporation. We demonstrate that if these clusters of near-extremal holes contain a sufficient number of members to survive up to low redshift, the hard photons from continued evaporation begin to dominate the high energy diffuse background. We find that the diffuse photon flux can be observed for a monochromatic mass spectrum of holes lighter than about $10^{12}\rm g$. We place upper bounds on their abundance respecting the current bounds set by gamma ray telescopes. Furthermore, the gravitational wave background induced at the epoch of primordial black hole formation may be detectable by future planned and proposed ground-based and space-borne gravitational wave observatories operating in the mHz to kHz frequency range and can be an important tool for studying light charged primordial black holes over masses in the range $\rm 10^{12}g - 10^{19}g$.

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Doubly peaked induced stochastic gravitational wave background : Testing   baryogenesis from primordial black holes

Published Paper #: 1037

Authors:, Nilanjandev Bhaumik, Anish Ghoshal, Marek Lewicki,

Journal: JHEP 07 (2022) 130

url: http://arxiv.org/pdf/2205.06260v3.pdf

Abstract: Hawking evaporation of primordial black holes (PBHs) can facilitate the generation of matter-antimatter asymmetry. We focus on ultra-low mass PBHs that briefly dominate the universe and evaporate before the big bang nucleosynthesis. We propose a novel test of this scenario by detecting its characteristic doubly peaked gravitational wave (GW) spectrum in future GW observatories. Here the first order adiabatic perturbation from inflation and from the isocurvature perturbations due to PBH distribution, source tensor perturbations in second-order and lead to two peaks in the induced GW background. These resonant peaks are generated at the beginning of standard radiation domination in the presence of a prior PBH-dominated era. This unique GW spectral shape would provide a smoking gun signal of non-thermal baryogenesis from evaporating PBHs, which is otherwise impossible to test in laboratory experiments due to the very high energy scales involved or the feeble interaction of the dark sector with the visible sector.

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Peaks and primordial black holes: the effect of non-Gaussianity

Published Paper #: 1036

Authors:, Sam Young,

Journal: JCAP 05 (2022) 05, 037

url: http://arxiv.org/pdf/2201.13345v2.pdf

Abstract: In light of recent developments in the field, we re-evaluate the effect of local-type non-Gaussianity on the primordial black hole (PBH) abundance (and consequently, upon constraints on the primordial power spectrum arising from PBHs). We apply peaks theory to the full, non-linear compaction, finding that, whilst the effect of non-Gaussianity is qualitatively similar to previous findings, the effect is much less significant. It is found the non-Gaussianity parameters $f_\mathrm{NL}^\mathrm{local}$ and $g_\mathrm{NL}^\mathrm{local}$ typically need to be approximately 1 or 2 orders of magntiude larger respectively to have a similar to that previously found. The effect will be to weaken the dependance of PBH constraints on the primordial power spectrum on the non-Gaussianity parameters, as well as to dramatically weaken constraints on the non-Gaussianity parameters (and/or PBH abundance) arising from the non-observation of dark matter isocurvature modes. We also consider the correlation between the curvature perturbation $\zeta$ and the compaction $C$, finding that, whilst PBHs may form at rare peaks in $C$ these do not necessarily correspond to rare peaks in $\zeta$ - casting some doubt on many of the existing calculations of the PBH abundance.

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Revisiting small-scale fluctuations in $α$-attractor models of   inflation

Published Paper #: 1035

Authors:, Laura Iacconi, Hooshyar Assadullahi, Matteo Fasiello, David Wands,

Journal: JCAP 06 (2022) 007

url: http://arxiv.org/pdf/2112.05092v2.pdf

Abstract: Cosmological $\alpha$-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate $\alpha$-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. We study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space. In the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non geodesic motion in field space. The two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. These enhanced scalar perturbations can lead to primordial black hole (PBH) production and second-order gravitational wave (GW) generation. Due to the existence of universal predictions in $\alpha$-attractors, consistency with current CMB constraints on the large-scale spectral tilt implies that PBHs can only be produced with masses smaller than $10^8\,\text{g}$ and are accompanied by ultra-high frequency GWs, with a peak expected to be at frequencies of order $10\,\text{kHz}$ or above.

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Review on stochastic approach to inflation

Published Paper #: 1034

Authors:, Diego Cruces,

Journal: Universe 2022, 8(6), 334

url: http://arxiv.org/pdf/2203.13852v2.pdf

Abstract: We present a review on the state-of-the-art of the mathematical framework known as stochastic inflation, paying special attention to its derivation and giving references for the readers interested on results coming from the application of the stochastic framework to different inflationary scenarios, especially to those of interest for primordial black hole formation. During the derivation of the stochastic formalism, we will emphasise two aspects in particular: the difference between the separate universe approach and the true long wavelength limit of scalar inhomogeneities and the generically non-Markovian nature of the noises that appear in the stochastic equations.

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Binary black hole mergers from young massive clusters in the   pair-instability supernova mass gap

Published Paper #: 1033

Authors:, Sambaran Banerjee,

Journal: A&A 665, A20 (2022)

url: http://arxiv.org/pdf/2109.14612v4.pdf

Abstract: The recent discovery of the binary black hole (BBH) merger event GW190521, between two black holes (BHs) of $\approx100M_\odot$, and as well as other massive BBH merger events involving BHs within the pair-instability supernova (PSN) mass gap have sparked widespread debate on the origin of such extreme gravitational-wave (GW) events. In this study, I investigate whether dynamical interactions in young massive clusters (YMCs) serves as a viable scenario for assembling PSN-gap BBH mergers. To that end, I explore a grid of 40 new evolutionary models of a representative YMC of initial mass $M_{\rm cl}=7.5\times10^4M_\odot$ ($N\approx1.28\times10^5$) and size $r_h=2$ pc, with all BH progenitor stars being initially in primordial binaries. All cluster models are evolved with the direct, relativistic N-body code NBODY7 incorporating up to date remnant formation, BH natal spin, and general-relativistic (GR) merger recoil schemes. The BBH mergers from these model cluster computations agree well with the masses and effective spin parameters of the GW events in the latest GW transient catalogue (GWTC). In particular, GW190521-like, i.e., $\approx200M_\odot$, low aligned spin events are produced via dynamical merger among BHs derived from star-star merger products. GW190403-like, i.e., PSN-gap, highly asymmetric and aligned events result from mergers involving BHs that are spun up via matter accretion or binary interaction. The present YMC models yield a present day, intrinsic merger rate density of $0-3.8\times10^{-2}{{\rm~yr}^{-1}{\rm Gpc}^{-3}}$ for GW190521-type events. They produce GW190403-like events at a rate within $0-1.6\times10^{-1}{{\rm~yr}^{-1}{\rm Gpc}^{-3}}$ and their total BBH-merger yield within the PSN gap is $0-8.4\times10^{-1}{{\rm~yr}^{-1}{\rm Gpc}^{-3}}$.

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Using LSST Microlensing to Constrain Dark Compact Objects in Spherical   and Disk Configurations

Published Paper #: 1032

Authors:, Harrison Winch, Jack Setford, Jo Bovy, David Curtin,

Journal: ApJ 933 177 (2022)

url: http://arxiv.org/pdf/2012.07136v2.pdf

Abstract: The Legacy Survey of Space and Time (LSST) with the Vera Rubin Observatory will provide strong microlensing constraints on dark compact objects (DCOs) in our Galaxy. However, most current forecasts limit their analysis to Primordial Black Holes (PBH). It is unclear how well LSST microlensing will be able to constrain alternative models of DCOs with different Galactic spatial profile distributions at a subdominant DM fraction. In this work, we investigate how well LSST microlensing will constrain spherical or disk-like Galactic spatial distributions of DCOs, taking into account extended observing times, baryonic microlensing background, and sky distribution of LSST sources. These extensions represent significant improvements over existing microlensing forecasts in terms of both accuracy and versatility. We demonstrate this power by deriving new LSST sensitivity projections for DCOs in spherical and disk-like distributions. We forecast that LSST will be able to constrain one solar mass PBHs to have a DM fraction under $4.1\times10^{-4}$. One-solar-mass objects in a dark disk distribution with the same dimensions as the Galactic disk will be constrained below $3.1\times10^{-4}$, while those with $m = 10^5M_{\odot}$ will be constrained to below $3.4\times10^{-5}$. We find that compressed dark disks can be constrained up to a factor of $\sim10$ better than ones with identical dimensions to the baryonic disk. We also find that dark disks become less tightly constrained when they are tilted with respect to our own disk. This forecasting software is a versatile tool, capable of constraining any model of DCOs in the Milky Way with microlensing, and is made publically available at {https://github.com/HarrisonWinch96/DarkDisk_Microlensing}.

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Testing Super-Heavy Dark Matter from Primordial Black Holes with   Gravitational Waves

Published Paper #: 1031

Authors:, Rome Samanta, Federico R. Urban,

Journal: JCAP06(2022)017

url: http://arxiv.org/pdf/2112.04836v2.pdf

Abstract: Ultra-light primordial black holes with masses $M_{BH}<10^9$~g evaporate before big-bang nucleosynthesis producing all matter fields, including dark matter, in particular super-heavy dark matter: $M_{DM}\gtrsim 10^{10}$ GeV. If the dark matter gets its mass via $U(1)$ symmetry-breaking, the phase transition that gives a mass to the dark matter also produces cosmic strings which radiate gravitational waves. Because the symmetry-breaking scale $\Lambda_{CS}$ is of the same order as $M_{DM}$, the gravitational waves radiated by the cosmic strings have a large enough amplitude to be detectable across all frequencies accessible with current and planned experimental facilities. Moreover, an epoch of early primordial black hole domination introduces a unique spectral break in the gravitational wave spectrum whose frequency is related to the super-heavy dark matter mass. Hence, the features of a stochastic background of primordial gravitational waves could indicate that super-heavy dark matter originated from primordial black holes. In this perspective, the recent finding of a stochastic common-spectrum process across many pulsars by two nano-frequency pulsar timing arrays would fix the dark matter mass to be $3\times 10^{13}~\text{GeV} \lesssim M_{DM} \lesssim 10^{14}~\text{GeV}$. The (non-)detection of a spectral break at $0.2~\text{Hz} \lesssim f_* \lesssim 0.4~\text{Hz}$ would (exclude) substantiate this interpretation of the signal.

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Formation and Abundance of Late Forming Primordial Black Holes as Dark   Matter

Published Paper #: 1030

Authors:, Amlan Chakraborty, Prolay K Chanda, Kanhaiya Lal Pandey, Subinoy Das,

Journal: The Astrophysical Journal, 932:119 (8pp), 2022 June 20

url: http://arxiv.org/pdf/2204.09628v3.pdf

Abstract: We propose a novel mechanism where Primordial Black Hole (PBH) dark matter is formed much later in the history of the universe between the epoch of Big Bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB) photon decoupling. In our setup, one does not need to modify the scale-invariant inflationary power spectra; instead, a late phase transition in strongly interacting fermion-scalar fluid (which naturally occurs around red-shift $ 10^6 \leq \, z_{\scriptscriptstyle T} \, \leq 10^8$ ) creates an instability in the density perturbation as sound speed turns imaginary. As a result, the dark matter perturbation grows exponentially in sub-Compton scales. This follows the immediate formation of early dense dark matter halo, which finally evolves into PBH due to cooling through scalar radiation. We calculate the variance of the density perturbations and PBH fractional abundances $f(M)$ by using a non-monochromatic mass function. We find the peak of our PBH mass function lies between $10^{-16} - 10^{-14}$ solar mass for $ z_{\scriptscriptstyle T} \simeq 10^6$, and thus it can be the entire dark matter of the universe. In PBH formation, one would expect a temporary phase where an attractive scalar balances the Fermi pressure. We numerically confirm that such a state indeed exists, and we find the radius and density profile of the temporary static structure of the dark matter halo, which finally evolves to PBH due to cooling through scalar radiation.

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NANOGrav signal and LIGO-Virgo Primordial Black Holes from the Higgs   field

Published Paper #: 1029

Authors:, Zhu Yi, Zong-Hong Zhu,

Journal: JCAP 05(2022)046

url: http://arxiv.org/pdf/2105.01943v2.pdf

Abstract: We show that the NANOGrav signal can come from the Higgs field with a noncanonical kinetic term in terms of the scalar induced gravitational waves. The scalar induced gravitational waves generated in our model are also detectable by space-based gravitational wave observatories. Primordial black holes with stellar masses that can explain LIGO-Virgo events are also produced. Therefore, the NANOGrav signal and the BHs in LIGO-Virgo events may both originate from the Higgs field.

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Sensitivities on non-spinning and spinning primordial black hole dark   matter with global 21 cm troughs

Published Paper #: 1028

Authors:, Akash Kumar Saha, Ranjan Laha,

Journal: Phys. Rev. D 105, 103026 (2022)

url: http://arxiv.org/pdf/2112.10794v2.pdf

Abstract: Detection of the global 21 cm signal arising from neutral hydrogen can revolutionize our understanding of the standard evolution of the universe after recombination. In addition, it can also be an excellent probe of Dark Matter (DM). Among all the DM candidates, Primordial Black Holes (PBHs) are one of the most well-motivated. Hawking emission from low-mass PBHs can have substantial effect on the thermal and ionization history of the early universe, and that in turn can have an imprint on the global 21 cm signal. Recently EDGES has claimed a global 21 cm signal, though SARAS 3 has rejected that claim. In this work, we investigate the sensitivities on non-spinning and spinning PBHs arising from an EDGES-like measurement of the global 21 cm signal, and find that the sensitivities will be competitive with those arising from other astrophysical observables. We show that the sensitivities can be significantly strengthened depending on various uncertain astrophysical parameters. Besides, we also derive projections on the PBH density from the absorption trough expected during the Dark Ages. Our work shows that the near future unambiguous detection of the global 21 cm absorption troughs can be an excellent probe of PBH DM.

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Q-balls in Non-Minimally Coupled Palatini Inflation and their   Implications for Cosmology

Published Paper #: 1027

Authors:, A. K. Lloyd-Stubbs, J. McDonald,

Journal: Phys.Rev.D 105 (2022), 103532

url: http://arxiv.org/pdf/2112.09121v3.pdf

Abstract: We demonstrate the existence of Q-balls in non-minimally coupled inflation models with a complex inflaton in the Palatini formulation of gravity. We show that there exist Q-ball solutions which are compatible with inflation and we derive a window in the inflaton mass squared for which this is the case. In particular, we confirm the existence of Q-ball solutions with $\phi \sim 10^{17}-10^{18}$ GeV, consistent with the range of field values following the end of slow-roll Palatini inflation. We study the Q-balls and their properties both numerically and in an analytical approximation. The existence of such Q-balls suggests that the complex inflaton condensate can fragment into Q-balls, and that there may be an analogous process for the case of a real inflaton with fragmentation to neutral oscillons. We discuss the possible post-inflationary cosmology following the formation of Q-balls, including an early Q-ball matter domination (eMD) period and the effects of this on the reheating dynamics of the model, gravitational wave signatures which may be detectable in future experiments, and the possibility that Q-balls could lead to the formation of primordial black holes (PBHs). In particular, we show that Palatini Q-balls with field strengths typical of inflaton condensate fragmentation can directly form black holes with masses around 500 kg or more when the self-coupling is $\lambda = 0.1$, resulting in very low (less than 100 GeV) reheating temperatures from black hole decay, with smaller black hole masses and larger reheating temperatures possible for smaller values of $\lambda$. Q-ball dark matter from non-minimally coupled Palatini inflation may also be a direction for future work.

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Ultrahigh-energy Gamma Rays and Gravitational Waves from Primordial   Exotic Stellar Bubbles

Published Paper #: 1026

Authors:, Yi-Fu Cai, Chao Chen, Qianhang Ding, Yi Wang,

Journal: Eur.Phys.J.C 82 (2022) 5, 464

url: http://arxiv.org/pdf/2105.11481v2.pdf

Abstract: We put forward a novel class of exotic celestial objects that can be produced through phase transitions occurred in the primordial Universe. These objects appear as bubbles of stellar sizes and can be dominated by primordial black holes (PBHs). We report that, due to the processes of Hawking radiation and binary evolution of PBHs inside these stellar bubbles, both electromagnetic and gravitational radiations can be emitted that are featured on the gamma-ray spectra and stochastic gravitational waves (GWs). Our results reveal that, depending on the mass distribution, the exotic stellar bubbles consisting of PBHs provide not only a decent fit for the ultrahigh-energy gamma-ray spectrum reported by the recent LHAASO experiment, but also predict GW signals that are expected to be tested by the forthcoming GW surveys.

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Primordial Black Holes from CDM Isocurvature Perturbations

Published Paper #: 1025

Authors:, Samuel Passaglia, Misao Sasaki,

Journal: Phys. Rev. D 105 (2022), 103530

url: http://arxiv.org/pdf/2109.12824v2.pdf

Abstract: We show that primordial black holes can be produced from the collapse of large isocurvature perturbations of the cold dark matter. We develop a novel procedure to compute the resulting black hole abundance by studying matched perturbations of matter-only universes, and we use our procedure to translate observational constraints on black hole abundances into model-independent constraints on cold dark matter isocurvature perturbations over a wide range of scales. The constraint on the typical amplitude of the primordial perturbations weakens slightly slower than linearly on small scales.

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Establishing the Non-Primordial Origin of Black Hole-Neutron Star   Mergers

Published Paper #: 1024

Authors:, Misao Sasaki, Volodymyr Takhistov, Valeri Vardanyan, Ying-li Zhang,

Journal: Astrophys.J. 931 (2022) 1, 2

url: http://arxiv.org/pdf/2110.09509v2.pdf

Abstract: Primordial black holes (PBHs) from the early Universe constitute an attractive dark matter candidate. First detections of black hole-neutron star (BH-NS) candidate gravitational wave events by the LIGO/Virgo collaboration, GW200105 and GW200115, already prompted speculations about non-astrophysical origin. We analyze, for the first time, the total volumetric merger rates of PBH-NS binaries formed via two-body gravitational scattering, finding them to be subdominant to the astrophysical BH-NS rates. In contrast to binary black holes, a significant fraction of which can be of primordial origin, either formed in dark matter halos or in the early Universe, PBH-NS rates cannot be significantly enhanced by contributions preceding star formation. Our findings imply that the identified BH-NS events are of astrophysical origin, even when PBH-PBH events significantly contribute to the GW observations.

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Implications of stochastic effects for primordial black hole production   in ultra-slow-roll inflation

Published Paper #: 1023

Authors:, Daniel G. Figueroa, Sami Raatikainen, Syksy Rasanen, Eemeli Tomberg,

Journal: JCAP05(2022)027

url: http://arxiv.org/pdf/2111.07437v2.pdf

Abstract: We study the impact of stochastic noise on the generation of primordial black hole (PBH) seeds in ultra-slow-roll (USR) inflation with numerical simulations. We consider the non-linearity of the system by consistently taking into account the noise dependence on the inflaton perturbations, while evolving the perturbations on the coarse-grained background affected by the noise. We capture in this way the non-Markovian nature of the dynamics, and demonstrate that non-Markovian effects are subleading. Using the $\Delta N$ formalism, we find the probability distribution $P(\mathcal{R})$ of the comoving curvature perturbation $\mathcal{R}$. We consider inflationary potentials that fit the CMB and lead to PBH dark matter with $i)$ asteroid, $ii)$ solar, or $iii)$ Planck mass, as well as $iv)$ PBHs that form the seeds of supermassive black holes. We find that stochastic effects enhance the PBH abundance by a factor of $\mathcal{O}(10)-\mathcal{O}(10^8)$, depending on the PBH mass. We also show that the usual approximation, where stochastic kicks depend only on the Hubble rate, either underestimates or overestimates the abundance by orders of magnitude, depending on the potential. We evaluate the gauge dependence of the results, discuss the quantum-to-classical transition, and highlight open issues of the application of the stochastic formalism to USR inflation.

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Interstellar Gas Heating by Primordial Black Holes

Published Paper #: 1022

Authors:, Volodymyr Takhistov, Philip Lu, Graciela B. Gelmini, Kohei Hayashi, Yoshiyuki Inoue, Alexander Kusenko,

Journal: JCAP 03 (2022) 017

url: http://arxiv.org/pdf/2105.06099v2.pdf

Abstract: Interstellar gas heating is a powerful cosmology-independent observable for exploring the parameter space of primordial black holes (PBHs) formed in the early Universe that could constitute part of the dark matter (DM). We provide a detailed analysis of the various aspects for this observable, such as PBH emission mechanisms. Using observational data from the Leo T dwarf galaxy, we constrain the PBH abundance over a broad mass-range, $M_{\rm PBH} \sim \mathcal{O}(1) M_{\odot}-10^7 M_{\odot}$, relevant for the recently detected gravitational wave signals from intermediate-mass BHs. We also consider PBH gas heating of systems with bulk relative velocity with respect to the DM, such as Galactic clouds.

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Primordial black holes and secondary gravitational waves from natural   inflation

Published Paper #: 1021

Authors:, Qing Gao, Yungui Gong, Zhu Yi,

Journal: Nucl. Phys. B 969 (2021) 115480

url: http://arxiv.org/pdf/2012.03856v3.pdf

Abstract: The production of primordial black hole (PBH) dark matter (DM) and the generation of scalar induced secondary gravitational waves by using the enhancement mechanism with a peak function in the non-canonical kinetic term in natural inflation is discussed. We show explicitly that the power spectrum for the primordial curvature perturbation can be enhanced at $10^{12}$ Mpc$^{-1}$, $10^{8}$ Mpc$^{-1}$ and $10^{5}$ Mpc$^{-1}$ by adjusting the model parameters. With the enhanced primordial curvature perturbations, we show the production of PBH DM with peak masses around $10^{-13}\ M_{\odot}$, the Earth's mass and the stellar mass, and the generation of scalar induced gravitational waves (SIGWs) with peak frequencies around mHz, $10^{-6}$ Hz and nHz, respectively. The PBHs with the mass scale $10^{-13}\ M_{\odot}$ can make up almost all the DM and the associated SIGWs is testable by spaced based gravitational wave observatory.

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Primordial Black Holes as Dark Matter Candidates

Published Paper #: 1020

Authors:, Bernard Carr, Florian Kuhnel,

Journal: SciPost Phys. Lect. Notes 48 (2022)

url: http://arxiv.org/pdf/2110.02821v3.pdf

Abstract: We review the formation and evaporation of primordial black holes (PBHs) and their possible contribution to dark matter. Various constraints suggest they could only provide most of it in the mass windows $10^{17}$ - $10^{23}\,$g or $10$ - $10^{2}\,M_{\odot}$, with the last possibility perhaps being suggested by the LIGO/Virgo observations. However, PBHs could have important consequences even if they have a low cosmological density. Sufficiently large ones might generate cosmic structures and provide seeds for the supermassive black holes in galactic nuclei. Planck-mass relics of PBH evaporations or stupendously large black holes bigger than $10^{12}\,M_{\odot}$ could also be an interesting dark component.

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Tracing Astrophysical Black Hole Seeds and Primordial Black Holes with   LISA-Taiji Network

Published Paper #: 1019

Authors:, Yuchan Yang, Wen-Biao Han, Qianyun Yun, Peng Xu, Ziren Luo,

Journal: MNRAS 512, 6217 (2022)

url: http://arxiv.org/pdf/2205.00408v1.pdf

Abstract: In this work, we discuss the improvement that the joint network of LISA and Taiji could provide on exploring two kinds of black hole formation mechanisms. For astrophysical origin, we consider light seed and heavy seed scenarios, and generate populations accordingly. We find that the joint network has the potential to observe growing light seeds in the range 15 < z < 20, while single detector can hardly see, which would shed light on the light seeding mechanism. For the heavy seeds, the joint network only improves the signal-to-noise ratio. For primordial origin, we calculate the event rate at z > 20 and detection rates of LISA and the joint network. The joint network expands LISA's horizon towards lower mass end, where the event rate is high, so we have better chance observing primordial black holes with the joint network. We also estimate the parameters using Fisher matrices of LISA and the joint network, and find that the joint network significantly improves the estimation.

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Mass-gap extreme mass ratio inspirals

Published Paper #: 1018

Authors:, Zhen Pan, Zhenwei Lyu, Huan Yang,

Journal: Phys. Rev. D 105, 083005, (2022)

url: http://arxiv.org/pdf/2112.10237v3.pdf

Abstract: In this work, we propose a new subclass of extreme-mass-ratio-inspirals (EMRIs): mass-gap EMRIs, consisting of a compact object in the lower mass gap $\sim (2.5-5) M_\odot$ and a massive black hole (MBH). The mass-gap object (MGO) may be a primordial black hole or produced from a delayed supernova explosion. We calculate the formation rate of mass-gap EMRIs in both the (dry) loss-cone channel and the (wet) active galactic nucleus disk channel by solving Fokker-Planck-type equations for the phase-space distribution. In the dry channel, the mass-gap EMRI rate is strongly suppressed compared to the EMRI rate of stellar-mass black holes (sBHs) as a result of mass segregation effect. In the wet channel, the suppression is roughly equal to the mass ratio of sBHs over MGOs, because the migration speed of a compact object in an active galactic nucleus disk is proportional to its mass. We find that the wet channel is much more promising to produce mass-gap EMRIs observable by spaceborne gravitation wave detectors. (Non-)detection of mass-gap EMRIs may be used to distinguish different supernova explosion mechanisms and constrainthe abundance of primordial black holes around MBHs.

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Revisiting constraints on asymmetric dark matter from collapse in white   dwarf stars

Published Paper #: 1017

Authors:, Heinrich Steigerwald, Valerio Marra, Stefano Profumo,

Journal: Phys. Rev. D 105, 083507 (2022)

url: http://arxiv.org/pdf/2203.09054v3.pdf

Abstract: The runaway collapse phase of a small dark matter cluster inside a white dwarf star encompasses a reversible stage, where heat can be transferred back and forth between nuclear and dark matter. Induced nuclear burning phases are stable and early carbon depletion undermines previous claims of type Ia supernova ignition. Instead, mini black holes are formed at the center of the star that either evaporate or accrete stellar material until a macroscopic sub-Chandrasekhar-mass black hole is formed. In the latter case, a 0.1 to 1 second lasting electromagnetic transient signal can be detected upon ejection of the white dwarf's potential magnetic field. Binary systems that transmute to black holes and subsequently merge emit gravitational waves. Advanced LIGO/Virgo should detect one such sub-Chandrasekhar binary black hole inspiral per year, while future Einstein telescope-like facilities will detect thousands per year. The effective spin parameter distribution is peaked at 0.2 and permits future studies to disentangle from primordial sub-Chandrasekhar black holes. Such signatures are compatible with current direct detection constraints, as well as with neutron star constraints in the case of bosonic dark matter, even though they remain in conflict with the fermionic case for part of the parameter space.

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New evidence for a cosmological distribution of stellar mass primordial   black holes

Published Paper #: 1016

Authors:, M. R. S. Hawkins,

Journal: MNRAS 512, 5706-5714 (2022)

url: http://arxiv.org/pdf/2204.09143v1.pdf

Abstract: In this paper we show that to explain the observed distribution of amplitudes in a large sample of quasar lightcurves, a significant contribution from microlensing is required. This implies the existence of a cosmologically distributed population of stellar mass compact bodies making up a large fraction of the dark matter. Our analysis is based on the lightcurves of a sample of over 1000 quasars, photometrically monitored over a period of 26 years. The intrinsic variations in quasar luminosity are derived from luminous quasars where the quasar accretion disc is too large to be microlensed by stellar mass bodies, and then synthetic lightcurves for the whole sample are constructed with the same statistical properties. We then run microlensing simulations for each quasar with convergence in compact bodies appropriate to the quasar redshift assuming a $\Lambda$CDM cosmology. The synthetic lightcurve is then superimposed on the amplification pattern to incorporate the effects of microlensing. The distribution of the resulting amplitudes can then be compared with observation, giving a very close match. This procedure does not involve optimising parameters or fitting to the data, as all inputs such as lens mass and quasar disc size come from independent observations in the literature. The overall conclusion of the paper is that to account for the distribution of quasar lightcurve amplitudes it is necessary to include the microlensing effects of a cosmologically distributed population of stellar mass compact bodies, most plausibly identified as stellar mass primordial black holes.

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The stochastic gravitational wave background from close hyperbolic   encounters of primordial black holes in dense clusters

Published Paper #: 1015

Authors:, Juan García-Bellido, Santiago Jaraba, Sachiko Kuroyanagi,

Journal: Physics of the Dark Universe 36 (2022), 101009

url: http://arxiv.org/pdf/2109.11376v2.pdf

Abstract: The inner part of dense clusters of primordial black holes is an active environment where multiple scattering processes take place. Some of them give rise from time to time to bounded pairs, and the rest ends up with a single scattering event. The former eventually evolves to a binary black hole (BBH) emitting periodic gravitational waves (GWs), while the latter with a short distance, called close hyperbolic encounters (CHE), emits a strong GW burst. We make the first calculation of the stochastic GW background originating from unresolved CHE sources. Unlike the case for BBH, the low-frequency tail of the SGWB from CHE is sensitive to the redshift dependence of the event rate, which could help distinguish the astrophysical from the primordial black hole contributions. We find that there is a chance that CHE can be tested by third-generation ground-based GW detectors such as Einstein Telescope and Cosmic Explorer.

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The 511 keV Excess and Primordial Black Holes

Published Paper #: 1014

Authors:, Celeste Keith, Dan Hooper,

Journal: Phys. Rev. D 104, 063033 (2021)

url: http://arxiv.org/pdf/2103.08611v2.pdf

Abstract: An excess of 511 keV photons has been detected from the central region of the Milky Way. It has been suggested that the positrons responsible for this signal could be produced through the Hawking evaporation of primordial black holes. After evaluating the constraints from INTEGRAL, COMPTEL, and Voyager 1, we find that black holes in mass range of $\sim(1-4)\times10^{16}$ g could potentially produce this signal if they make up a small fraction of the total dark matter density. Proposed MeV-scale gamma-ray telescopes such as AMEGO or e-ASTROGAM should be able to test this class of scenarios by measuring the diffuse gamma ray emission from the Milky Way's inner halo.

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Reevaluation of the cosmic antideuteron flux from cosmic-ray   interactions and from exotic sources

Published Paper #: 1013

Authors:, Laura Šerkšnytė, Stephan Königstorfer, Philip von Doetinchem, Laura Fabbietti, Diego Mauricio Gomez-Coral, Johannes Herms, Alejandro Ibarra, Thomas Pöschl, Anirvan Shukla, Andrew Strong, Ivan Vorobyev,

Journal: Phys. Rev. D 105, 083021 (2022)

url: http://arxiv.org/pdf/2201.00925v2.pdf

Abstract: Cosmic-ray antideuterons could be a key for the discovery of exotic phenomena in our Galaxy, such as dark-matter annihilations or primordial black hole evaporation. Unfortunately the theoretical predictions of the antideuteron flux at Earth are plagued with uncertainties from the mechanism of antideuteron production and propagation in the Galaxy. We present the most up-to-date calculation of the antideuteron fluxes from cosmic-ray collisions with the interstellar medium and from exotic processes. We include for the first time the antideuteron inelastic interaction cross section recently measured by the ALICE collaboration to account for the loss of antideuterons during propagation. In order to bracket the uncertainty in the expected fluxes, we consider several state-of-the-art models of antideuteron production and of cosmic-ray propagation.

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Dark Matter as dark dwarfs and other macroscopic objects: multiverse   relics?

Published Paper #: 1012

Authors:, Christian Gross, Giacomo Landini, Alessandro Strumia, Daniele Teresi,

Journal: J.HEP 09 (2021) 33

url: http://arxiv.org/pdf/2105.02840v2.pdf

Abstract: First-order phase transitions can leave relic pockets of false vacua and their particles, that manifest as macroscopic Dark Matter. We compute one predictive model: a gauge theory with a dark quark relic heavier than the confinement scale. During the first-order phase transition to confinement, dark quarks remain in the false vacuum and get compressed, forming Fermi balls that can undergo gravitational collapse to stable dark dwarfs (bound states analogous to white dwarfs) near the Chandrasekhar limit, or to primordial black holes.

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Measuring the dark matter environments of black hole binaries with   gravitational waves

Published Paper #: 1011

Authors:, Adam Coogan, Gianfranco Bertone, Daniele Gaggero, Bradley J. Kavanagh, David A. Nichols,

Journal: Phys. Rev. D 105, 043009 (2022)

url: http://arxiv.org/pdf/2108.04154v2.pdf

Abstract: Large dark matter overdensities can form around black holes of astrophysical and primordial origin as they form and grow. This "dark dress" inevitably affects the dynamical evolution of binary systems, and induces a dephasing in the gravitational waveform that can be probed with future interferometers. In this paper, we introduce a new analytical model to rapidly compute gravitational waveforms in presence of an evolving dark matter distribution. We then present a Bayesian analysis determining when dressed black hole binaries can be distinguished from GR-in-vacuum ones and how well their parameters can be measured, along with how close they must be to be detectable by the planned Laser Interferometer Space Antenna (LISA). We show that LISA can definitively distinguish dark dresses from standard binaries and characterize the dark matter environments around astrophysical and primordial black holes for a wide range of model parameters. Our approach can be generalized to assess the prospects for detecting, classifying, and characterizing other environmental effects in gravitational wave physics.

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Primordial black holes and scalar induced gravitational waves from the   $E$ model with a Gauss-Bonnet term

Published Paper #: 1010

Authors:, Fengge Zhang,

Journal: Physical Review D 105, 063539 (2022)

url: http://arxiv.org/pdf/2112.10516v2.pdf

Abstract: We study an inflationary $E$ model with the Gauss-Bonnet coupling, which can enhance the curvature perturbation at small scales and thus produce a significant abundance of primordial black holes (PBHs) and detectable scalar induced gravitational waves (SIGWs). PBHs from the $E$ model with mass $30M_{\odot}$, $10^{-5}M_{\odot}$, and $10^{-12}M_{\odot}$ can explain the LIGO-Virgo events, the ultrashort-timescale microlensing events in the OGLE data, and all dark matter, respectively. SIGWs produced by the $E$ model can account for the recent NANOGrav signal. We also compute the primordial non-Gaussianity and discuss its impact on PBHs and SIGWs. The probability distribution of density contrast is modified to be right-tailed, which we find prompts the formation of PBHs, so that the abundance of PBHs is underestimated with Gaussian approximation. On the contrary, the fractional energy density of SIGWs is hardly affected.

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Primordial black hole formation with full numerical relativity

Published Paper #: 1009

Authors:, Eloy de Jong, Josu C. Aurrekoetxea, Eugene A. Lim,

Journal: JCAP03(2022)029

url: http://arxiv.org/pdf/2109.04896v3.pdf

Abstract: We study the formation of black holes from subhorizon and superhorizon perturbations in a matter dominated universe with 3+1D numerical relativity simulations. We find that there are two primary mechanisms of formation depending on the initial perturbation's mass and geometry -- via $\textit{direct collapse}$ of the initial overdensity and via $\textit{post-collapse accretion}$ of the ambient dark matter. In particular, for the latter case, the initial perturbation does not have to satisfy the hoop conjecture for a black hole to form. In both cases, the duration of the formation the process is around a Hubble time, and the initial mass of the black hole is $M_\mathrm{BH} \sim 10^{-2} H^{-1} M_\mathrm{Pl}^2$. Post formation, we find that the PBH undergoes rapid mass growth beyond the self-similar limit $M_\mathrm{BH}\propto H^{-1}$, at least initially. We argue that this implies that most of the final mass of the PBH is accreted from its ambient surroundings post formation.

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Dark Fluxes from Accreting Black Holes and Direct Detections

Published Paper #: 1008

Authors:, Rong-Gen Cai, Sichun Sun, Bing Zhang, Yun-Long Zhang,

Journal: Eur. Phys. J. C 82, 245 (2022)

url: http://arxiv.org/pdf/2009.02315v2.pdf

Abstract: We discuss the possibility that accreting black hole systems can be sources for dark matter flux through several different mechanisms. We firstly discuss two types of systems: coronal thermal plasmas around supermassive black holes in active galactic nuclei (AGNs), and accretion disks of stellar-mass X-ray black hole binaries (BHBs). We explore how these black hole systems may produce keV light dark matter fluxes and find that the dark fluxes from those sources might be too weak to account for the current XENON1T excess. On the other hand, black holes can be good accelerators to accrete and boost heavy dark matter particles. If considering collisions or dark electromagnetism, those particles can then escape and reach the benchmark speed of 0.1c at the detector. We also extend the black hole mass region to primordial black holes (PBHs) and discuss the possibility of contributing to keV light dark flux via superradiance of PBHs.

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Constraints on ultracompact minihalos from the extragalactic gamma-ray   background observation

Published Paper #: 1007

Authors:, Xing-Fu Zhang, Ji-Gui Cheng, Ben-Yang Zhu, Tian-Ci Liu, Yun-Feng Liang, En-Wei Liang,

Journal: Phys. Rev. D 105, 043011 (2022)

url: http://arxiv.org/pdf/2109.09575v3.pdf

Abstract: Ultracompact minihalo (UCMH) is a special type of dark matter halo with a very steep density profile which may form in the early universe seeded by an overdense region or a primordial black hole. Constraints on its abundance give valuable information on the power spectrum of primordial perturbation. In this work, we update the constraints on the UCMH abundance in the universe using the extragalactic gamma-ray background (EGB) observation. Comparing to previous works, we adopt the updated Fermi-LAT EGB measurement and derive constraints based on a full consideration of the astrophysical contributions. With these improvements, we place constraints on UCMH abundance 1-2 orders of magnitude better than previous results. With the background components considered, we can also attempt to search for possible additional components beyond the known astrophysical contributions.

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Primordial black holes ensued from exponential potential and coupling   parameter in nonminimal derivative inflation model

Published Paper #: 1006

Authors:, Soma Heydari, Kayoomars Karami,

Journal: JCAP03(2022)033

url: http://arxiv.org/pdf/2111.00494v2.pdf

Abstract: Here, Primordial Black Holes (PBHs) creation from exponential potential has been inquired, through gravitationally raised friction emanated from the nonminimal coupling between gravity and field derivative setup. Setting a two-parted exponential function of inflaton field as coupling parameter, and fine-tuning of four parameter cases of our model, we could sufficiently slow down the inflaton owing to high friction during an ultra slow-roll phase. This empowers us to achieve enough enhancement in the amplitude of curvature perturbations power spectra, via numerical solving of Mukhanov-Sasaki equation. Thereafter, we illustrate the generation of four PBHs with disparate masses in RD era, corresponding to our four parameter cases. Two specimens of these PBHs with stellar ${\cal O}(10)M_{\odot}$ and earth ${\cal O}(10^{-6})M_{\odot}$ masses can be appropriate to explicate the LIGO-VIRGO events, and the ultrashort-timescale microlensing events in OGLE data, respectively. Another two cases of PBHs have asteroid masses around ${\cal O}(10^{-13})M_{\odot}$ and ${\cal O}(10^{-15})M_{\odot}$ with abundance of $96\%$ and $95\%$ of the Dark Matter (DM) content of the universe. Furthermore, we scrutinize the induced Gravitational Waves (GWs) ensued from PBHs production in our model. Subsequently, we elucidate that their contemporary density parameter spectra $(\Omega_{\rm GW_0})$ for all predicted cases have acmes which lie in the sensitivity scopes of the GWs detectors, thereupon the verity of our conclusions can be verified in view of deduced data from these detectors. At length, our numerical outcomes exhibit a power-law behavior for the spectra of $\Omega_{\rm GW_0}$ with respect to frequency as $\Omega_{\rm GW_0} (f) \sim (f/f_c)^{n} $ in the proximity of acmes position. As well, in the infrared regime $f\ll f_{c}$, the log-reliant form of power index as $n=3-2/\ln(f_c/f)$ is attained.

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Constraining primordial black holes as dark matter using the global   21-cm signal with X-ray heating and excess radio background

Published Paper #: 1005

Authors:, Shikhar Mittal, Anupam Ray, Girish Kulkarni, Basudeb Dasgupta,

Journal: JCAP 03 (2022) 030

url: http://arxiv.org/pdf/2107.02190v2.pdf

Abstract: Using the global 21-cm signal measurement by the EDGES collaboration, we derive constraints on the fraction of the dark matter that is in the form of primordial black holes (PBHs) with masses in the range $10^{15}$-$10^{17}\,$g. Improving upon previous analyses, we consider the effect of the X-ray heating of the intergalactic medium on these constraints, and also use the full shape of the 21-cm absorption feature in our inference. In order to account for the anomalously deep absorption amplitude, we also consider an excess radio background motivated by LWA1 and ARCADE2 observations. Because the heating rate induced by PBH evaporation evolves slowly, the data favour a scenario in which PBH-induced heating is accompanied by X-ray heating. Also, for the same reason, using the full measurement across the EDGES observation band yields much stronger constraints on PBHs than just the redshift of absorption. We find that 21-cm observations exclude $f_{\mathrm{PBH}} \gtrsim 10^{-9.7}$ at 95% CL for $M_{\mathrm{PBH}}=10^{15}\,$g. This limit weakens approximately as $M_{\mathrm{PBH}}^4$ towards higher masses, thus providing the strongest constraints on ultralight evaporating PBHs as dark matter over the entire mass range $10^{15}$-$10^{17}\,$g. Under the assumption of a simple spherical gravitational collapse based on the Press-Schechter formalism, we also derive bounds on the curvature power spectrum at extremely small scales ($k\sim 10^{15}\,$Mpc$^{-1}$). This highlights the usefulness of global 21-cm measurements, including non-detections, across wide frequency bands for probing exotic physical processes.

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Local temperature distribution in the vicinity of gravitationally bound   objects in the expanding Universe

Published Paper #: 1004

Authors:, P. M. Petryakova, S. G. Rubin,

Journal: Physics of Atomic Nuclei 84, 2021

url: http://arxiv.org/pdf/1910.12071v2.pdf

Abstract: We consider a cluster of Primordial Black Holes which is decoupled from the cosmological expansion (Hubble flow) and this region is heated as compared to the surrounding matter. The increased temperature inside the region can be explained by several mechanisms of Primordial Black Holes formation. We study the temperature dynamics of the heated region of Primordial Black Holes cluster.

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Connecting the Extremes: A Story of Supermassive Black Holes and   Ultralight Dark Matter

Published Paper #: 1003

Authors:, Hooman Davoudiasl, Peter B. Denton, Julia Gehrlein,

Journal: Phys. Rev. Lett. 128, 081101 (2022)

url: http://arxiv.org/pdf/2109.01678v2.pdf

Abstract: The formation of ultra rare supermassive black holes (SMBHs), with masses of $\mathcal O(10^9\,M_\odot)$, in the first billion years of the Universe remains an open question in astrophysics. At the same time, ultralight dark matter (DM) with mass in the vicinity of $\mathcal O(10^{-20}~\text{eV})$ has been motivated by small scale DM distributions. Though this type of DM is constrained by various astrophysical considerations, certain observations could be pointing to modest evidence for it. We present a model with a confining first order phase transition at $\sim 10$ keV temperatures, facilitating production of $\mathcal O(10^9\,M_\odot)$ primordial SMBHs. Such a phase transition can also naturally lead to the implied mass for a motivated ultralight axion DM candidate, suggesting that SMBHs and ultralight DM may be two sides of the same cosmic coin. We consider constraints and avenues to discovery from superradiance and a modification to $N_{\rm eff}$. On general grounds, we also expect primordial gravitational waves -- from the assumed first order phase transition -- characterized by frequencies of $\mathcal O(10^{-12}-10^{-9}~\text{Hz})$. This frequency regime is largely uncharted, but could be accessible to pulsar timing arrays if the primordial gravitational waves are at the higher end of this frequency range, as could be the case in our assumed confining phase transition.

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Broad search for gravitational waves from subsolar-mass binaries through   LIGO and Virgo's third observing run

Published Paper #: 1002

Authors:, Alexander H. Nitz, Yi-Fan Wang,

Journal: Phys. Rev. D 106, 023024 (2022)

url: http://arxiv.org/pdf/2202.11024v1.pdf

Abstract: We present a search for gravitational waves from the coalescence of binaries which contain at least one subsolar mass component using data from the LIGO and Virgo observatories through the completion of their third observing run. The observation of a merger with a component below $1\,M_{\odot}$ would be a clear sign of either new physics or the existence of a primordial black hole population; these black holes could also contribute to the dark matter distribution. Our search targets binaries where the primary has mass $M_1$ between 0.1-100$\,M_{\odot}$ and the secondary has mass $M_2$ from 0.1-1$\,M_{\odot}$ for $M_1 < 20\,M_\odot$ and 0.01-1$\,M_{\odot}$ for $M_1 \ge 20\,M_\odot$. Sources with $M_1 < 7\,M_\odot, M_2 > 0.5\,M_\odot$ are also allowed to have orbital eccentricity up to $e_{10} \sim 0.3$. This search region covers from comparable to extreme mass ratio sources up to $10^4:1$. We find no statistically convincing candidates and so place new upper limits on the rate of mergers; our analysis sets the first limits for most subsolar sources with $7\,M_{\odot}< M_1 < 20\,M_{\odot}$ and tightens limits by $\sim 8\times$ $(1.6\times)$ where $M_1 > 20\,M_{\odot}$ ($M_1 < 7\,M_{\odot}$). Using these limits, we constrain the dark matter fraction to below 0.3 (0.7)$\%$ for 1 (0.5)$\,M_{\odot}$ black holes assuming a monochromatic mass function. Due to the high merger rate of primordial black holes beyond the individual source horizon distance, we also use the lack of an observed stochastic background as a complementary probe to limit the dark matter fraction. We find that although the limits are in general weaker than those from the direct search they become comparable at $0.1 \,M_{\odot}$.

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Stochastic Gravitational Wave Background from PBH-ABH Mergers

Published Paper #: 1001

Authors:, Wenfeng Cui, Fei Huang, Jing Shu, Yue Zhao,

Journal: Chinese Physics C, Vol. 46, No. 5 (2022)

url: http://arxiv.org/pdf/2108.04279v2.pdf

Abstract: The measurement of gravitational waves produced by binary black-hole mergers at the Advanced LIGO has encouraged extensive studies on the stochastic gravitational wave background. Recent studies have focused on gravitational wave sources made of the same species, such as mergers from binary primordial black holes or those from binary astrophysical black holes. In this paper, we study a new possibility -- the stochastic gravitational wave background produced by mergers of one primordial black hole and one astrophysical black hole. Such systems are necessarily present if primordial black holes exist. We study the isotropic gravitational wave background produced through the history of the Universe. We find it is very challenging to detect such a signal. We also demonstrate that it is improper to treat the gravitational waves produced by such binaries in the Milky Way as a directional stochastic background, due to a very low binary formation rate.

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Erratum: Primordial black hole origin for thermal gamma-ray bursts

Published Paper #: 1000

Authors:, Oscar del Barco,

Journal: Monthly Notices of the Royal Astronomical Society 512, 2925-2928
 (2022)

url: http://arxiv.org/pdf/2007.11226v4.pdf

Abstract: This Erratum modifies the original article entitled "Primordial black hole origin for thermal gamma ray bursts", which was published in Monthly Notices of the Royal Astronomical Society 506, 806 (2021).

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Inflation with $0 \leq c_{\rm s} \leq 1$

Published Paper #: 999

Authors:, Mohammad Ali Gorji, Hayato Motohashi, Shinji Mukohyama,

Journal: JCAP 02 (2022) 030

url: http://arxiv.org/pdf/2110.10731v2.pdf

Abstract: We investigate a novel single field inflationary scenario which allows a transition between a slow-roll k-inflation with $c_{\rm s}$ of order unity and a ghost inflation with $ c_{\rm s} \simeq 0$, where $ c_{\rm s}$ is the sound speed for the curvature perturbations. We unify the two phases smoothly by appropriately taking into account a higher derivative scordatura term, which is always there from the effective field theory point of view but which becomes important only in the $c_{\rm s} \simeq 0$ regime. The model achieves the whole range of $0 \leq c_{\rm s} \leq 1$ avoiding strong coupling and gradient instability, and allows us to access the $c_{\rm s} \simeq 0$ regime in a self-consistent manner. We also discuss implications to the formation of primordial black holes.

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A peek outside our Universe

Published Paper #: 998

Authors:, Enrique Gaztanaga, Pablo Fosalba,

Journal: Symmetry 2022, 14, 285

url: http://arxiv.org/pdf/2104.00521v2.pdf

Abstract: According to general relativity (GR), a universe with a cosmological constant $\Lambda$, like ours, is trapped inside an event horizon, $r< \sqrt{3/\Lambda}$. What is outside? We show, using Israel (1967) junction conditions, that there could be a different universe outside. Our universe looks like a black hole for an outside observer. Outgoing radial null geodesics cannot escape our universe, but incoming photons can enter and leave an imprint on our CMB sky. We present a picture of such a fossil record from the analysis of CMB maps that agrees with the black hole universe predictions but challenges our understanding of the origin of the primordial universe.

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Non-Gaussianity in inflationary scenarios for primordial black holes

Published Paper #: 997

Authors:, Matthew W. Davies, Pedro Carrilho, David J. Mulryne,

Journal: JCAP06(2022)019

url: http://arxiv.org/pdf/2110.08189v2.pdf

Abstract: Working in an idealised framework in which a series of phases of evolution defined by the second slow-roll parameter $\eta$ are matched together, we calculate the reduced bispectrum, $f_{\rm NL}$, for models of inflation with a large peak in their primordial power spectra. We find $f_{\rm NL}$ is typically approximately constant over scales at which the peak is located, and provide an analytic approximation for this value. This allows us to identify the conditions under which $f_{\rm NL}$ is large enough to have a significant impact on the resulting production of primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). Together with analytic formulae for the gradient of the rise and fall in the power spectrum, this provides a toolkit for designing or quickly analysing inflationary models that produce PBHs and SIGWs.

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Primordial black holes in nonminimal derivative coupling inflation with   quartic potential and reheating consideration

Published Paper #: 996

Authors:, Soma Heydari, Kayoomars Karami,

Journal: Eur. Phys. J. C 82, 83 (2022)

url: http://arxiv.org/pdf/2107.10550v2.pdf

Abstract: We investigate the generation of Primordial Black Holes (PBHs) with the aid of gravitationally increased friction mechanism originated from the NonMinimal field Derivative Coupling (NMDC) to gravity framework, with the quartic potential. Applying the coupling parameter as a two-parted function of inflaton field and fine-tuning of five parameter assortments we can acquire ultra slow-roll phase to slow down the inflaton field due to high friction. This enables us to achieve enough enhancement in the amplitude of curvature perturbations power spectra to generate PBHs with different masses. The reheating stage is considered to obtain criteria for PBHs generation during radiation dominated era. We demonstrate that three cases of asteroid mass PBHs ($10^{-12}M_{\odot}$, $10^{-13}M_{\odot}$, and $10^{-15}M_{\odot})$ can be very interesting candidates for comprising $100\%$ , $98.3\%$ and $99.1\%$ of the total Dark Matter (DM) content of the universe. Moreover, we analyse the production of induced Gravitational Waves (GWs), and illustrate that their spectra of current density parameter $(\Omega_{\rm GW_0})$ for all parameter Cases foretold by our model have climaxes which cut the sensitivity curves of GWs detectors, ergo the veracity of our outcomes can be tested in light of these detectors. At last, our numerical results exhibit that the spectra of $\Omega_{\rm GW_0}$ behave as a power-law function with respect to frequency, $\Omega_{\rm GW_0} (f) \sim (f/f_c)^{n} $, in the vicinity of climaxes. Also, in the infrared regime $f\ll f_{c}$, the power index satisfies the relation $n=3-2/\ln(f_c/f)$.

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Primordial black holes and lepton flavor violation with scotogenic dark   matter

Published Paper #: 995

Authors:, Teruyuki Kitabayashi,

Journal: Prog Theor Exp Phys (2022)

url: http://arxiv.org/pdf/2107.11692v4.pdf

Abstract: We show that if the lepton flavor violating $\mu \rightarrow e \gamma$ process is observed in the MEG II experiment, the initial density of primordial black holes (PBHs) can be constrained with the scotogenic dark matter. As a benchmark case, if the PBH evaporation occurs in the radiation dominated era, the initial density may be $2\times 10^{-17} \lesssim \beta \lesssim 3 \times 10^{-16}$ for $\mathcal{O}$ (TeV) scale dark sector in the scotogenic model where $\beta=\rho_{\rm PBH}/\rho_{\rm rad}$ is the ratio of the PBH density $\rho_{\rm PBH}$ to the radiation density $\rho_{\rm rad}$ at the time of PBH formation. As an other benchmark case, if PBHs evaporate in the PBH dominated era, the initial density may be $1 \times 10^{-8} \lesssim \beta \lesssim 3 \times 10^{-7}$ for $\mathcal{O}$ (GeV) scale dark matter with other $\mathcal{O}$ (TeV) scale particles in the scotogenic model.

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Primordial Black Hole Evaporation and Dark Matter Production: II.   Interplay with the Freeze-In/Out Mechanism

Published Paper #: 994

Authors:, Andrew Cheek, Lucien Heurtier, Yuber F. Perez-Gonzalez, Jessica Turner,

Journal: Phys. Rev. D 105 (2022) 015023

url: http://arxiv.org/pdf/2107.00016v2.pdf

Abstract: We study how the evaporation of primordial black holes (PBHs) can affect the production of dark matter (DM) particles through thermal processes. We consider fermionic DM interacting with Standard Model particles via a spin-1 mediator in the context of a Freeze-Out or Freeze-In mechanism. We show that when PBHs evaporate after dominating the Universe's energy density, PBHs act as a source of DM and continuously inject entropy into the visible sector that can affect the thermal production in three qualitatively different ways. We compute the annihilation cross-sections which account for the interactions between and within the PBH produced and thermally produced DM populations, and establish a set of Boltzmann equations which we solve to obtain the correct relic abundance in those different regimes and confront the results with a set of different cosmological constraints. We provide analytic formulae to calculate the relic abundance for the Freeze-Out and Freeze-In mechanism in a PBH dominated early Universe. We identify regions of the parameter space where the PBHs dilute the relic density and thermalization occurs. Furthermore, we have made our code that numerically solves the Boltzmann equations publicly available.

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Primordial Black Hole Evaporation and Dark Matter Production: I. Solely   Hawking radiation

Published Paper #: 993

Authors:, Andrew Cheek, Lucien Heurtier, Yuber F. Perez-Gonzalez, Jessica Turner,

Journal: Phys. Rev. D 105 (2022) 015022

url: http://arxiv.org/pdf/2107.00013v2.pdf

Abstract: Hawking evaporation of black holes in the early Universe is expected to copiously produce all kinds of particles, regardless of their charges under the Standard Model gauge group. For this reason, any fundamental particle, known or otherwise, could be produced during the black hole lifetime. This certainly includes dark matter (DM) particles. This paper improves upon previous calculations of DM production from primordial black holes (PBH) by consistently including the greybody factors, and by meticulously tracking a system of coupled Boltzmann equations. We show that the initial PBH densities required to produce the observed relic abundance depend strongly on the DM spin, varying in about $\sim 2$ orders of magnitude between a spin-2 and a scalar DM in the case of non-rotating PBHs. For Kerr PBHs, we have found that the expected enhancement in the production of bosons reduces the initial fraction needed to explain the measurements. We further consider indirect production of DM by assuming the existence of additional and unstable degrees of freedom emitted by the evaporation, which later decay into the DM. For a minimal setup where there is only one heavy particle, we find that the final relic abundance can be increased by at most a factor of $\sim 4$ for a scalar heavy state and a Schwarzschild PBH, or by a factor of $\sim 4.3$ for a spin-2 particle in the case of a Kerr PBH.

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PBH formation from spherically symmetric hydrodynamical perturbations: a   review

Published Paper #: 992

Authors:, Albert Escrivà,

Journal: Universe 2022, 8(2), 66

url: http://arxiv.org/pdf/2111.12693v3.pdf

Abstract: Primordial black holes, which could have been formed in the very early Universe due to the collapse of large curvature fluctuations, are nowadays one of the most attractive and fascinating research areas in cosmology for their possible theoretical and observational implications. This review article presents the current results and developments on the conditions for primordial black hole formation from the collapse of curvature fluctuations in spherical symmetry on a Friedman-Lemaitre-Robertson-Walker background and its numerical simulation. We review the appropriate formalism for the conditions of primordial black hole formation, and we detail a numerical implementation. We then focus on different results regarding the threshold and the black hole mass using different sets of curvature fluctuations. Finally, we present the current state of analytical estimations for the primordial black hole formation threshold, contrasted with numerical simulations.

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NANOGrav Hints on Planet-Mass Primordial Black Holes

Published Paper #: 991

Authors:, Guillem Domènech, Shi Pi,

Journal: SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 65, Issue 3:
 230411(2022)

url: http://arxiv.org/pdf/2010.03976v3.pdf

Abstract: Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array (PTA) time residuals from their 12.5 year data, which might be the first detection of the stochastic background of gravitational waves (GWs). We show that the amplitude and the power index of such waves imply that they could be the secondary GWs induced by the peaked curvature perturbation with a dust-like post inflationary era with $-0.091\lesssim w\lesssim0.048$. Such stochastic background of GWs naturally predicts substantial existence of planet-mass primordial black holes (PBHs), which can be the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment (OGLE).

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Background of radio photons from primordial black holes

Published Paper #: 990

Authors:, Shikhar Mittal, Girish Kulkarni,

Journal: MNRAS 510 (2022) 4992

url: http://arxiv.org/pdf/2110.11975v3.pdf

Abstract: We compute the isotropic radiation background due to Hawking emission from primordial black holes (PBHs), and examine if this background is a viable option in explaining the excess radiowave background observed by the ARCADE2 and LWA1 experiments at $\lesssim 1\,$GHz. We find that even under the extreme assumption that all of the dark matter is in the form of PBHs, the radio brightness temperature induced by Hawking evaporation of PBHs is $\mathcal{O}(10^{-46})\,$K, highly subdominant compared to the cosmic microwave background. The main reason for this is that for PBHs in the mass range $\sim10^{12}$-$10^{14}\,$kg, which can be constrained by Hawking emission, the spectrum peaks at $10^7$ to $10^5\,$eV. As the Hawking spectrum is power law suppressed towards lower energies, negligible flux of $\mu$eV photons is obtained. The peak of the Hawking spectrum shifts to lower energies for higher masses, but the number density is low and so is the specific intensity. Because Hawking emission from PBHs is thus unable to explain the observed excess radio background, we also consider the alternative possibility of radio emission from gas accretion onto supermassive PBHs. These PBHs can readily produce strong radio emission that could easily explain the ARCADE2/LWA1 excess.

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Predictions for local PNG bias in the galaxy power spectrum and   bispectrum and the consequences for $f_{\rm NL}$ constraints

Published Paper #: 989

Authors:, Alexandre Barreira,

Journal: JCAP01(2022)033

url: http://arxiv.org/pdf/2107.06887v3.pdf

Abstract: We use hydrodynamical separate universe simulations with the IllustrisTNG model to predict the local primordial non-Gaussianity (PNG) bias parameters $b_{\phi}$ and $b_{\phi\delta}$, which enter at leading order in the galaxy power spectrum and bispectrum. This is the first time that $b_{\phi\delta}$ is measured from either gravity-only or galaxy formation simulations. For dark matter halos, the popular assumption of universality overpredicts the $b_{\phi\delta}(b_1)$ relation in the range $1 \lesssim b_1 \lesssim 3$ by up to $\Delta b_{\phi\delta} \sim 3$ ($b_1$ is the linear density bias). The adequacy of the universality relation is worse for the simulated galaxies, with the relations $b_{\phi}(b_1)$ and $b_{\phi\delta}(b_1)$ being generically redshift-dependent and very sensitive to how galaxies are selected (we test total, stellar and black hole mass, black hole mass accretion rate and color). The uncertainties on $b_{\phi}$ and $b_{\phi\delta}$ have a direct, often overlooked impact on the constraints of the local PNG parameter $f_{\rm NL}$, which we study and discuss. For a survey with $V = 100{\rm Gpc}^3/h^3$ at $z=1$, uncertainties $\Delta b_{\phi} \lesssim 1$ and $\Delta b_{\phi\delta} \lesssim 5$ around values close to the fiducial can yield relatively unbiased constraints on $f_{\rm NL}$ using power spectrum and bispectrum data. We also show why priors on galaxy bias are useful even in analyses that fit for products $f_{\rm NL} b_{\phi}$ and $f_{\rm NL} b_{\phi\delta}$. The strategies we discuss to deal with galaxy bias uncertainties can be straightforwardly implemented in existing $f_{\rm NL}$ constraint analyses (we provide fits for some of the bias relations). Our results motivate more works with galaxy formation simulations to refine our understanding of $b_{\phi}$ and $b_{\phi\delta}$ towards improved constraints on $f_{\rm NL}$.

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Dynamics and merger rate of primordial black holes in a cluster

Published Paper #: 988

Authors:, Viktor D. Stasenko, Alexander A. Kirillov, Konstantin M. Belotsky,

Journal: Universe 2022, 8(1), 41

url: http://arxiv.org/pdf/2111.13451v2.pdf

Abstract: The PBHs clusters can be source of gravitational waves, and the merger rate depends on the spatial distribution of PBHs in the cluster which changes over time. It is well known that gravitational collisional systems experience the core collapse, that leads to significantly increase of the central density and shrinking of the core. After core collapse, the cluster expands almost self-similarly (i.e. density profile extends in size without changing its shape). These dynamic processes affect at the merger rate of PBHs. In this paper the dynamics of the PBH cluster is considered using the Fokker-Planck equation. We calculate the merger rate of PBHs on cosmic time scales and show that its time dependence has a unique signature. Namely, it grows by about an order of magnitude at the moment of core collapse which depends on the characteristic of the cluster, and then decreases according to the dependence $\mathcal{R} \propto t^{-1.48}$. It was obtained for monochromatic and power-law PBH mass distributions with some fixed parameters. Obtained results can be used to test the model of the PBH clusters via observation of gravitational waves at high redshift.

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Constraining spinning primordial black holes with global 21-cm signal

Published Paper #: 987

Authors:, Pravin Kumar Natwariya, Alekha C. Nayak, Tripurari Srivastava,

Journal: Mon. Not. R. Astron. Soc. 510, 4236 (2021)

url: http://arxiv.org/pdf/2107.12358v2.pdf

Abstract: We study the upper projected bounds on the dark matter fraction in the form of the primordial black holes (PBHs) with a non-zero spin by using the absorption feature in the global 21-cm signal at redshift z ~ 17. The mass and spin are fundamental properties of a black hole, and they can substantially affect the evaporation rate of the black hole. The evaporating black hole can inject energy into the intergalactic medium and heat the gas. Subsequently, it can modify the absorption amplitude in the global 21-cm signal. Therefore, the absorption feature in the 21-cm signal can provide a robust bound on PBHs. We analyse the projected constraints on the dark matter fraction in the form of both spinning and non-spinning PBHs. The constraints are more stringent for spinning PBHs than non-spinning ones. We also compare these bounds with other observations and find the most stringent lower constraint on PBHs mass, which is allowed to constitute the entire dark matter to 6.7 x 10^17 g for extremal spinning PBHs.

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Primordial black hole production during first-order phase transitions

Published Paper #: 986

Authors:, Jing Liu, Ligong Bian, Rong-Gen Cai, Zong-Kuan Guo, Shao-Jiang Wang,

Journal: Phys.Rev.D 105 (2022) 2, L021303

url: http://arxiv.org/pdf/2106.05637v3.pdf

Abstract: Primordial black holes (PBHs) produced in the early Universe have attracted wide interest for their ability to constitute dark matter and explain the compact binary coalescence. We propose a new mechanism of PBH production during first-order phase transitions (PTs) and find that PBHs are naturally produced during PTs model-independently. Because of the randomness of the quantum tunneling, there always exists some probability that the vacuum decay is postponed in a whole Hubble volume. Since the vacuum energy density remains constant while radiation is quickly redshifted in the expanding Universe, the postponed vacuum decay then results in overdense regions, which finally collapse into PBHs as indicated by numerical simulations. Utilizing this result one can obtain mutual predictions and constraints between PBHs and GWs from PTs. The predicted mass function of PBHs is nearly monochromatic. We investigate two typical cases and find that 1) PBHs from a PT constitute all dark matter and GWs peak at $1$Hz, 2) PBHs from a PT can explain the coalescence events observed by LIGO-Virgo collaboration, and meanwhile GWs can explain the common-spectrum process detected by NANOGrav collaboration.

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Can Primordial Black Holes as all Dark Matter explain Fast Radio Bursts?

Published Paper #: 985

Authors:, Kimmo Kainulainen, Sami Nurmi, Enrico D. Schiappacasse, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 104, 123033 (2021)

url: http://arxiv.org/pdf/2108.08717v2.pdf

Abstract: Primordial black holes (PBHs) are one of the most interesting nonparticle dark matter (DM) candidates. They may explain all the DM content in the Universe in the mass regime from about $10^{-14}M_{\odot}$ to $10^{-11}M_{\odot}$. We study PBHs as the source of fast radio bursts (FRBs) via magnetic reconnection in the event of collisions between them and neutron stars (NSs) in galaxies. We investigate the energy loss of PBHs during PBH-NS encounters to model their capture by NSs. To an order-of-magnitude estimation, we conclude that the parameter space of PBHs being all DM is accidentally consistent with that to produce FRBs with a rate which is the order of the observed FRB rate.

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Gravitational waves $\times$ HI intensity mapping: cosmological and   astrophysical applications

Published Paper #: 984

Authors:, Giulio Scelfo, Marta Spinelli, Alvise Raccanelli, Lumen Boco, Andrea Lapi, Matteo Viel,

Journal: JCAP01(2022)004

url: http://arxiv.org/pdf/2106.09786v2.pdf

Abstract: Two of the most rapidly growing observables in cosmology and astrophysics are gravitational waves (GW) and the neutral hydrogen (HI) distribution. In this work, we investigate the cross-correlation between resolved gravitational wave detections and HI signal from intensity mapping (IM) experiments. By using a tomographic approach with angular power spectra, including all projection effects, we explore possible applications of the combination of the Einstein Telescope and the SKAO intensity mapping surveys. We focus on three main topics: \textit{(i)} statistical inference of the observed redshift distribution of GWs; \textit{(ii)} constraints on dynamical dark energy models as an example of cosmological studies; \textit{(iii)} determination of the nature of the progenitors of merging binary black holes, distinguishing between primordial and astrophysical origin. Our results show that: \textit{(i)} the GW redshift distribution can be calibrated with good accuracy at low redshifts, without any assumptions on cosmology or astrophysics, potentially providing a way to probe astrophysical and cosmological models; \textit{(ii)} the constrains on the dynamical dark energy parameters are competitive with IM-only experiments, in a complementary way and potentially with less systematics; \textit{(iii)} it will be possible to detect a relatively small abundance of primordial black holes within the gravitational waves from resolved mergers. Our results extend towards $\mathrm{GW \times IM}$ the promising field of multi-tracing cosmology and astrophysics, which has the major advantage of allowing scientific investigations in ways that would not be possible by looking at single observables separately.

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Could the 2.6 $M_\odot$ object in GW190814 be a primordial black hole?

Published Paper #: 983

Authors:, Kyriakos Vattis, Isabelle S. Goldstein, Savvas M. Koushiappas,

Journal: Phys. Rev. D 102, 061301 (2020)

url: http://arxiv.org/pdf/2006.15675v3.pdf

Abstract: On June 20, 2020, the LIGO-Virgo collaboration announced the discovery of GW190814, a gravitational wave event originating from a binary system merger between a black hole of mass $M_1 = 23.2^{+1.1} _ {-1.0}M_\odot$ and an unidentified object with a mass of $M_2 = 2.59^{+0.08} _ {-0.09}M_\odot$. This second object would be either the heaviest neutron star or lightest black hole observed to date. Here we investigate the possibility of the $\sim 2.6M_\odot$ object being a primordial black hole (PBH). We find that a primordial black hole explanation to GW190814 is unlikely as it is limited by the formation rate of the primary stellar progenitor and the observed merger rates of $\mathcal{O}(20)M_\odot$ massive black hole pairs.

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Direct Detection of Light Dark Matter from Evaporating Primordial Black   Holes

Published Paper #: 982

Authors:, Roberta Calabrese, Marco Chianese, Damiano F. G. Fiorillo, Ninetta Saviano,

Journal: PRD 105, L021302, 2022

url: http://arxiv.org/pdf/2107.13001v2.pdf

Abstract: The direct detection of sub-GeV dark matter interacting with nucleons is hampered by the low recoil energies induced by scatterings in the detectors. This experimental difficulty is avoided in the scenario of boosted dark matter where a component of dark matter particles is endowed with large kinetic energies. In this Letter, we point out that the current evaporation of primordial black holes with masses from $10^{14}$ to $10^{16}$ g is a source of boosted light dark matter with energies of tens to hundreds of MeV. Focusing on the XENON1T experiment, we show that these relativistic dark matter particles could give rise to a signal orders of magnitude larger than the present upper bounds. Therefore, we are able to significantly constrain the combined parameter space of primordial black holes and sub-GeV dark matter. In the presence of primordial black holes with a mass of $10^{15}~\mathrm{g}$ and an abundance compatible with present bounds, the limits on DM-nucleon cross-section are improved by four orders of magnitude.

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GW200105 and GW200115 are compatible with a scenario of primordial black   hole binary coalescences

Published Paper #: 981

Authors:, Sai Wang, Zhi-Chao Zhao,

Journal: Eur. Phys. J. C 82, 9 (2022)

url: http://arxiv.org/pdf/2107.00450v2.pdf

Abstract: Two gravitational wave events, i.e. GW200105 and GW200115, were observed by the Advanced LIGO and Virgo detectors recently. In this work, we show that they can be explained by a scenario of primordial black hole binaries that are formed in the early Universe. The merger rate predicted by such a scenario could be consistent with the one estimated from LIGO and Virgo, even if primordial black holes constitute a fraction of cold dark matter. The required abundance of primordial black holes is compatible with the existing upper limits from microlensing, caustic crossing and cosmic microwave background observations.

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Prospective Sensitivities of Atom Interferometers to Gravitational Waves   and Ultralight Dark Matter

Published Paper #: 980

Authors:, Leonardo Badurina, Oliver Buchmueller, John Ellis, Marek Lewicki, Christopher McCabe, Ville Vaskonen,

Journal: Phil. Trans. R. Soc. A.380 20210060, 2022

url: http://arxiv.org/pdf/2108.02468v2.pdf

Abstract: We survey the prospective sensitivities of terrestrial and space-borne atom interferometers (AIs) to gravitational waves (GWs) generated by cosmological and astrophysical sources, and to ultralight dark matter. We discuss the backgrounds from gravitational gradient noise (GGN) in terrestrial detectors, and also binary pulsar and asteroid backgrounds in space-borne detectors. We compare the sensitivities of LIGO and LISA with those of the 100m and 1km stages of the AION terrestrial AI project, as well as two options for the proposed AEDGE AI space mission with cold atom clouds either inside or outside the spacecraft, considering as possible sources the mergers of black holes and neutron stars, supernovae, phase transitions in the early Universe, cosmic strings and quantum fluctuations in the early Universe that could have generated primordial black holes. We also review the capabilities of AION and AEDGE for detecting coherent waves of ultralight scalar dark matter.

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Evaporating Primordial Black Holes in Gamma Ray and Neutrino Telescopes

Published Paper #: 979

Authors:, Antonio Capanema, AmirFarzan Esmaeili, Arman Esmaili,

Journal: JCAP12(2021)051

url: http://arxiv.org/pdf/2110.05637v3.pdf

Abstract: A primordial black hole in the last stages of evaporation and located in the local neighborhood can produce a detectable signal in gamma ray and neutrino telescopes. We re-evaluate the expected gamma ray and neutrino fluxes from these transient point events and discuss the consequences for existing constraints. For gamma rays we improve the current bounds by a factor of few, while for neutrinos we obtain significantly different results than the existing literature. The capability and advantages of neutrino telescopes in the search for primordial black holes is discussed thoroughly. The correlations of gamma ray and neutrino energy and time profiles will be promoted as a powerful tool in identifying the primordial black holes, in case of detection.

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Spin of primordial black holes in the model with collapsing domain walls

Published Paper #: 978

Authors:, Yury N. Eroshenko,

Journal: JCAP 12, 041 (2021)

url: http://arxiv.org/pdf/2111.03403v2.pdf

Abstract: The angular momentum (spin) acquisition by a collapsing domain wall at the cosmological radiation-dominated stage is investigated. During the collapses, primordial black holes and their clusters can be born in various mass ranges. Spin accumulation occurs under the influence of tidal gravitational perturbations from the surrounding density inhomogeneities at the epoch when the domain wall crosses the cosmological horizon. It is shown that the dimensionless spin parameter can have the small values $a_S<1$ only for primordial black holes with masses $M>10^{-3}M_\odot$, whereas less massive black holes receive extreme spins $a_S\simeq1$. It is possible that primordial black holes obtain an additional spin due to the vector mode of perturbations.

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Type Ia Supernova Magnitude Step from the local Dark Matter Environment

Published Paper #: 977

Authors:, Heinrich Steigerwald, Davi Rodrigues, Stefano Profumo, Valerio Marra,

Journal: MNRAS 510 (4), 4779-4795 (2022)

url: http://arxiv.org/pdf/2112.09739v1.pdf

Abstract: Residuals in the Hubble diagram at optical wavelengths and host galaxy stellar mass are observed to correlate in Type Ia supernovae (SNe Ia) (`magnitude step'). Among possible progenitor channels for the associated explosions, those based on dark matter (DM) have attracted significant attention, including our recent proposal that `normal' SNe Ia from bare detonations in sub-Chandrasekhar white dwarf stars are triggered by the passage of asteroid-mass primordial black holes (PBHs): the magnitude step could then originate from a brightness dependence on stellar properties, on DM properties, or both. Here, we present a method to estimate the local DM density and velocity dispersion of the environment of SN Ia progenitors. We find a luminosity step of $0.52\pm 0.11\,$mag corresponding to bins of high vs low DM density in a sample of 222 low-redshift events from the Open Supernova Catalog. We investigate whether the magnitude step can be attributed to local DM properties alone, assuming asteroid-mass PBHs. Given the inverse correlation between SN Ia brightness and PBH mass, an intriguing explanation is a spatially-inhomogeneous PBH mass function. If so, a strong mass segregation in the DM density-dependent PBH mass scale is needed to explain the magnitude step. While mass segregation is observed in dense clusters, it is unlikely to be realized on galactic scales. Therefore, if DM consists of asteroid-mass PBHs, the magnitude step is more likely to exist, and dominantly to be attributed to local stellar properties.

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Search for black hole hyperbolic encounters with gravitational wave   detectors

Published Paper #: 976

Authors:, Gonzalo Morrás, Juan García-Bellido, Savvas Nesseris,

Journal: Physics of the Dark Universe 35 (2022) 100932

url: http://arxiv.org/pdf/2110.08000v2.pdf

Abstract: In recent years, the proposal that there is a large population of primordial black holes living in dense clusters has been gaining popularity. One natural consequence of these dense clusters will be that the black holes inside will gravitationally scatter off each other in hyperbolic encounters, emitting gravitational waves that can be observed by current detectors. In this paper we will derive how to compute the gravitational waves emitted by black holes in hyperbolic orbits, taking into account up to leading order spin effects. We will then study the signal these waves leave in the network of gravitational wave detectors currently on Earth. Using the properties of the signal, we will detail the data processing techniques that can be used to make it stand above the detector noise. Finally, we will look for these signals from hyperbolic encounters in the publicly available LIGO-Virgo data. For this purpose we will develop a two step trigger. The first step of the trigger will be based on looking for correlations between detectors in the time-frequency domain. The second step of the trigger will make use of a residual convolutional neural network, trained with the theoretical predictions for the signal, to look for hyperbolic encounters. With this trigger we find 8 hyperbolic encounter candidates in the 15.3 days of public data analyzed. Some of these candidates are promising, but the total number of candidates found is consistent with the number of false alarms expected from our trigger.

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Primordial Black Hole Generation in a Two-field Inflationary Model

Published Paper #: 975

Authors:, Lilia Anguelova,

Journal: Springer Proc. Math. Stat. 396 (2022) 193-202

url: http://arxiv.org/pdf/2112.07614v1.pdf

Abstract: We summarize our work on the generation of primordial black holes in a type of two-field inflationary models. The key ingredient is a sharp turn of the background trajectory in field space. We show that certain classes of solutions to the equations of motion exhibit precisely this kind of behavior. Among them we find solutions, which describe a transition between an ultra-slow roll and a slow roll phases of inflation.

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Solar Mass Primordial Black Holes in Moduli Dominated Universe

Published Paper #: 974

Authors:, Sukannya Bhattacharya, Anirban Das, Koushik Dutta,

Journal: JCAP 10 (2021) 071

url: http://arxiv.org/pdf/2101.02234v2.pdf

Abstract: We explore the prospect of producing primordial black holes around the solar mass region during an early matter domination epoch. The early matter-dominated epoch can arise when a moduli field comes to dominate the energy density of the Universe prior to big bang nucleosynthesis. The absence of radiation pressure during a matter-dominated epoch enhances primordial black hole formation from the gravitational collapse of primordial density fluctuations. In particular, we find that primordial black holes are produced in the $0.1-10~M_{\odot}$ mass range with a favorable choice of parameters in the theory. However, they cannot explain all of the merger events detected by the LIGO/Virgo gravitational wave search. In such a case, primordial black holes form about $4\%$ of the total dark matter abundance, of which $95\%$ belongs to the LIGO/Virgo consistent mass range. The rest of the dark matter could be in the form of particles that are produced from the decay of the moduli field during reheating.

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Probing ultralight dark matter with future ground-based   gravitational-wave detectors

Published Paper #: 973

Authors:, Chen Yuan, Richard Brito, Vitor Cardoso,

Journal: Phys. Rev. D 104, 044011 (2021)

url: http://arxiv.org/pdf/2106.00021v2.pdf

Abstract: Ultralight bosons are possible fundamental building blocks of nature, and promising dark matter candidates. They can trigger superradiant instabilities of spinning black holes (BHs) and form long-lived "bosonic clouds" that slowly dissipate energy through the emission of gravitational waves (GWs). Previous studies constrained ultralight bosons by searching for the stochastic gravitational wave background (SGWB) emitted by these sources in LIGO data, focusing on the most unstable dipolar and quadrupolar modes. Here we focus on scalar bosons and extend previous works by: (i) studying in detail the impact of higher modes in the SGWB; (ii) exploring the potential of future proposed ground-based GW detectors, such as the Neutron Star Extreme Matter Observatory, the Einstein Telescope and Cosmic Explorer, to detect this SGWB. We find that higher modes largely dominate the SGWB for bosons with masses $\gtrsim 10^{-12}$ eV, which is particularly relevant for future GW detectors. By estimating the signal-to-noise ratio of this SGWB, due to both stellar-origin BHs and from a hypothetical population of primordial BHs, we find that future ground-based GW detectors could observe or constrain bosons in the mass range $\sim [7\times 10^{-14}, 2\times 10^{-11}]$ eV and significantly improve on current and future constraints imposed by LIGO and Virgo observations.

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Primordial black holes and secondary gravitational waves from string   inspired general no-scale supergravity

Published Paper #: 972

Authors:, Lina Wu, Yungui Gong, Tianjun Li,

Journal: Phys. Rev. D 104 (2021), 123544

url: http://arxiv.org/pdf/2105.07694v2.pdf

Abstract: The formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) have been studied in the generic no-scale supergravity inflationary models. By adding an exponential term to the K\"ahler potential, the inflaton experiences a period of ultraslow-roll and the amplitude of primordial power spectrum at small scales is enhanced to $\mathcal{O}(10^{-2})$. The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. A wide mass range of PBHs can be produced in our model, and the frequencies of the accompanied SIGWs are ranged form nanohertz to kilohertz. We show four benchmark points where the generated PBH masses are around $\mathcal{O}(10^{-16}M_{\odot})$, $\mathcal{O}(10^{-12}M_{\odot})$, $\mathcal{O}(10^{-2}M_{\odot})$ and $\mathcal{O}(10^{2}M_{\odot})$. The PBHs with masses around $\mathcal{O}(10^{-16}M_{\odot})$ and $ \mathcal{O}(10^{-12}M_{\odot})$ can make up almost all the dark matter, and the accompanied SIGWs can be probed by the upcoming space-based gravitational wave observatory. Also, the SIGWs accompanied with the formation of stellar mass PBHs can be used to interpret the stochastic GW background in the nanohertz band, detected by the North American Nanohertz Observatory for gravitational waves, and can be tested by future interferometric gravitational wave observatory.

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Angular correlation as a novel probe of supermassive primordial black   holes

Published Paper #: 971

Authors:, Takumi Shinohara, Teruaki Suyama, Tomo Takahashi,

Journal: Phys. Rev. D 104, 023526 (2021)

url: http://arxiv.org/pdf/2103.13692v3.pdf

Abstract: We investigate the clustering property of primordial black holes (PBHs) in a scenario where PBHs can explain the existence of supermassive black holes (SMBHs) at high redshifts. We analyze the angular correlation function of PBHs originating from fluctuations of a spectator field which can be regarded as a representative model to explain SMBHs without conflicting with the constraint from the spectral distortion of cosmic microwave background. We argue that the clustering property of PBHs can give a critical test for models with PBHs as the origin of SMBHs and indeed show that the spatial distribution of PBHs in such a scenario is highly clustered, which suggests that those models may be disfavored from observations of SMBHs although a careful comparison with observational data would be necessary.

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Primordial Black Holes from Confinement

Published Paper #: 970

Authors:, Gia Dvali, Florian Kuhnel, Michael Zantedeschi,

Journal: Phys. Rev. D 104 (2021) 123507

url: http://arxiv.org/pdf/2108.09471v2.pdf

Abstract: A mechanism for the formation of primordial black holes is proposed. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry. The large amount of energy stored in the colour flux tubes connecting the quark pair leads to black-hole formation. These are much lighter and can be of higher spin than those produced by standard collapse of horizon-size inflationary overdensities. Other difficulties exhibited by such mechanisms are also avoided. Phenomenological features of the new mechanism are discussed as well as accounting for both the entirety of the dark matter and the supermassive black holes in the galactic centres. Under proper conditions, the mechanism can be realised in a generic confinement theory, including ordinary QCD. We discuss a possible string-theoretic realisation via $D$-branes. Interestingly, for conservative values of the string scale, the produced gravity waves are within the range of recent NANOGrav data. Simple generalisations of the mechanism allow for the existence of a significant scalar component of gravity waves with distinct observational signatures.

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Torsion in string-inspired cosmologies and the universe dark sector

Published Paper #: 969

Authors:, Nick E. Mavromatos,

Journal: Universe 7 (2021) 12, 480

url: http://arxiv.org/pdf/2111.05675v3.pdf

Abstract: I review several aspects of torsion in string-inspired cosmologies. In particular, I discuss its connection with fundamental, string-model independent, axion fields associated with the massless gravitational multiplet of the string. I argue in favour of the role of primordial gravitational anomalies coupled to such axions in inducing inflation of a type encountered in the "running-vacuum-model (RVM)" cosmological framework, without fundamental inflaton fields. The gravitational-anomaly terms owe their existence to the Green-Schwarz mechanism for the (extra-dimensional) anomaly cancellation, and may be non-trivial in such theories in the presence of (primordial) gravitational waves at early stages of the four-dimensional string Universe (after compactification). I also discuss how the torsion-induced stringy axions can acquire a mass in the post inflationary era, due to non perturbative effects, thus having the potential to play the r\^ole of (a component of) dark matter in such models. Finally, I describe briefly the current-era phenomenology of this model, with the emphasis placed on the possibility of alleviating tensions observed in the current-era cosmological data. A brief phenomenological comparison with other cosmological models in contorted geometries is also made.

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Primordial Black Holes And Gravitational Waves Based On No-Scale   Supergravity

Published Paper #: 968

Authors:, Ioanna D. Stamou,

Journal: J.Phys.Conf.Ser. 2105 (2021) 8, 012008

url: http://arxiv.org/pdf/2111.14190v1.pdf

Abstract: In this paper we present a class of models in order to explain the production of Primordial Black Holes (PBHs) and Gravitational Waves (GWs) in the Universe. These models are based on no-scale theory. By breaking the SU(2,1)/SU(2)$\times$U(1) symmetry we fix one of the two chiral fields and we derive effective scalar potentials which are capable of generating PBHs and GWs. As it is known in the literature there is an important unification of the no-scale models, which leads to the Starobinsky effective scalar potential based on the coset SU(2,1)/SU(2)$\times$U(1). We use this unification in order to additionally explain the generation of PBHs and GWs. Concretely, we modify well-known superpotentials, which reduce to Starobinsky-like effective scalar potentials. Thus, we derive scalar potentials which, on the one hand, explain the production of PBHs and GWs and, on the other hand, they conserve the transformation laws, which yield from the parametrization of the coset SU(2,1)/SU(2)$\times$U(1) as well as the unification between the models which are yielded this coset. We numerically evaluate the scalar power spectra with the effective scalar potential based on this theory. Furthermore, we evaluate the fractional abundances of PBHs by comparing two methods the Press-Schechter approach and the peak theory, while focusing on explaining the dark matter in the Universe. By using the resulting scalar power spectrum we evaluate the amount of GWs. All models are in complete consistence with Planck constraints.

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Can QCD Axion Stars explain Subaru HSC microlensing?

Published Paper #: 967

Authors:, Enrico D. Schiappacasse, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 104, 103020 (2021)

url: http://arxiv.org/pdf/2109.13153v2.pdf

Abstract: A non-negligible fraction of the QCD axion dark matter may form gravitationally bound Bose Einstein condensates, which are commonly known as axion stars or axion clumps. Such astrophysical objects have been recently proposed as the cause for the single candidate event reported by Subaru Hyper Suprime-Cam (HSC) microlensing search in the Andromeda galaxy. Depending on the breaking scale of the Peccei-Quinn symmetry and the details of the dark matter scenario, QCD axion clumps may form via gravitational condensation during radiation domination, in the dense core of axion miniclusters, or within axion minihalos around primordial black holes. We analyze all these scenarios and conclude that the microlensing candidate detected by the Subaru HSC survey is likely not caused by QCD axion stars.

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Nucleosynthetic signatures of primordial origin around supermassive   black holes

Published Paper #: 966

Authors:, Phoebe Upton Sanderbeck, Simeon Bird, Zoltan Haiman,

Journal: Phys. Rev. D 104, 103022 (2021)

url: http://arxiv.org/pdf/2109.05035v2.pdf

Abstract: If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs) at the centers of high-redshift quasars, then the gas surrounding these black holes may reveal nucleosynthetic clues to their primordial origins. We present predictions of altered primordial abundances around PBHs massive enough to seed SMBHs at z~6-7.5. We find that if PBHs with initial masses of ~10^5 M$_{\odot}$ are responsible for such SMBHs, they may produce primordial Deuterium and Helium fractions enhanced by >~ 10%, and Lithium abundance depleted by >~10%, at distances of up to ~ a comoving kiloparsec away from the black hole after decoupling. We estimate that ~ 10^8 M$_{\odot}$ of gas is enhanced (or depleted) by at least one percent. Evidence of these modified primordial Deuterium, Helium, and Lithium abundances could still be present if this circum-PBH gas remains unaccreted by the SMBH and in or near the host galaxies of high-redshift quasars. Measuring the abundance anomalies will be challenging, but could offer a novel way to reveal the primordial origin of such SMBH seeds.

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Cherenkov Gravitational Radiation During the Radiation Era

Published Paper #: 965

Authors:, Yi-Zen Chu, Yen-Wei Liu,

Journal: Universe 2021, 7(11), 437

url: http://arxiv.org/pdf/2108.13463v2.pdf

Abstract: Cherenkov radiation may occur whenever the source is moving faster than the waves it generates. In a radiation dominated universe, with equation-of-state $w = 1/3$, we have recently shown that the Bardeen scalar-metric perturbations contribute to the linearized Weyl tensor in such a manner that its wavefront propagates at acoustic speed $\sqrt{w}=1/\sqrt{3}$. In this work, we explicitly compute the shape of the Bardeen Cherenkov cone and wedge generated respectively by a supersonic point mass (approximating a primordial black hole) and a straight Nambu-Goto wire (approximating a cosmic string) moving perpendicular to its length. When the black hole or cosmic string is moving at ultra-relativistic speeds, we also calculate explicitly the sudden surge of scalar-metric induced tidal forces on a pair of test particles due to the passing Cherenkov shock wave. These forces can stretch or compress, depending on the orientation of the masses relative to the shock front's normal.

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Impacts of Jets and Winds From Primordial Black Holes

Published Paper #: 964

Authors:, Volodymyr Takhistov, Philip Lu, Kohta Murase, Yoshiyuki Inoue, Graciela B. Gelmini,

Journal: Mon.Not.Roy.Astron.Soc. 517 (2022) L1

url: http://arxiv.org/pdf/2111.08699v1.pdf

Abstract: Primordial black holes (PBHs) formed in the early Universe constitute an attractive candidate for dark matter. Within the gaseous environment of the interstellar medium, PBHs with accretion disks naturally launch outflows such as winds and jets. PBHs with significant spin can sustain powerful relativistic jets and generate associated cocoons. Jets and winds can efficiently deposit their kinetic energies and heat the surrounding gas through shocks. Focusing on the Leo T dwarf galaxy, we demonstrate that these considerations can provide novel tests of PBHs over a significant $\sim 10^{-2} M_{\odot} - 10^6 M_{\odot}$ mass range, including the parameter space associated with gravitational wave observations by the LIGO and VIRGO Collaborations. Observing the morphology of emission could allow to distinguish between jet and wind contributions, and hence indirectly detect spinning PBHs.

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Lensing of gravitational waves as a probe of compact dark matter

Published Paper #: 963

Authors:, Juan Urrutia, Ville Vaskonen,

Journal: Mon. Not. Roy. Astron. Soc. 509 (2021) 1, 1358-1365

url: http://arxiv.org/pdf/2109.03213v3.pdf

Abstract: We study gravitational lensing of gravitational waves from compact object binaries as a probe of compact dark matter (DM) objects such as primordial black holes. Assuming a point mass lens, we perform parameter estimation of lensed gravitational wave signals from compact object binaries to determine the detectability of the lens with ground based laser interferometers. Then, considering binary populations that LIGO-Virgo has been probing, we derive a constraint on the abundance of compact DM from non-observation of lensed events. We find that the LIGO-Virgo observations imply that compact objects heavier than $M_l = 200M_\odot$ can not constitute all DM and less than $40\%$ of DM can be in compact objects heavier than $M_l = 400M_\odot$. We also show that the DM fraction in compact objects can be probed by LIGO in its final sensitivity for $M_l > 40M_\odot$ reaching $2\%$ of the DM abundance at $M_l > 200M_\odot$, and by ET for $M_l > 1M_\odot$ reaching DM fraction as low as $7\times 10^{-5}$ at $M_l > 40M_\odot$.

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Influences of accreting primordial black holes on the global 21 cm   signal in the dark ages

Published Paper #: 962

Authors:, Yupeng Yang,

Journal: MNRAS,508(2021)5709

url: http://arxiv.org/pdf/2110.06447v3.pdf

Abstract: Baryonic matter can be accreted on to primordial back holes (PBHs) formed in the early Universe. The radiation from accreting PBHs is capable of altering the evolution of the intergalactic medium (IGM), leaving marks on the global 21 cm signal in the dark ages. For accreting PBHs with mass $M_{\rm PBH}=10^{3}(10^{4})~M_{\odot}$ and mass fraction $f_{\rm PBH}=10^{-1}(10^{-3})$, the brightness temperature deviation $\Delta \delta T_{b}$ reaches $\sim 18~(26)~\rm mK$ at redshift $z\sim 90$ ($\nu \sim 16~\rm MHz$), and the gradient of the brightness temperature $d\delta T_{b}/d\nu$ reaches $ \sim 0.8~(0.5)~\rm mK~MHz^{-1}$ at frequency $\nu\sim 28~\rm MHz$ ($z\sim 50$). For larger PBHs with higher mass fraction, the brightness temperature deviation is larger in the redshift range $z\sim 30-300$ ($\nu\sim 5-46~\rm MHz$), and the gradient is lower at the frequency range $\nu \sim 20-60~\rm MHz$ ($z\sim 23-70$). It is impossible to detect these low frequency radio signals from the Earth due to the influence of the Earth's ionosphere. However, after taking care of the essential factors properly, e.g. the foreground and interference, future radio telescope in lunar orbit or on the farside surface of the Moon has a chance of detecting the global 21 cm signals impacted by accreting PBHs and distinguishing them from the standard model.

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Stellar Interferometry for Gravitational Waves

Published Paper #: 961

Authors:, I. H. Park, K. -Y. Choi, J. Hwang, S. Jung, D. H. Kim, M. H. Kim, C. -H. Lee, K. H. Lee, S. H. Oh, M. -G. Park, S. C. Park, A. Pozanenko, C. D. Rho, N. Vedenkin, E. Won,

Journal: Journal of Cosmology and Astroparticle Physics, 11, 008 (2021)

url: http://arxiv.org/pdf/1906.06018v4.pdf

Abstract: We propose a new method to detect gravitational waves, based on spatial coherence interferometry with stellar light, as opposed to the conventional temporal coherence interferometry with laser sources. The proposed method detects gravitational waves by using two coherent beams of light from a single distant star measured at separate space-based detectors with a long baseline. This method can be applied to either the amplitude or intensity interferometry. This experiment allows for the search of gravitational waves in the lower frequency range of $10^{-6}$ to $10^{-4}$ Hz. In this work, we present the detection sensitivity of the proposed stellar interferometer by taking the detector response and shot and acceleration noises into account. Furthermore, the proposed experimental setup is capable of searching for primordial black holes and studying the size of the target neutron star, which are also discussed in the paper.

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Exploring Evaporating Primordial Black Holes with Gravitational Waves

Published Paper #: 960

Authors:, Guillem Domènech, Volodymyr Takhistov, Misao Sasaki,

Journal: Phys.Lett.B 823 (2021) 136722

url: http://arxiv.org/pdf/2105.06816v2.pdf

Abstract: Primordial black holes (PBHs) from the early Universe have been connected with the nature of dark matter and can significantly affect cosmological history. We show that coincidence dark radiation and density fluctuation gravitational wave signatures associated with evaporation of $\lesssim10^9$ g PBHs can be used to explore and obtain important hints about the formation mechanisms of spinning and non-spinning PBHs spanning orders of magnitude in mass-range, which is challenging to do otherwise.

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Probing the effects of primordial black holes on 21-cm EDGES signal   along with interacting dark energy and dark matter - baryon scattering

Published Paper #: 959

Authors:, Ashadul Halder, Madhurima Pandey,

Journal: Mon. Not. Roy. Astron. Soc. 508, 3446 (2021)

url: http://arxiv.org/pdf/2101.05228v3.pdf

Abstract: 21-cm radio signal has emerged as an important probe in investigating the dark age of the Universe (recombination to reionization). In the current analysis, we explore the combined effects of primordial black holes (PBH), cooling off of the baryonic matter due to dark matter (DM) - baryon collisions and interaction of dark matter - dark energy (DE) fluid on the 21-cm brightness temperature. The variation of brightness temperature shows remarkable dependence on DM mass ($m_{\chi}$) and the dark matter - baryon scattering cross-section ($\sigma_0$). Bounds in $m_{\chi}$ - $\sigma_0$ parameter space are obtained for different possible PBH masses and for different interacting dark energy (IDE) models. These bounds are estimated based on the observed excess ($-500^{+200}_{-500}$ mK) of 21-cm brightness temperature by EDGES experiment. Eventually, bounds on PBH mass is also obtained for different values of dark matter mass and for different IDE model coupling parameters. The compatibility of the constraints of the IDE models, in the estimated bounds are also addressed.

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Brief Review of Recent Advances in Understanding Dark Matter and Dark   Energy

Published Paper #: 958

Authors:, Eugene Oks,

Journal: New Astronomy Reviews 2021, 93, 101632

url: http://arxiv.org/pdf/2111.00363v1.pdf

Abstract: Dark sector, constituting about 95 percent of the Universe, remains the subject of numerous studies. There are lots of models dealing with the cause of the effects assigned to dark matter and dark energy. This brief review is devoted to the very recent theoretical advances in these areas: only to the advances achieved in the last few years. For example, in section devoted to particle dark matter we overview recent publications on sterile neutrinos, self-interacting dark matter, dibarions, dark matter from primordial bubbles, primordial black holes as dark matter, axions escaping from neutron stars, and dark and usual matter interacting via the fifth dimension. We also overview the second flavor of hydrogen atoms: their existence was proven by analyzing atomic experiments and is also evidenced by the latest astrophysical observations of the 21 cm spectral line from the early Universe. While discussing non-particle models of the cause of dark matter effects, we refer to modified Newtonian dynamics and modifications of the strong equivalence principles. We also consider exotic compact objects, primordial black holes, and retardation effects. Finally, we review recent studies on the cause of dark energy effects. Specifically, we cover two disputes that arose in 2019 and 2020 on whether the observations of supernovas, previously interpreted as the proof of the existence of dark energy, could have alternative explanations. Besides, we note a study of 2021, where dark energy is substituted by a new hypothetical type of dark matter having a magnetic-type interaction. We also refer to the recent model of a system of nonrelativistic neutral gravitating particles providing an alternative explanation of the entire dynamics of the Universe expansion. without introducing dark energy or new gravitational degrees of freedom.

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Exploring multimessenger signals from heavy dark matter decay with EDGES   21-cm result and IceCube

Published Paper #: 957

Authors:, Ashadul Halder, Madhurima Pandey, Debasish Majumdar, Rupa Basu,

Journal: JCAP 10, 033 (2021)

url: http://arxiv.org/pdf/2105.14356v3.pdf

Abstract: The primordial heavy or superheavy dark matter that could be created during the reheating or preheating stage of the Universe can undergo QCD cascade decay process to produce leptons or $\gamma$ as end products. Although these could be rare decays, the energy involved in such decay process can influence 21-cm signal of hyperfine transition of neutral hydrogen during the reionization era. We explore in this work, possible multimessenger signals of such heavy dark matter decays. One of which could be the source of ultra high energy neutrino (of $\sim$ PeV energy regime) signals at IceCube detector whereas the other signal attributes to the cooling/heating of the baryons by the exchange of energy involved in this decay process and its consequent influence on 21-cm signal. The effect of evaporation of primordial black holes and baryon scattering with light cold dark matter are also included in relation to the evolution of the 21-cm signal temperature and their influence are also discussed.

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Model Independent Prediction of the Spectral Index of Primordial Quantum   Fluctuations

Published Paper #: 956

Authors:, Cesar Gomez, Raul Jimenez,

Journal: JCAP10(2021)052

url: http://arxiv.org/pdf/2103.10144v3.pdf

Abstract: One of the most important achievements of inflationary cosmology is to predict a departure from scale invariance of the power spectrum for scalar curvature cosmological fluctuations. This tilt is understood as a consequence of a quasi de Sitter classical equation of state describing the inflationary dark energy dominated era. Here, following previous work, we find a departure of scale invariance for the quantum Fisher information associated to de Sitter vacuum for scalar quantum spectator modes. This gives rise to a purely quantum cosmological tilt with a well defined dependence on energy scale. This quantum tilt is imprinted, in a scale dependent energy uncertainty for the spectator modes. The effective quasi de Sitter description of this model independent energy uncertainty uniquely sets the effective quasi de Sitter parameters at all energy scales. In particular, in the slow-roll regime characterized by an almost constant $\epsilon$, the quantum Fisher -- model independent -- prediction for the spectral index is $(1-n_s) = 0.0328$ ($n_s=0.9672$). Moreover, the energy scale dependence of the quantum cosmological tilt implies the existence of a cosmological phase transition at energies higher than the CMB scale where the tilt goes from red into blue. This strongly suggest the existence of a pre-inflationary phase where the effective scalaron contributes to the spectral index as normal relativistic matter and where the corresponding growth of the power spectrum can result in dark matter in the form of small mass primordial black holes. The source and features of the quantum cosmological tilt leading to these predictions are determined by the entanglement features of the de Sitter vacuum states.

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The quantum cosmological tilt and the origin of dark matter

Published Paper #: 955

Authors:, Cesar Gomez, Raul Jimenez,

Journal: JCAP10(2021)055

url: http://arxiv.org/pdf/2012.07883v2.pdf

Abstract: A promising candidate for cold dark matter is primordial black holes (PBH) formed from strong primordial quantum fluctuations. A necessary condition for the formation of PBH's is a change of sign in the tilt governing the anomalous scale invariance of the power spectrum from red at large scales into blue at small scales. Non-perturbative information on the dependence of the power spectrum tilt on energy scale can be extracted from the quantum Fisher information measuring the energy dependence of the quantum phases defining the de Sitter vacua. We show that this non-perturbative quantum tilt goes from a red tilted phase, at large scales, into a blue tilted phase at small scales converging to $n_s=2$ in the UV. This allows the formation of PBH's in the range of masses $\lesssim 10^{20} gr$.

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Gravitational waves from resonant amplification of curvature   perturbations during inflation

Published Paper #: 954

Authors:, Zhi-Zhang Peng, Chengjie Fu, Jing Liu, Zong-Kuan Guo, Rong-Gen Cai,

Journal: JCAP 10 (2021) 050

url: http://arxiv.org/pdf/2106.11816v2.pdf

Abstract: Parametric resonance in a single-field inflationary model with a periodic structure on the potential gives rise to curvature perturbations with large amplitudes on small scales, which could result in observable primordial black holes (PBHs) and concomitant gravitational waves (GWs) induced by curvature perturbations in the radiation-dominated era. In such a model, GWs associated with the PBH formation were investigated in Ref. [1]. In this paper, we consider a stochastic GW background sourced by inflaton perturbations resonantly amplified during inflation. We compute the energy spectra of induced GWs produced both during inflation and in the radiation-dominated era, and find that the peak of the energy spectrum of the former is much higher than that of the latter, but is located at a lower frequency. Moreover, the energy spectrum of induced GWs produced during inflation exhibits a unique oscillating character in the ultraviolet region. Both the stochastic GW backgrounds are expected to be detected by future space-based laser interferometers.

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Primordial black holes and stochastic gravitational wave background from   inflation with a noncanonical spectator field

Published Paper #: 953

Authors:, Rong-Gen Cai, Chao Chen, Chengjie Fu,

Journal: Phys. Rev. D 104, 083537 (2021)

url: http://arxiv.org/pdf/2108.03422v2.pdf

Abstract: We investigate the enhancement of the curvature perturbations in a single-field slow-roll inflation with a spectator scalar field kinetically coupled to the inflaton. The coupling term with a periodic function of inflaton triggers the exponential growth of the spectator field perturbations, which indirectly amplifies the curvature perturbations to produce a sizable abundance of primordial black holes (PBHs). This scenario is found to be insensitive to the inflationary background. We study two distinct populations of the stochastic gravitational wave background (SGWB) produced in this scenario, i.e., induced by the scalar perturbations during the inflationary era and the radiation-dominated era, respectively. With the appropriate choices of parameter space, we consider two PBH mass windows of great interest. One is PBHs of masses $\mathcal{O}(10^{-12})M_\odot$ that can be a vital component of dark matter, and the predicted total energy spectrum of SGWB shows a unique profile and is detectable by LISA and Taiji. The other is PBHs of masses $\mathcal{O}(10)M_\odot$ which can provide consistent explanation for the LIGO-Virgo events. More interestingly, the predicted gravitational wave signal from the radiation-dominated era may account for the NANOGrav results.

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Primordial black holes and stochastic gravitational wave background from   inflation with a noncanonical spectator field

Published Paper #: 953

Authors:, Rong-Gen Cai, Chao Chen, Chengjie Fu,

Journal: Phys. Rev. D 104, 083537 (2021)

url: http://arxiv.org/pdf/2108.03422v2.pdf

Abstract: We investigate the enhancement of the curvature perturbations in a single-field slow-roll inflation with a spectator scalar field kinetically coupled to the inflaton. The coupling term with a periodic function of inflaton triggers the exponential growth of the spectator field perturbations, which indirectly amplifies the curvature perturbations to produce a sizable abundance of primordial black holes (PBHs). This scenario is found to be insensitive to the inflationary background. We study two distinct populations of the stochastic gravitational wave background (SGWB) produced in this scenario, i.e., induced by the scalar perturbations during the inflationary era and the radiation-dominated era, respectively. With the appropriate choices of parameter space, we consider two PBH mass windows of great interest. One is PBHs of masses $\mathcal{O}(10^{-12})M_\odot$ that can be a vital component of dark matter, and the predicted total energy spectrum of SGWB shows a unique profile and is detectable by LISA and Taiji. The other is PBHs of masses $\mathcal{O}(10)M_\odot$ which can provide consistent explanation for the LIGO-Virgo events. More interestingly, the predicted gravitational wave signal from the radiation-dominated era may account for the NANOGrav results.

Keywords: ::

Future Constraints on Primordial Black Holes from XGIS-THESEUS

Published Paper #: 952

Authors:, Diptimoy Ghosh, Divya Sachdeva, Praniti Singh,

Journal: Phys. Rev. D 106, 023022 (2022)

url: http://arxiv.org/pdf/2110.03333v2.pdf

Abstract: Current observations allow Primordial Black Holes (PBHs) in asteroid mass range $10^{17}-10^{22}$ g to constitute the entire dark matter (DM) energy density (barring a small mass range constrained by 21 cm observations). In this work, we explore the possibility of probing PBH with masses $10^{17}-10^{19}\,{\rm g}$ via upcoming X and Gamma Imaging Spectrometer (XGIS) telescope array on-board the Transient High-Energy Sky and Early Universe Surveyor (THESEUS) mission. While our projected limits are comparable with those proposed in the literature for $10^{16}\,{\rm g}\,<\,M_{\mathrm{PBH}}\,<\,10^{17}\,{\rm g}$, we show that the XGIS-THESEUS mission can potentially provide the strongest bound for $10^{17} \mathrm{~g}<M_{\mathrm{PBH}} \lesssim 3\times 10^{18} \mathrm{~g}$ for non-rotating PBHs. The bounds become more stringent by nearly an order of magnitude for maximally rotating PBHs in the mass range $5\times10^{15}\,{\rm g}\,<\,M_{\rm PBH}\,\lesssim\,10^{19}\,{\rm g}$.

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Earth-mass primordial black hole mergers as sources for non-repeating   FRBs

Published Paper #: 951

Authors:, Can-Min Deng,

Journal: Physical Review D, 103, 123030 (2021)

url: http://arxiv.org/pdf/2110.08981v1.pdf

Abstract: Fast radio bursts (FRBs) are mysterious astronomical radio transients with extremely short intrinsic duration. Until now, the physical origins of them still remain elusive especially for the non-repeating FRBs. Strongly inspired by recent progress on possible evidence of Earth-mass primordial black holes, we revisit the model of Earth-mass primordial black holes mergers as sources for non-repeating FRBs. Under the null hypothesis that the observed non-repeating FRBs are originated from the mergers of Earth-mass primordial black holes, we analyzed four independent samples of non-repeating FRBs to study the model parameters i.e. the typical charge value $q_{\rm{c}}$ and the power index $\alpha$ of the charge distribution function of the primordial black hole population $\phi(q) \propto (q/q_{\rm{c}})^{-\alpha}$ which describe how the charge was distributed in the population. $q$ is the charge of   the hole in the unit of $\sqrt{G} M$, where $M$ is the mass of the hole. It turns out that this model can explain the observed data well. {Assuming the monochromatic mass spectrum for primordial black holes}, we get the average value of typical charge $\bar{q}_{\rm{c}}/10^{-5}=1.59^{+0.08}_{-0.18}$ and the power index $\bar{\alpha}=4.53^{+0.21}_{-0.14}$ by combining the fitting results given by four non-repeating FRB samples. The event rate of the non-repeating FRBs can be explained in the context of this model, if the abundance of the primordial black hole populations with charge $q \gtrsim 10^{-6}$ is larger than $10^{-5}$ which is far below the upper limit given by current observations for the abundance of Earth-mass primordial black holes. In the future, simultaneous detection of FRBs and high frequency gravitational waves produced by mergers of Earth-mass primordial black holes may directly confirm or deny this model.

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Long-wavelength non-linear perturbations of a complex scalar field

Published Paper #: 950

Authors:, Luis E. Padilla, Juan Carlos Hidalgo, Darío Núñez,

Journal: Phys. Rev. D 104, 083513 (2021)

url: http://arxiv.org/pdf/2107.01187v3.pdf

Abstract: We study the evolution of nonlinear superhorizon perturbations in a universe dominated by a complex scalar field. The analysis is performed adopting the gradient expansion approach, in the constant mean curvature slicing. We derive general solutions valid to second order in the ratio $H^{-1}/L$ for scalar field inhomogeneities of size $L$ subject to an arbitrary canonical potential. We work out explicit solutions for the quadratic and the quartic potentials, and discuss their relevance in setting initial conditions required for the simulations of Primordial Black Hole formation.

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Strong clustering of primordial black holes from Affleck-Dine mechanism

Published Paper #: 949

Authors:, Masahiro Kawasaki, Kai Murai, Hiromasa Nakatsuka,

Journal: JCAP 10 (2021) 025

url: http://arxiv.org/pdf/2107.03580v3.pdf

Abstract: Primordial black hole (PBH) is a fascinating candidate for the origin of binary merger events observed by LIGO-Virgo collaboration. The spatial distribution of PBHs at formation is an important feature to estimate the merger rate. We investigate the clustering of PBHs formed by Affleck-Dine (AD) baryogenesis, where dense baryon bubbles collapse to form PBHs. We found that formed PBHs show a strong clustering due to the stochastic dynamics of the AD field. Including the clustering, we evaluate the merger rate and isocurvature perturbations of PBHs, which show significant deviations from those without clustering.

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Prospects for probing gravitational waves from primordial black hole   binaries

Published Paper #: 948

Authors:, Oriol Pujolas, Ville Vaskonen, Hardi Veermäe,

Journal: Phys.Rev.D 104 (2021) 8, 083521

url: http://arxiv.org/pdf/2107.03379v2.pdf

Abstract: We study the prospects of future gravitational wave (GW) detectors in probing primordial black hole (PBH) binaries. We show that across a broad mass range from $10^{-5}M_\odot$ to $10^7M_\odot$, future GW interferometers provide a potential probe of the PBH abundance that is more sensitive than any currently existing experiment. In particular, we find that galactic PBH binaries with masses as low as $10^{-5}M_\odot$ may be probed with ET, AEDGE and LISA by searching for nearly monochromatic continuous GW signals. Such searches could independently test the PBH interpretation of the ultrashort microlensing events observed by OGLE. We also consider the possibility of observing GWs from asteroid mass PBH binaries through graviton-photon conversion.

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Mechanism of primordial black holes production and secondary   gravitational waves in $α$-attractor Galileon inflationary scenario

Published Paper #: 947

Authors:, Zeinab Teimoori, Kazem Rezazadeh, Mariwan Ahmed Rasheed, Kayoomars Karami,

Journal: JCAP10(2021)018

url: http://arxiv.org/pdf/2107.07620v2.pdf

Abstract: We study the process of the Primordial Black Holes (PBHs) production in the novel framework, namely $\alpha$-attractor Galileon inflation (G-inflation) model. In our framework, we take the Galileon function as $G(\phi)=G_{I}(\phi)\left(1+G_{II}(\phi)\right)$, where the part $G_{I}(\phi)$ is motivated from the $\alpha$-attractor inflationary scenario in its original non-canonical frame, and it ensures for the model to be consistent with the Planck 2018 observations at the CMB scales. The part $G_{II}(\phi)$ is invoked to enhance the curvature perturbations at some smaller scales which in turn gives rise to PBHs formation. By fine-tuning of the model parameters, we find three parameter sets which successfully produce a sufficiently large peak in the curvature power spectrum. We show that these parameter sets produce PBHs with masses ${\cal O}(10)M_\odot$, ${\cal O}(10^{-5})M_\odot$, and ${\cal O}(10^{-13})M_\odot$ which can explain the LIGO events, the ultrashort-timescale microlensing events in OGLE data, and around $0.98\%$ of the current Dark Matter (DM) content of the universe, respectively. Additionally, we study the secondary Gravitational Waves (GWs) in our setup and show that our model anticipates the peak of their present fractional energy density as $\Omega_{GW0} \sim 10^{-8}$ for all the three parameter sets, but at different frequencies. These predictions can be located well inside the sensitivity region of some GWs detectors, and therefore the compatibility of our model can be assessed in light of the future data. We further estimate the tilts of the included GWs spectrum in the different ranges of frequency, and confirm that spectrum follows the power-law relation $\Omega_{GW0}\sim f^{n}$ in those frequency bands.

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Primordial black holes formation in the inflationary model with   field-dependent kinetic term for quartic and natural potentials

Published Paper #: 946

Authors:, Milad Solbi, Kayoomars Karami,

Journal: Eur. Phys. J. C 81, 884 (2021)

url: http://arxiv.org/pdf/2106.02863v2.pdf

Abstract: Within the framework of inflationary model with field-dependent kinetic term for quartic and natural potentials, we investigate generation of the primordial black holes (PBHs) and induced gravitational waves (GWs). In this setup, we consider a kinetic function as $G(\phi)=g_I(\phi)\big(1+g_{II}(\phi)\big)$ and show that in the presence of first term $g_I(\phi)$ both quartic and natural potentials, in contrast to the standard model of inflation, can be consistent, with the 68\% CL of Planck observations. Besides, the second term $g_{II}(\phi)$ can cause a significant enhancement in the primordial curvature perturbations at the small scales which results the PBHs formation. For the both potentials, we obtain an enhancement in the scalar power spectrum at the scales $k\sim10^{12}~\rm Mpc^{-1}$, $10^{8}~\rm Mpc^{-1}$, and $10^{5}~\rm Mpc^{-1}$, which causes PBHs production in mass scales around $10^{-13}M_{\odot}$, $10^{-5}M_{\odot}$, and $10 M_{\odot}$, respectively. Observational constraints confirm that PBHs with a mass scale of $10^{-13}M_{\odot}$ can constitute the total of dark matter in the universe. Furthermore, we estimate the energy density parameter of induced GWs which can be examined by the observation. Also we conclude that it can be parametrized as a power-law function $\Omega_{\rm GW}\sim (f/f_c)^n$, where the power index equals $n=3-2/\ln(f_c/f)$ in the infrared limit $f\ll f_{c}$.

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Bayesian Forecasts for Dark Matter Substructure Searches with Mock   Pulsar Timing Data

Published Paper #: 945

Authors:, Vincent S. H. Lee, Stephen R. Taylor, Tanner Trickle, Kathryn M. Zurek,

Journal: Journal of Cosmology and Astroparticle Physics 08 (2021) 025

url: http://arxiv.org/pdf/2104.05717v2.pdf

Abstract: Dark matter substructure, such as primordial black holes (PBHs) and axion miniclusters, can induce phase shifts in pulsar timing arrays (PTAs) measurements due to gravitational effects. In order to gain a more realistic forecast for the detectability of such models of dark matter with PTAs, we propose a Bayesian inference framework to search for phase shifts generated by PBHs and perform the analysis on mock PTA data. For most PBH masses the constraints on the dark matter abundance agree with previous (frequentist) analyses (without mock data) to $\mathcal{O}(1)$ factors. This further motivates a dedicated search for PBHs (and dense small scale structures) in the mass range from $10^{-8}\,M_{\odot}$ to well above $10^2\,M_{\odot}$ with the Square Kilometer Array. Moreover, with a more optimistic set of timing parameters, future PTAs are predicted to constrain PBHs down to $10^{-11}\,M_{\odot}$. Lastly, we discuss the impact of backgrounds, such as Supermassive Black Hole Mergers, on detection prospects, suggesting a future program to separate a dark matter signal from other astrophysical sources.

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Possibility of Primordial black holes Collision with Earth and the   Consequences

Published Paper #: 944

Authors:, Sohrab Rahvar,

Journal: Monthly Notices of the Royal Astronomical Society 507, 914 (2021)

url: http://arxiv.org/pdf/2107.11139v2.pdf

Abstract: In the context of the existence of primordial black holes (PBHs), they may compose a fraction of the dark matter of the Universe. Assuming that PBHs fill the dark content of the Milky Way Galaxy in the Galactic halo and dark disk, we calculate the probability of collision of the PBHs with Earth. This collision has different consequences as heating the interior of the earth through dynamical friction and accretion processes. In this work, we calculate the rate of collisions and a fraction of black holes that can be trapped inside the earth. Finally, we compare the danger of PBH collision with the asteroid impacts on Earth.

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CMB $μT$ cross-correlations as a probe of PBH scenarios

Published Paper #: 943

Authors:, Ogan Özsoy, Gianmassimo Tasinato,

Journal: Phys. Rev. D 104, 043526 (2021)

url: http://arxiv.org/pdf/2104.12792v2.pdf

Abstract: We propose a new method for probing inflationary models of primordial black hole (PBH) production, using only CMB physics at relatively large scales. In PBH scenarios, the primordial power spectrum profile for curvature perturbations is characterized by a pronounced dip, followed by a rapid growth towards small scales, leading to a peak responsible for PBH formation. We focus on scales around the dip that are well separated from the peak to analytically compute expressions for the curvature power spectrum and bispectrum. The size of the squeezed bispectrum is enhanced at the position of the dip, and it acquires a characteristic scale dependence that can be probed by cross-correlating CMB $\mu$-distortions and temperature fluctuations. We quantitatively study the properties of such cross-correlations and how they depend on the underlying model, discussing how they can be tested by the next generation of CMB $\mu$-distortion experiments. This method allows one to experimentally probe inflationary PBH scenarios using well-understood CMB physics, without considering non-linearities associated with PBH formation and evolution.

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Black hole induced spins from hyperbolic encounters in dense clusters

Published Paper #: 942

Authors:, Santiago Jaraba, Juan Garcia-Bellido,

Journal: Physics of the Dark Universe 34 (2021) 100882

url: http://arxiv.org/pdf/2106.01436v2.pdf

Abstract: The black holes that have been detected via gravitational waves (GW) can have either astrophysical or primordial origin. Some GW events show significant spin for one of the components and have been assumed to be astrophysical, since primordial black holes are generated with very low spins. However, it is worth studying if they can increase their spin throughout the evolution of the universe. Possible mechanisms that have already been explored are multiple black hole mergers and gas accretion. We propose here a new mechanism that can occur in dense clusters of black holes: the spin-up of primordial black holes when they are involved in close hyperbolic encounters. We explore this effect numerically with the Einstein Toolkit for different initial conditions, including variable mass ratios. For equal masses, there is a maximum spin that can be induced on the black holes, $\chi = a/m \leq 0.2$. We find however that for large mass ratios one can attain spins up to $\chi \simeq 0.8$, where the highest spin is induced on the most massive black hole. For small induced spins we provide simple analytical expressions that depend on the relative velocity and impact parameter.

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Axion-Sterile-Neutrino Dark Matter

Published Paper #: 941

Authors:, Alberto Salvio, Simone Scollo,

Journal: Universe 7 (2021) 354

url: http://arxiv.org/pdf/2104.01334v3.pdf

Abstract: Extending the Standard Model with three right-handed neutrinos and a simple QCD axion sector can account for neutrino oscillations, dark matter and baryon asymmetry; at the same time, it solves the strong CP problem, stabilizes the electroweak vacuum and can implement critical Higgs inflation (satisfying all current observational bounds). We perform here a general analysis of dark matter (DM) in such a model, which we call the $a\nu$MSM. Although critical Higgs inflation features a (quasi) inflection point of the inflaton potential we show that DM cannot receive a contribution from primordial black holes in the $a\nu$MSM. This leads to a multicomponent axion-sterile-neutrino DM and allows us to relate the axion parameters, such as the axion decay constant, to the neutrino parameters. We include several DM production mechanisms: the axion production via misalignment and decay of topological defects as well as the sterile-neutrino production through the resonant and non-resonant mechanisms and in the recently proposed CPT-symmetric universe.

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Perturbed recombination from inhomogeneous photon injection and   application to accreting primordial black holes

Published Paper #: 940

Authors:, Trey W. Jensen, Yacine Ali-Haïmoud,

Journal: Phys. Rev. D 104, 063534 (2021)

url: http://arxiv.org/pdf/2106.10266v2.pdf

Abstract: Exotic electromagnetic energy injection in the early Universe may alter cosmological recombination, and ultimately cosmic microwave background (CMB) anisotropies. Moreover, if energy injection is inhomogeneous, it may induce a spatially-varying ionization fraction, and non-Gaussianity in the CMB. The observability of these signals, however, is contingent upon how far the injected particles propagate and deposit their energy into the primordial plasma, relative to the characteristic scale of energy injection fluctuations. In this study we inspect the spatial properties of energy deposition and perturbed recombination resulting from an inhomogeneous energy injection of sub-10 MeV photons, relevant to accreting primordial black holes (PBHs). We develop a novel Monte-Carlo radiation transport code accounting for all relevant photon interactions in this energy range, and including secondary electron energy deposition efficiency through a new analytic approximation. For a specified injected photon spectrum, the code outputs an injection-to-deposition Green's function depending on time and distance from the injection point. Combining this output with a linearized solution of the perturbed recombination problem, we derive time- and scale-dependent deposition-to-ionization Green's functions. We apply this general framework to accreting PBHs, whose luminosity is strongly spatially modulated by supersonic relative velocities between cold dark matter and baryons. We find that the resulting spatial fluctuations of the free-electron fraction are of the same magnitude as its mean deviation from standard recombination, from which current CMB power spectra constraints are derived. This work suggests that the sensitivity to accreting PBHs might be substantially improved by propagating these inhomogeneities to CMB anisotropy power spectra and non-Gaussian statistics, which we study in subsequent papers.

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Radio signatures from encounters between Neutron Stars and QCD-Axion   Minihalos around Primordial Black Holes

Published Paper #: 939

Authors:, Sami Nurmi, Enrico D. Schiappacasse, Tsutomu T. Yanagida,

Journal: JCAP 09 (2021) 004

url: http://arxiv.org/pdf/2102.05680v2.pdf

Abstract: Probing the QCD axion dark matter (DM) hypothesis is extremely challenging as the axion interacts very weakly with Standard Model particles. We propose a new avenue to test the QCD axion DM via transient radio signatures coming from encounters between neutron stars (NSs) and axion minihalos around primordial black holes (PBHs). We consider a general QCD axion scenario in which the PQ symmetry breaking occurs before (or during) inflation coexisting with a small fraction of DM in the form of PBHs. The PBHs will unavoidably acquire around them axion minihalos with the typical length scale of parsecs. The axion density in the minihalos may be much higher than the local DM density, and the presence of these compact objects in the Milky Way today provides a novel chance for testing the axion DM hypothesis. We study the evolution of the minihalo mass distribution in the Galaxy accounting for tidal forces and estimate the encounter rate between NSs and the dressed PBHs. We find that the encounters give rise to transient line-like emission of radio frequency photons produced by the resonant axion-photon conversion in the NS magnetosphere and the characteristic signal could be detectable with the sensitivity of current and prospective radio telescopes. It would be important to investigate in detail search strategies for such signals which would provide a novel pathway for QCD axion detection.

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Axion Dark Matter in the Time of Primordial Black Holes

Published Paper #: 938

Authors:, Nicolás Bernal, Fazlollah Hajkarim, Yong Xu,

Journal: Phys. Rev. D 104, 075007 (2021)

url: http://arxiv.org/pdf/2107.13575v3.pdf

Abstract: We investigate the production of QCD axion dark matter in a nonstandard cosmological era triggered by primordial black holes (PBHs) that fully evaporate before the onset of BBN. Even if PBHs cannot emit the whole axion cold dark matter abundance through Hawking radiation, they can have a strong impact on the dark matter produced via the misalignment mechanism. First, the oscillation temperature of axions reduces if there is a PBH dominated era, and second, PBH evaporation injects entropy to the standard model, diluting the axion relic abundance originally produced. The axion window is therefore enlarged, reaching masses as light as $\sim 10^{-8}$ eV and decay constants as large as $f_{a}\sim 10^{14}$ GeV without fine tuning the misalignment angle. Such small masses are in the reach of future detectors as ABRACADABRA, KLASH, and ADMX, if the axion couples to photons. Additionally, the axions radiated by PBHs contribute to $\Delta N_\text{eff}$ within the projected reach of the future CMB Stage 4 experiment.

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Mass classification of dark matter perturbers of stellar tidal streams

Published Paper #: 937

Authors:, Francesco Montanari, Juan García-Bellido,

Journal: Physics of the Dark Universe 35 (2022) 100978

url: http://arxiv.org/pdf/2012.11482v2.pdf

Abstract: Stellar streams formed by tidal stripping of progenitors orbiting around the Milky Way are expected to be perturbed by encounters with dark matter subhalos. Recent studies have shown that they are an excellent proxy to infer properties of the perturbers, such as their mass. Here we present two different methodologies that make use of the fully non-Gaussian density distribution of stellar streams: a Bayesian model selection based on the probability density function (PDF) of stellar density, and a likelihood-free gradient boosting classifier. While the schemes do not assume a specific dark matter model, we are mainly interested in discerning the primordial black holes cold dark matter (PBH CDM) hypothesis form the standard particle dark matter one. Therefore, as an application we forecast model selection strength of evidence for cold dark matter clusters of masses $10^3$ - $10^5 M_{\odot}$ and $10^5$ - $10^9 M_{\odot}$, based on a GD-1-like stellar stream and including realistic observational errors. Evidence for the smaller mass range, so far under-explored, is particularly interesting for PBH CDM. We expect weak to strong evidence for model selection based on the PDF analysis, depending on the fiducial model. Instead, the gradient boosting model is a highly efficient classifier (99\% accuracy) for all mass ranges here considered. As a further test of the robustness of the method, we reach similar conclusions when performing forecasts further dividing the largest mass range into $10^5$ - $10^7 M_{\odot}$ and $10^7$ - $10^9 M_{\odot}$ ranges.

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Gravitational microlensing constraints on primordial black holes by   Euclid

Published Paper #: 936

Authors:, Lindita Hamolli, Mimoza Hafizi, Francesco De Paolis, Achille A. Nucita,

Journal: published in Astrophysic and Space Science, 2021

url: http://arxiv.org/pdf/2109.04857v1.pdf

Abstract: Primordial black holes (PBHs) may form in the early stages of the Universe via the collapse of large density perturbations. Depending on the formation mechanism, PBHs may exist and populate today the galactic halos and have masses in a wide range, from about 10^{-14}Msun up to thousands, or more, of solar masses. Gravitational microlensing is the most robust and powerful method to constrain primordial black holes (PBHs), since it does not require that the lensing objects be directly visible. We calculate the optical depth and the rate of microlensing events caused by PBHs eventually distributed in the Milky Way halo, towards some selected directions of observation. Then we discuss the capability of Euclid, a space-based telescope which might perform microlensing observations at the end of its nominal mission, to probe the PBH populations in the Galactic halo.

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Double-peaked inflation model: Scalar induced gravitational waves and   primordial-black-hole suppression from primordial non-Gaussianity

Published Paper #: 935

Authors:, Fengge Zhang, Jiong Lin, Yizhou Lu,

Journal: Phys. Rev. D 104, 063515 (2021)

url: http://arxiv.org/pdf/2106.10792v2.pdf

Abstract: A significant abundance of primordial black hole (PBH) dark matter can be produced by curvature perturbations with power spectrum $\Delta_\zeta^2(k_{\mathrm{peak}})\sim \mathcal{O}(10^{-2})$ at small scales, associated with the generation of observable scalar induced gravitational waves (SIGWs). However, the primordial non-Gaussianity may play a non-negligible role, which is not usually considered. We propose two inflation models that predict double peaks of order $\mathcal{O}(10^{-2})$ in the power spectrum and study the effects of primordial non-Gaussianity on PBHs and SIGWs. This model is driven by a power-law potential, and has a noncanonical kinetic term whose coupling function admits two peaks. By field-redefinition, it can be recast into a canonical inflation model with two quasi-inflection points in the potential. We find that the PBH abundance will be altered saliently if non-Gaussianity parameter satisfies $|f_{\mathrm{NL}}(k_{\text{peak}},k_{\text{peak}},k_{\text{peak}})|\gtrsim \Delta^2_{\zeta}(k_{\mathrm{peak}})/(23\delta^3_c) \sim \mathcal{O}(10^{-2})$. Whether the PBH abundance is suppressed or enhanced depends on the $f_{\mathrm{NL}}$ being positive or negative, respectively. In our model, non-Gaussianity parameter $f_{\mathrm{NL}}(k_{\mathrm{peak}},k_{\mathrm{peak}},k_{\mathrm{peak}})\sim \mathcal{O}(1)$ takes positive sign, thus PBH abundance is suppressed dramatically. On the contrary, SIGWs are insensitive to primordial non-Gaussianity and hardly affected, so they are still within the sensitivities of space-based GWs observatories and Square Kilometer Array.

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On mass spectra of primordial black holes

Published Paper #: 934

Authors:, Alexander A. Kirillov, Sergey G. Rubin,

Journal: Front. Astron. Space Sci. 8 (2021) 777661

url: http://arxiv.org/pdf/2109.02446v1.pdf

Abstract: Evidences for the primordial black holes (PBH) presence in the early Universe renew permanently. New limits on their mass spectrum challenge existing models of PBH formation. One of the known model is based on the closed walls collapse after the inflationary epoch. Its intrinsic feature is multiple production of small mass PBH which might contradict observations in the nearest future. We show that the mechanism of walls collapse can be applied to produce substantially different PBH mass spectra if one takes into account the classical motion of scalar fields together with their quantum fluctuations at the inflationary stage.

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Search for gravitational waves from the coalescence of sub-solar mass   binaries in the first half of Advanced LIGO and Virgo's third observing run

Published Paper #: 933

Authors:, Alexander H. Nitz, Yi-Fan Wang,

Journal: Phys. Rev. Lett. 127, 151101 (2021)

url: http://arxiv.org/pdf/2106.08979v3.pdf

Abstract: We present a search for gravitational waves from the coalescence of sub-solar mass black hole binaries using data from the first half of Advanced LIGO and Virgo's third observing run. The observation of a sub-solar mass black hole merger may be an indication of primordial origin; primordial black holes may contribute to the dark matter distribution. We search for black hole mergers where the primary mass is $0.1-7 M_{\odot}$ and the secondary mass is $0.1-1 M_{\odot}$. A variety of models predict the production and coalescence of binaries containing primordial black holes; some involve dynamical assembly which may allow for residual eccentricity to be observed. For component masses $>0.5 M_{\odot}$, we also search for sources in eccentric orbits, measured at a reference gravitational-wave frequency of 10 Hz, up to $e_{10}\sim 0.3$. We find no convincing candidates and place new upper limits on the rate of primordial black hole mergers. The merger rate of 0.5-0.5 (1.0-1.0)~$M_{\odot}$ sources is $<7100~(1200)$ Gpc$^{-3}$yr$^{-1}$. Our limits are $\sim3-4$ times more constraining than prior analyses. Finally, we demonstrate how our limits can be used to constrain arbitrary models of the primordial black hole mass distribution and merger rate.

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Non-Gaussian tail of the curvature perturbation in stochastic   ultra-slow-roll inflation: implications for primordial black hole production

Published Paper #: 932

Authors:, Daniel G. Figueroa, Sami Raatikainen, Syksy Rasanen, Eemeli Tomberg,

Journal: Phys. Rev. Lett. 127, 101302 (2021)

url: http://arxiv.org/pdf/2012.06551v2.pdf

Abstract: We consider quantum diffusion in ultra-slow-roll (USR) inflation. Using the $\Delta N$ formalism, we present the first stochastic calculation of the probability distribution $P(\mathcal{R})$ of the curvature perturbation during USR. We capture the non-linearity of the system, solving the coupled evolution of the coarse-grained background with random kicks from the short wavelength modes, simultaneously with the mode evolution around the stochastic background. This leads to a non-Markovian process from which we determine the highly non-Gaussian tail of $P(\mathcal{R})$. Studying the production of primordial black holes in a viable model, we find that stochastic effects during USR increase their abundance by a factor $\sim 10^5$ compared to the Gaussian approximation.

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Constraining the Initial Primordial Black Hole Clustering with   CMB-distortion

Published Paper #: 931

Authors:, V. De Luca, G. Franciolini, A. Riotto,

Journal: Phys. Rev. D 104, 063526 (2021)

url: http://arxiv.org/pdf/2103.16369v2.pdf

Abstract: The merger rate of primordial black holes depends on their initial clustering. In the absence of primordial non-Gaussianity correlating short and large-scales, primordial black holes are distributed \`a la Poisson at the time of their formation. However, primordial non-Gaussianity of the local-type may correlate primordial black holes on large-scales. We show that future experiments looking for CMB $\mu$-distortion would test the hypothesis of initial primordial black hole clustering induced by local non-Gaussianity, while existing limits already show that significant non-Gaussianity is necessary to induce primordial black hole clustering.

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In-depth analysis of the clustering of dark matter particles around   primordial black holes I: density profiles

Published Paper #: 930

Authors:, Mathieu Boudaud, Thomas Lacroix, Martin Stref, Julien Lavalle, Pierre Salati,

Journal: JCAP08(2021)053

url: http://arxiv.org/pdf/2106.07480v2.pdf

Abstract: Primordial black holes may have been produced in the early stages of the thermal history of the Universe after cosmic inflation. If so, dark matter in the form of elementary particles can be subsequently accreted around these objects, in particular when it gets non-relativistic and further streams freely in the primordial plasma. A dark matter mini-spike builds up gradually around each black hole, with density orders of magnitude larger than the cosmological one. We improve upon previous work by carefully inspecting the computation of the mini-spike radial profile as a function of black hole mass, dark matter particle mass and temperature of kinetic decoupling. We identify a phase-space contribution that has been overlooked and that leads to changes in the final results. We also derive complementary analytical formulae using convenient asymptotic regimes, which allows us to bring out peculiar power-law behaviors for which we provide tentative physical explanations.

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Axion-like particles from primordial black holes shining through the   Universe

Published Paper #: 929

Authors:, Francesco Schiavone, Daniele Montanino, Alessandro Mirizzi, Francesco Capozzi,

Journal: JCAP 08 (2021), p. 063

url: http://arxiv.org/pdf/2107.03420v2.pdf

Abstract: We consider a cosmological scenario in which the very early Universe experienced a transient epoch of matter domination due to the formation of a large population of primordial black holes (PBHs) with masses $M \lesssim 10^{9}\,\textrm{g}$, that evaporate before Big Bang nucleosynthesis. In this context, Hawking radiation would be a non-thermal mechanism to produce a cosmic background of axion-like particles (ALPs). We assume the minimal scenario in which these ALPs couple only with photons. In the case of ultralight ALPs ($m_a \lesssim 10^{-9}\,\textrm{eV}$) the cosmic magnetic fields might trigger ALP-photon conversions, while for masses $m_a \gtrsim 10\,\textrm{eV}$ spontaneous ALP decay in photon pairs would be effective. We investigate the impact of these mechanisms on the cosmic X-ray background, on the excess in X-ray luminosity in Galaxy Clusters, and on the process of cosmic reionization.

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Spins of primordial black holes formed in different cosmological   scenarios

Published Paper #: 928

Authors:, Marcos M. Flores, Alexander Kusenko,

Journal: Phys. Rev. D 104, 063008 (2021)

url: http://arxiv.org/pdf/2106.03237v2.pdf

Abstract: Primordial black holes (PBHs) could account for all or part of dark matter, as well as for some LIGO events. We discuss the spins of primordial black holes produced in different cosmological scenarios, with the emphasis on recently discovered possibilities. PBHs produced as a horizon-size collapse of density perturbations are known to have very small spins. In contrast, PBHs resulting from assembly of matterlike objects (particles, Q-balls, oscillons, etc.) can have large or small spins depending on their formation history and the efficiency of radiative cooling. We show that scalar radiation can remove the angular momentum very efficiently, leading to slowly rotating PBHs in those scenarios for which the radiative cooling is important. Gravitational waves astronomy offers an opportunity to determine the spins of black holes, opening a new window on the early Universe if, indeed, some black holes have primordial origin.

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The Formation Probability of Primordial Black Holes

Published Paper #: 927

Authors:, Matteo Biagetti, Valerio De Luca, Gabriele Franciolini, Alex Kehagias, Antonio Riotto,

Journal: Phys.Lett.B 820 (2021) 136602

url: http://arxiv.org/pdf/2105.07810v2.pdf

Abstract: We calculate the exact formation probability of primordial black holes generated during the collapse at horizon re-entry of large fluctuations produced during inflation, such as those ascribed to a period of ultra-slow-roll. We show that it interpolates between a Gaussian at small values of the average density contrast and a Cauchy probability distribution at large values. The corresponding abundance of primordial black holes may be larger than the Gaussian one by several orders of magnitude. The mass function is also shifted towards larger masses.

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A topic review on probing primordial black hole dark matter with scalar   induced gravitational waves

Published Paper #: 926

Authors:, Chen Yuan, Qing-Guo Huang,

Journal: iScience 24, 102860 (2021)

url: http://arxiv.org/pdf/2103.04739v2.pdf

Abstract: Primordial black holes (PBHs) are supposed to form from the collapse of over-densed regions generated by large scalar curvature perturbations in the radiation dominated era. Despite decades of various independent observations, the nature of dark matter (DM) remains highly puzzling. Recently, PBH DM have aroused interest since they provide an attracting explanation to the merger events of binary black holes discovered by LIGO/VIRGO and may play an important role on DM. During the formation of PBH, gravitational waves will be sourced by linear scalar perturbations at second-order, known as the scalar-induced gravitational waves (SIGWs), which provides a new way to hunt for PBH DM. This topic review mainly focus on the physics about SIGWs accompanying the formation of PBH DM.

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Primordial black holes and induced gravitational waves in $k$-inflation

Published Paper #: 925

Authors:, Milad Solbi, Kayoomars Karami,

Journal: JCAP 08 (2021) 056

url: http://arxiv.org/pdf/2102.05651v3.pdf

Abstract: Recent observational constraints indicate that primordial black holes (PBHs) with the mass scale $\sim 10^{-12}M_{\odot}$ can explain most of dark matter in the Universe. To produce this kind of PBHs, we need an enhance in the primordial scalar curvature perturbations to the order of ${\mathcal{O}(10^{-2})}$ at the scale $ k \sim 10^{12}~\rm Mpc^{-1}$. Here, we investigate the production of PBHs and induced gravitational waves (GWs) in the framework of \textbf{$k$-inflation}. We solve numerically the Mukhanov-Sasaki equation to obtain the primordial scalar power spectrum. In addition, we estimate the PBHs abundance $f_{\text{PBH}}^{\text{peak}}$ as well as the energy density parameter $\Omega_{\rm GW,0}$ of induced GWs. Interestingly enough is that for a special set of model parameters, we estimate the mass scale and the abundance of PBHs as $\sim{\cal O}(10^{-13})M_{\odot}$ and $f_{\text{PBH}}^{\text{peak}}=0.96$, respectively. This confirms that the mechanism of PBHs production in our inflationary model can justify most of dark matter. Furthermore, we evaluate the GWs energy density parameter and conclude that it behaves like a power-law function $\Omega_{\rm GW}\sim (f/f_c)^n$ where in the infrared limit $f\ll f_{c}$, the power index reads $n=3-2/\ln(f_c/f)$.

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Gravitational Waves and Possible Fast Radio Bursts from Axion Clumps

Published Paper #: 924

Authors:, Sichun Sun, Yun-Long Zhang,

Journal: Phys. Rev. D 104, 103009 (2021)

url: http://arxiv.org/pdf/2003.10527v3.pdf

Abstract: The axion objects such as axion mini-clusters and axion clouds around spinning black holes induce parametric resonances of electromagnetic waves through the axion-photon interaction. In particular, it has been known that the resonances from the axion with the mass around $10^{-6}$eV may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational waves, which we call the fast gravitational wave bursts (FGBs), are generated from axion clumps with the presence of gravitational Chern-Simons (CS) coupling. The typical frequency is half of the axion mass, which in general can range from kHz to GHz. We also discuss the secondary gravitational wave production associated with FRB, as well as the possible host objects of the axion clouds, such as primordial black holes with typical masses around $10^{-5}M_{\odot}$. Future detections of FGBs together with the observed FRBs are expected to provide more evidence for the axion.

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