Uncertainties in primordial black-hole constraints on the primordial   power spectrum

Published Paper #: 542

Authors:, Yashar Akrami, Florian Kuhnel, Marit Sandstad,

Journal: Physics of the Dark Universe 19 (2018) 124-128

url: http://arxiv.org/pdf/1611.10069v4.pdf

Abstract: The existence (and abundance) of primordial black holes (PBHs) is governed by the power spectrum of primordial perturbations generated during inflation. So far no PBHs have been observed, and instead, increasingly stringent bounds on their existence at different scales have been obtained. Up until recently, this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by cosmological observations. We first point out that the simple translation of the PBH non-observation bounds into constraints on the primordial power spectrum is inaccurate as it fails to include realistic aspects of PBH formation and evolution. We then demonstrate, by studying two examples of uncertainties from the effects of critical and non-spherical collapse, that even though they may seem small, they have important implications for the usefulness of the constraints. In particular, we point out that the uncertainty induced by non-spherical collapse may be much larger than the difference between particular bounds from PBH non-observations and the general maximum cap stemming from the condition $\Omega \leq 1$ on the dark-matter density in the form of PBHs. We therefore make the cautious suggestion of applying only the overall maximum dark-matter constraint to models of early Universe, as this requirement seems to currently provide a more reliable constraint, which better reflects our current lack of detailed knowledge of PBH formation. These, and other effects, such as merging, clustering and accretion, may also loosen constraints from non-observations of other primordial compact objects such as ultra-compact minihalos of dark matter.

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Primordial Black Holes from Polynomial Potentials in Single Field   Inflation

Published Paper #: 541

Authors:, Mark P. Hertzberg, Masaki Yamada,

Journal: Phys. Rev. D 97, 083509 (2018)

url: http://arxiv.org/pdf/1712.09750v2.pdf

Abstract: Within canonical single field inflation models, we provide a method to reverse engineer and reconstruct the inflaton potential from a given power spectrum. This is not only a useful tool to find a potential from observational constraints, but also gives insight into how to generate a large amplitude spike in density perturbations, especially those that may lead to primordial black holes (PBHs). In accord with other works, we find that the usual slow-roll conditions need to be violated in order to generate a significant spike in the spectrum. We find that a way to achieve a very large amplitude spike in single field models is for the classical roll of the inflaton to over-shoot a local minimum during inflation. We provide an example of a quintic polynomial potential that implements this idea and leads to the observed spectral index, observed amplitude of fluctuations on large scales, significant PBH formation on small scales, and is compatible with other observational constraints. We quantify how much fine-tuning is required to achieve this in a family of random polynomial potentials, which may be useful to estimate the probability of PBH formation in the string landscape.

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Collisions in Primordial Star Clusters: Formation Pathway for   intermediate mass black holes

Published Paper #: 540

Authors:, B. Reinoso, D. R. G. Schleicher, M. Fellhauer, R. S. Klessen, T. C. N. Boekholt,

Journal: A&A 614, A14 (2018)

url: http://arxiv.org/pdf/1801.05891v2.pdf

Abstract: Collisions were suggested to potentially play a role in the formation of massive stars in present day clusters, and have likely been relevant during the formation of massive stars and intermediate mass black holes within the first star clusters. In the early Universe, the first stellar clusters were particularly dense, as fragmentation typically only occurred at densities above $10^9$cm$^{-3}$, and the radii of the protostars were enhanced due to the larger accretion rates, suggesting a potentially more relevant role of stellar collisions. We present here a detailed parameter study to assess how the number of collisions as well as the mass growth of the most massive object depends on the properties of the cluster, and we characterize the time evolution with three effective parameters, the time when most collisions occur, the duration of the collisions period, as well as the normalization required to obtain the total number of collisions. We apply our results to typical Population III (Pop.III) clusters of about $1000$M$_\odot$, finding that a moderate enhancement of the mass of the most massive star by a factor of a few can be expected. For more massive Pop.III clusters as expected in the first atomic cooling halos, we expect a more significant enhancement by a factor of $15-32$. We therefore conclude that collisions in massive Pop.III clusters were likely relevant to form the first intermediate mass black holes.

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Primordial Black Holes as Dark Matter: Converting Constraints from   Monochromatic to Extended Mass Distributions

Published Paper #: 539

Authors:, Nicola Bellomo, José Luis Bernal, Alvise Raccanelli, Licia Verde,

Journal: JCAP01(2018)004

url: http://arxiv.org/pdf/1709.07467v2.pdf

Abstract: The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones.

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Understanding caustic crossings in giant arcs: characteristic scales,   event rates, and constraints on compact dark matter

Published Paper #: 538

Authors:, Masamune Oguri, Jose M. Diego, Nick Kaiser, Patrick L. Kelly, Tom Broadhurst,

Journal: Phys. Rev. D 97, 023518 (2018)

url: http://arxiv.org/pdf/1710.00148v2.pdf

Abstract: The recent discovery of fast transient events near critical curves of massive galaxy clusters, which are interpreted as highly magnified individual stars in giant arcs due to caustic crossing, opens up the possibility of using such microlensing events to constrain a range of dark matter models such as primordial black holes and scalar field dark matter. Based on a simple analytic model, we study lensing properties of a point mass lens embedded in a high magnification region, and derive the dependence of the peak brightness, microlensing time scales, and event rates on the mass of the point mass lens as well as the radius of a source star that is magnified. We find that the lens mass and source radius of the first event MACS J1149 Lensed Star 1 (LS1) are constrained, with the lens mass range of $0.1~M_\odot \lesssim M \lesssim 4\times 10^3M_\odot$ and the source radius range of $40~R_\odot \lesssim R \lesssim 260~R_\odot$. In the most plausible case with $M\approx 0.3~M_\odot$ and $R\approx 180~R_\odot$, the source star should have been magnified by a factor of $\approx 4300$ at the peak. The derived lens properties are fully consistent with the interpretation that MACS J1149 LS1 is a microlensing event produced by a star that contributes to the intra-cluster light. We argue that compact dark matter models with high fractional mass densities for the mass range $10^{-5}M_\odot \lesssim M\lesssim 10^2M_\odot$ are inconsistent with the observation of MACS J1149 LS1 because such models predict too low magnifications. Our work demonstrates a potential use of caustic crossing events in giant arcs to constrain compact dark matter.

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The merger rate of primordial-black-hole binaries

Published Paper #: 537

Authors:, Yacine Ali-Haïmoud, Ely D. Kovetz, Marc Kamionkowski,

Journal: Phys. Rev. D 96, 123523 (2017)

url: http://arxiv.org/pdf/1709.06576v2.pdf

Abstract: Primordial black holes (PBHs) have long been a candidate for the elusive dark matter (DM), and remain poorly constrained in the ~20-100 Msun mass range. PBH binaries were recently suggested as the possible source of LIGO's first detections. In this paper, we thoroughly revisit existing estimates of the merger rate of PBH binaries. We compute the probability distribution of orbital parameters for PBH binaries formed in the early Universe, accounting for tidal torquing by all other PBHs, as well as standard large-scale adiabatic perturbations. We then check whether the orbital parameters of PBH binaries formed in the early Universe can be significantly affected between formation and merger. Our analytic estimates indicate that the tidal field of halos and interactions with other PBHs, as well as dynamical friction by unbound standard DM particles, do not do significant work on nor torque PBH binaries. We estimate the torque due to baryon accretion to be much weaker than previous calculations, albeit possibly large enough to significantly affect the eccentricity of typical PBH binaries. We also revisit the PBH-binary merger rate resulting from gravitational capture in present-day halos, accounting for Poisson fluctuations. If binaries formed in the early Universe survive to the present time, as suggested by our analytic estimates, they dominate the total PBH merger rate. Moreover, this merger rate would be orders of magnitude larger than LIGO's current upper limits if PBHs make a significant fraction of the dark matter. As a consequence, LIGO would constrain ~10-300 Msun PBHs to constitute no more than ~1% of the dark matter. To make this conclusion fully robust, though, numerical study of several complex astrophysical processes - such as the formation of the first PBH halos and how they may affect PBH binaries, as well as the accretion of gas onto an extremely eccentric binary - is needed.

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$\mathcal O(10) M_\odot$ primordial black holes and string axion dark   matter

Published Paper #: 536

Authors:, Keisuke Inomata, Masahiro Kawasaki, Kyohei Mukaida, Yuichiro Tada, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 96, 123527 (2017)

url: http://arxiv.org/pdf/1709.07865v2.pdf

Abstract: LIGO-Virgo collaboration has found black holes as heavy as $M \sim 30M_\odot$ through the detections of the gravitational waves emitted during their mergers. Primordial black holes (PBHs) produced by inflation could be an origin of such events. While it is tempting to presume that these PBHs constitute all Dark Matter (DM), there exists a number of constraints for PBHs with $\mathcal{O} (10) M_\odot$ which contradict with the idea of PBHs as all DM. Also, it is known that weakly interacting massive particle (WIMP) that is a common DM candidate is almost impossible to coexist with PBHs. These observations motivate us to pursue another candidate of DM. In this paper, we assume that the string axion solving the strong CP problem makes up all DM, and discuss the coexistence of string axion DM and inflationary PBHs for LIGO events.

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Primordial black hole dark matter from single field inflation

Published Paper #: 535

Authors:, Guillermo Ballesteros, Marco Taoso,

Journal: Phys. Rev. D 97, 023501 (2018)

url: http://arxiv.org/pdf/1709.05565v2.pdf

Abstract: We propose a model of inflation capable of generating a population of light black holes (about $10^{-16}$ - $10^{-14}$ solar masses) that might account for a significant fraction of the dark matter in the Universe. The effective potential of the model features an approximate inflection point arising from two-loop order logarithmic corrections in well-motivated and perturbative particle physics examples. This feature decelerates the inflaton before the end of inflation, enhancing the primordial spectrum of scalar fluctuations and triggering efficient black hole production with a peaked mass distribution. At larger field values, inflation occurs thanks to a generic small coupling between the inflaton and the curvature of spacetime. We compute accurately the peak mass and abundance of the primordial black holes using the Press-Schechter and Mukhanov-Sasaki formalisms, showing that the slow-roll approximation fails to reproduce the correct results by orders of magnitude. We study as well a qualitatively similar implementation of the idea, where the approximate inflection point is due to competing terms in a generic polynomial potential. In both models, requiring a significant part of the dark matter abundance to be in the form of black holes implies a small blue scalar tilt with a sizable negative running and a tensor spectrum that may be detected by the next-generation probes of the cosmic microwave background. We also comment on previous works on the topic.

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Primordial black holes from single field models of inflation

Published Paper #: 534

Authors:, Juan Garcia-Bellido, Ester Ruiz Morales,

Journal: Physics Dark Universe 18 (2017) 47-54

url: http://arxiv.org/pdf/1702.03901v6.pdf

Abstract: Primordial black holes (PBH) have been shown to arise from high peaks in the matter power spectra of multi-field models of inflation. Here we show, with a simple toy model, that it is also possible to generate a peak in the curvature power spectrum of single-field inflation. We assume that the effective dynamics of the inflaton field presents a near-inflection point which slows down the field right before the end of inflation and gives rise to a prominent spike in the fluctuation power spectrum at scales much smaller than those probed by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) observations. This peak will give rise, upon reentry during the radiation era, to PBH via gravitational collapse. The mass and abundance of these PBH is such that they could constitute the totality of the Dark Matter today. We satisfy all CMB and LSS constraints and predict a very broad range of PBH masses. Some of these PBH are light enough that they will evaporate before structure formation, leaving behind a large curvature fluctuation on small scales. This broad mass distribution of PBH as Dark Matter will be tested in the future by AdvLIGO and LISA interferometers.

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Modified hoop conjecture in expanding spacetimes and primordial black   hole production in FRW universe

Published Paper #: 533

Authors:, Anshul Saini, Dejan Stojkovic,

Journal: JCAP05(2018)071

url: http://arxiv.org/pdf/1711.06732v1.pdf

Abstract: According to a variant of the hoop conjecture, if we localize two particles within the Schwarzschild radius corresponding to their center of mass energy, then a black hole will form. Despite a large body of work on the formation of primordial black holes, so far this conjecture has not been generalized to expanding spacetimes. We derive a formula which gives the distance within which two particles must be localized to give a black hole, and which crucially depends on the expansion rate of the background space. In the limit of a very slow expansion, we recover the flat spacetime case. In the opposite limit of the large expansion rate when the inverse Hubble radius is smaller than the Schwarzschild radius of a "would be" black hole, the new critical distance between two particles that can make a black hole becomes equal to the particle horizon, which is just a requirement that the particles are in a causal contact. This behavior also nicely illustrates why the Big Bang singularity is not a black hole. We then use our formula to calculate the number density, energy density and production rate of black holes produced in collisions of particles. We find that though black holes might be numerous at high temperatures, they never dominate over the background radiation below the Planck temperature.

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CMB bounds on disk-accreting massive Primordial Black Holes

Published Paper #: 532

Authors:, Vivian Poulin, Pasquale D. Serpico, Francesca Calore, Sebastien Clesse, Kazunori Kohri,

Journal: Phys. Rev. D 96, 083524 (2017)

url: http://arxiv.org/pdf/1707.04206v2.pdf

Abstract: Stellar-mass Primordial Black Holes (PBH) have been recently reconsidered as a Dark Matter (DM) candidate, after the aLIGO discovery of several binary BH mergers with masses of tens of $M_\odot$. Matter accretion on such massive objects leads to the emission of high-energy photons, capable of altering the ionization and thermal history of the universe. This in turn affects the statistical properties of the cosmic microwave background (CMB) anisotropies. Previous analyses have assumed spherical accretion. We argue that this approximation likely breaks down and that an accretion disk should form in the dark ages. Using the most up-to-date tools to compute the energy deposition in the medium, we derive constraints on the fraction of DM in PBH. Provided that disks form early on, even under conservative assumptions for accretion, these constraints exclude a monochromatic distribution of PBH with masses above $\sim 2\, M_\odot$ as the dominant form of DM. The bound on the median PBH mass gets more stringent if a broad, log-normal mass function is considered. A deepened understanding of non-linear clustering properties and BH accretion disk physics would permit an improved treatment and possibly lead to more stringent constraints.

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Signatures of Compact Halos of Sterile-Neutrino Dark Matter

Published Paper #: 531

Authors:, Florian Kuhnel, Tommy Ohlsson,

Journal: Phys. Rev. D 96, 103020 (2017)

url: http://arxiv.org/pdf/1707.04493v2.pdf

Abstract: We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultra-compact mini-halos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with X-ray and gamma-ray telescopes might be well possible. In fact, for energies above $10\,{\rm TeV}$, the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.

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Critical point in the phase diagram of primordial quark-gluon matter   from black hole physics

Published Paper #: 530

Authors:, Renato Critelli, Jorge Noronha, Jacquelyn Noronha-Hostler, Israel Portillo, Claudia Ratti, Romulo Rougemont,

Journal: Phys. Rev. D 96, 096026 (2017)

url: http://arxiv.org/pdf/1706.00455v3.pdf

Abstract: Strongly interacting matter undergoes a crossover phase transition at high temperatures $T\sim 10^{12}$ K and zero net-baryon density. A fundamental question in the theory of strong interactions, Quantum Chromodynamics (QCD), is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations. Here we use the holographic gauge/gravity correspondence to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes. This approach quantitatively reproduces ab initio results for the lowest order moments of the baryon fluctuations and makes predictions for the higher order baryon susceptibilities and also for the location of the critical point, which is found to be within the reach of heavy ion collision experiments.

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Gravitational wave bursts from Primordial Black Hole hyperbolic   encounters

Published Paper #: 529

Authors:, Juan Garcia-Bellido, Savvas Nesseris,

Journal: Phys.Dark Univ., 18 (2017) 123-126

url: http://arxiv.org/pdf/1706.02111v2.pdf

Abstract: We propose that Gravitational Wave (GW) bursts with millisecond durations can be explained by the GW emission from the hyperbolic encounters of Primordial Black Holes in dense clusters. These bursts are single events, with the bulk of the released energy happening during the closest approach, and emitted in frequencies within the AdvLIGO sensitivity range. We provide expressions for the shape of the GW emission in terms of the peak frequency and amplitude, and estimate the rates of these events for a variety of mass and velocity configurations. We study the regions of parameter space that will allow detection by both AdvLIGO and, in the future, LISA. We find for realistic configurations, with total mass $M\sim60\,M_\odot$, relative velocities $v\sim 0.01\,c$, and impact parameters $b\sim10^{-3}$ AU, for AdvLIGO an expected event rate is ${\cal O}(10)$ events/yr/Gpc$^3$ with millisecond durations. For LISA, the typical duration is in the range of minutes to hours and the event-rate is ${\cal O}(10^3)$ events/yr/Gpc$^3$ for both $10^3\,M_\odot$ IMBH and $10^6\,M_\odot$ SMBH encounters. We also study the distribution functions of eccentricities, peak frequencies and characteristic timescales that can be expected for a population of scattering PBH with a log-normal distribution in masses, different relative velocities and a flat prior on the impact parameter.

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Maximum redshift of gravitational wave merger events

Published Paper #: 528

Authors:, Savvas M. Koushiappas, Abraham Loeb,

Journal: Phys. Rev. Lett. 119, 221104 (2017)

url: http://arxiv.org/pdf/1708.07380v2.pdf

Abstract: Future generation of gravitational wave detectors will have the sensitivity to detect gravitational wave events at redshifts far beyond any detectable electromagnetic sources. We show that if the observed event rate is greater than one event per year at redshifts z > 40, then the probability distribution of primordial density fluctuations must be significantly non-Gaussian or the events originate from primordial black holes. The nature of the excess events can be determined from the redshift distribution of the merger rate.

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Cosmological implications of Primordial Black Holes

Published Paper #: 527

Authors:, José Luis Bernal, Nicola Bellomo, Alvise Raccanelli, Licia Verde,

Journal: JCAP10(2017)052

url: http://arxiv.org/pdf/1709.07465v2.pdf

Abstract: The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a $\sim 30 M_{\odot}$ binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observations, finding significant degeneracies, especially with the tilt of the primordial power spectrum and the sound horizon at radiation drag. However, these degeneracies can be greatly reduced with the inclusion of small scale polarization data. We also explore if PBHs as dark matter in simple extensions of the standard $\Lambda$CDM cosmological model induces extra degeneracies, especially between the additional parameters and the PBH's ones. Finally, we present cosmic microwave background constraints on the fraction of dark matter in PBHs, not only for monochromatic PBH mass distributions but also for popular extended mass distributions. Our results show that extended mass distribution's constraints are tighter, but also that a considerable amount of constraining power comes from the high-$\ell$ polarization data. Moreover, we constrain the shape of such mass distributions in terms of the correspondent constraints on the PBH mass fraction.

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Probing Primordial-Black-Hole Dark Matter with Gravitational Waves

Published Paper #: 526

Authors:, Ely D. Kovetz,

Journal: Phys. Rev. Lett. 119, 131301 (2017)

url: http://arxiv.org/pdf/1705.09182v2.pdf

Abstract: Primordial black holes (PBHs) have long been suggested as a candidate for making up some or all of the dark matter in the Universe. Most of the theoretically possible mass range for PBH dark matter has been ruled out with various null observations of expected signatures of their interaction with standard astrophysical objects. However, current constraints are significantly less robust in the 20 M_sun < M_PBH < 100 M_sun mass window, which has received much attention recently, following the detection of merging black holes with estimated masses of ~30 M_sun by LIGO and the suggestion that these could be black holes formed in the early Universe. We consider the potential of advanced LIGO (aLIGO) operating at design sensitivity to probe this mass range by looking for peaks in the mass spectrum of detected events. To quantify the background, which is due to black holes that are formed from dying stars, we model the shape of the stellar-black-hole mass function and calibrate its amplitude to match the O1 results. Adopting very conservative assumptions about the PBH and stellar-black-hole merger rates, we show that ~5 years of aLIGO data can be used to detect a contribution of >20 M_sun PBHs to dark matter down to f_PBH<0.5 at >99.9% confidence level. Combined with other probes that already suggest tension with f_PBH=1, the obtainable independent limits from aLIGO will thus enable a firm test of the scenario that PBHs make up all of dark matter.

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Using LISA-like Gravitational Wave Detectors to Search for Primordial   Black Holes

Published Paper #: 525

Authors:, Huai-Ke Guo, Jing Shu, Yue Zhao,

Journal: Phys. Rev. D 99, 023001 (2019)

url: http://arxiv.org/pdf/1709.03500v1.pdf

Abstract: Primordial black hole (PBH), which can be naturally produced in the early universe, remains a promising dark matter candidate . It can merge with a supermassive black hole (SMBH) in the center of a galaxy and generate gravitational wave (GW) signals in the favored frequency region of LISA-like experiments. In this work, we initiate the study on the event rate calculation for such extreme mass ratio inspirals (EMRI). Including the sensitivities of various proposed GW detectors, we find that such experiments offer a novel and outstanding tool to test the scenario where PBH constitutes (fraction of) dark matter. The PBH energy density fraction of DM ($f_\text{PBH}$) could potentially be explored as small as $10^{-3} \sim 10^{-4}$. Further, LISA has the capability to search for PBH mass upto $10^{-2} \sim 10^{-1} M_\odot$. Other proposed GW experiments can probe lower PBH mass regime.

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Primordial Black Holes and Slow-Roll Violation

Published Paper #: 524

Authors:, Hayato Motohashi, Wayne Hu,

Journal: Phys. Rev. D 96, 063503 (2017)

url: http://arxiv.org/pdf/1706.06784v2.pdf

Abstract: For primordial black holes (PBH) to be the dark matter in single-field inflation, the slow-roll approximation must be violated by at least ${\cal O}(1)$ in order to enhance the curvature power spectrum within the required number of efolds between CMB scales and PBH mass scales. Power spectrum predictions which rely on the inflaton remaining on the slow-roll attractor can fail dramatically leading to qualitatively incorrect conclusions in models like an inflection potential and misestimate the mass scale in a running mass model. We show that an optimized temporal evaluation of the Hubble slow-roll parameters to second order remains a good description for a wide range of PBH formation models where up to a $10^7$ amplification of power occurs in $10$ efolds or more.

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Primordial black holes from inflaton and spectator field perturbations   in a matter-dominated era

Published Paper #: 523

Authors:, Bernard Carr, Tommi Tenkanen, Ville Vaskonen,

Journal: Phys. Rev. D 96, 063507 (2017)

url: http://arxiv.org/pdf/1706.03746v2.pdf

Abstract: We study production of primordial black holes (PBHs) during an early matter-dominated phase. As a source of perturbations, we consider either the inflaton field with a running spectral index or a spectator field that has a blue spectrum and thus provides a significant contribution to the PBH production at small scales. First, we identify the region of the parameter space where a significant fraction of the observed dark matter can be produced, taking into account all current PBH constraints. Then, we present constraints on the amplitude and spectral index of the spectator field as a function of the reheating temperature. We also derive constraints on the running of the inflaton spectral index, ${\rm d}n/{\rm d}{\rm ln}k \lesssim -0.002$, which are comparable to those from the Planck satellite for a scenario where the spectator field is absent.

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Search for Primordial Black Hole Evaporation with VERITAS

Published Paper #: 522

Authors:, Simon Archambault,

Journal: PoS(ICRC2017)691

url: http://arxiv.org/pdf/1709.00307v1.pdf

Abstract: Primordial black holes are black holes that may have formed from density fluctuations in the early universe. It has been theorized that black holes slowly evaporate. If primordial black holes of initial mass of $10^{14}$g were formed, their evaporation would end in this epoch, in a bright burst of very-high-energy gamma rays. A Cherenkov telescope experiment like VERITAS can look for these primordial black hole bursts in its archival data, constraining the rate-density of their final evaporation. New analysis techniques and search methodologies were used and will be presented here, leading to new constraints on the rate-density evaporation of primordial black holes, using 750 hours of archival VERITAS data.

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Gravitational waves from primordial black holes collisions in binary   systems

Published Paper #: 521

Authors:, Yu. N. Eroshenko,

Journal: J. Phys.: Conf. Ser. 1051, 012010 (2018)

url: http://arxiv.org/pdf/1604.04932v3.pdf

Abstract: It was shown by (Nakamura et al. 1997), (Ioka et al. 1998), and (Sasaki et al. 2016) that primordial black holes (PBHs) binaries can form effectively at the cosmological stage of radiation dominance, and the merge of the PBHs in pairs can explain the gravitational wave burst GW150914. In this paper, the model is re-examined by considering the effect of inflationary dark matter density perturbations which produce additional tidal forces. As a result, the merge rate of PBHs binaries and the corresponding rate of the gravitational bursts are suppressed by the factor $\sim1.5-2$ in comparison with previous calculations. This rate matches the LIGO data if the PBHs constitute the $f\sim5\times10^{-4}-5\times10^{-3}$ fraction of dark matter.

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Collapse threshold for a cosmological Klein Gordon field

Published Paper #: 520

Authors:, Juan Carlos Hidalgo, Josue De-Santiago, Gabriel German, Nandinii Barbosa-Cendejas, Waldemar Ruiz-Luna,

Journal: Phys. Rev. D 96, 063504 (2017)

url: http://arxiv.org/pdf/1705.02308v2.pdf

Abstract: Oscillating scalar fields are useful to model a variety of matter components in the universe. One or more scalar fields participate in the reheating process after inflation, while at much lower energies scalar fields are robust dark matter candidates. Pertaining structure formation in these models, it is well known that inhomogeneities of the Klein-Gordon field are unstable above the characteristic De Broglie wavelength. In this paper we show that such instability implies the existence of a threshold amplitude for the collapse of primordial fluctuations. We use this threshold to correctly predict the cut--off scale of the matter power spectrum in the scalar field dark matter model. Furthermore, for a Klein-Gordon field during reheating we show that this same threshold allows for abundant production of structure (oscillons but not necessarily black holes). Looking at the production of Primordial Black Holes (PBHs) in this scenario we note that the sphericity condition yields a much lower probability of PBH formation at the end of inflation. Remarkably, even after meeting such stringent condition, we find that PBHs may be overproduced during reheating. We finally constrain the epochs at which an oscillating Klein-Gordon field could dominate the early universe.

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Primordial Black Holes and $r$-Process Nucleosynthesis

Published Paper #: 519

Authors:, George M. Fuller, Alexander Kusenko, Volodymyr Takhistov,

Journal: Phys. Rev. Lett. 119, 061101 (2017)

url: http://arxiv.org/pdf/1704.01129v2.pdf

Abstract: We show that some or all of the inventory of $r$-process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses ${10}^{-14}\,{\rm M}_\odot < {\rm M}_{\rm PBH} < {10}^{-8}\,{\rm M}_\odot$ make up a few percent or more of the dark matter. A PBH captured by a neutron star (NS) sinks to the center of the NS and consumes it from the inside. When this occurs in a rotating millisecond-period NS, the resulting spin-up ejects $\sim 0.1-0.5\,{\rm M}_{\odot}$ of relatively cold neutron-rich material. This ejection process and the accompanying decompression and decay of nuclear matter can produce electromagnetic transients, such as a kilonova-type afterglow and fast radio bursts. These transients are not accompanied by significant gravitational radiation or neutrinos, allowing such events to be differentiated from compact object mergers occurring within the distance sensitivity limits of gravitational wave observatories. The PBH-NS destruction scenario is consistent with pulsar and NS statistics, the dark matter content and spatial distributions in the Galaxy and Ultra Faint Dwarfs (UFD), as well as with the $r$-process content and evolution histories in these sites. Ejected matter is heated by beta decay, which leads to emission of positrons in an amount consistent with the observed 511-keV line from the Galactic Center.

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Planck stars: new sources in radio and gamma astronomy?

Published Paper #: 518

Authors:, Carlo Rovelli,

Journal: Nature Astronomy 1 (2017) 0065

url: http://arxiv.org/pdf/1708.01789v1.pdf

Abstract: A new phenomenon, recently studied in theoretical physics, may have considerable interest for astronomers: the explosive decay of old primordial black holes via quantum tunnelling. Models predict radio and gamma bursts with a characteristic frequency-distance relation making them identifiable. Their detection would be of major theoretical importance.

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Astrophysical uncertainties on stellar microlensing constraints on   multi-Solar mass primordial black hole dark matter

Published Paper #: 517

Authors:, Anne M Green,

Journal: Phys. Rev. D 96, 043020 (2017)

url: http://arxiv.org/pdf/1705.10818v2.pdf

Abstract: There has recently been interest in multi-Solar mass Primordial Black Holes (PBHs) as a dark matter (DM) candidate. There are various microlensing, dynamical and accretion constraints on the abundance of PBHs in this mass range. Taken at face value these constraints exclude multi-Solar mass PBHs making up all of the DM for both delta-function and extended mass functions. However the stellar microlensing event rate depends on the density and velocity distribution of the compact objects along the line of sight to the Magellanic Clouds. We study the dependence of the constraints on the local dark matter density and circular speed and also consider models where the velocity distribution varies with radius. We find that the largest mass constrained by stellar microlensing can vary by an order of magnitude. In particular the constraints are significantly weakened if the velocity dispersion of the compact objects is reduced. The change is not sufficiently large to remove the tension between the stellar microlensing and dynamical constraints. However this demonstrates that it is crucial to take into account astrophysical uncertainties when calculating and comparing constraints. We also confirm the recent finding that the tension between the constraints is in fact increased for realistic, finite width mass functions.

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PBH dark matter from axion inflation

Published Paper #: 516

Authors:, Valerie Domcke, Francesco Muia, Mauro Pieroni, Lukas T. Witkowski,

Journal: JCAP 07 (2017) 048

url: http://arxiv.org/pdf/1704.03464v2.pdf

Abstract: Protected by an approximate shift symmetry, axions are well motivated candidates for driving cosmic inflation. Their generic coupling to the Chern-Simons term of any gauge theory gives rise to a wide range of potentially observable signatures, including equilateral non-Gaussianites in the CMB, chiral gravitational waves in the range of direct gravitational wave detectors and primordial black holes (PBHs). In this paper we revisit these predictions for axion inflation models non-minimally coupled to gravity. Contrary to the case of minimally coupled models which typically predict scale-invariant mass distributions for the generated PBHs at small scales, we demonstrate how broadly peaked PBH spectra naturally arises in this setup. For specific parameter values, all of dark matter can be accounted for by PBHs.

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Disentangling the potential dark matter origin of LIGO's black holes

Published Paper #: 515

Authors:, Ryan Magee, Chad Hanna,

Journal: The Astrophysical Journal Letters, Volume 845, Number 2 (2017)

url: http://arxiv.org/pdf/1706.04947v3.pdf

Abstract: The nature of dark matter remains one of the biggest open questions in physics. Intriguingly, it has been suggested that dark matter may be explained by another recently observed phenomenon: the detection of gravitational waves by LIGO. LIGO's detection of gravitational waves from merging stellar mass black holes renewed attention toward the possibility that dark matter consists solely of black holes created in the very early universe and that these primordial black holes are what LIGO is presently observing. Subsequent work on this topic has ruled out the possibility that dark matter could consist solely of black holes similar to those that LIGO has detected with masses above 10 solar masses. However, LIGO's connection to dark matter remains an open question and in this work we consider a distribution of primordial black holes that accounts for all of the dark matter, is consistent with LIGO's observations arising from primordial black hole binaries, and resolves tension in previous surveys of microlensing events in the Milky Way halo. The primordial black hole mass distribution that we consider offers an important prediction--LIGO may detect black holes smaller than have ever been observed with ~1% of the black holes it detects having a mass less than the mass of our Sun. Approximately one year of operating advanced LIGO at design sensitivity should be adequate to begin to see a hint of a primordial black hole mass distribution. Detecting primordial black hole binaries below a solar mass will be readily distinguishable from other known compact binary systems, thereby providing an unambiguous observational window for advanced LIGO to pin down the nature of dark matter.

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Detecting Sub-lunar Mass Compact Objects toward the Local Group Galaxies

Published Paper #: 514

Authors:, Kaiki Taro Inoue,

Journal: New Astronomy, 58, pp. 47-52 (Jan. 2018)

url: http://arxiv.org/pdf/1609.04520v2.pdf

Abstract: By monitoring a large number of stars in the Local Group galaxies, we can detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the Milky Way halo. In contarst to microlensing by stellar-mass objects, the finite-source size effect becomes important and the lensing time duration becomes shorter ($\sim 10^{1-4}\,\textrm{s}$). Using stars with $V<26$ in M33 as sources, for one-night observation, we would be able to detect $10^{3-4}$ nanolensing events caused by SULCOs in the Milky Way halo with a mass of $10^{-9}M_{\odot}$ to $10^{-7}M_{\odot}$ for sources with S/N$>5$ if SULCOs constitute all the dark matter components. Moreover, we expect $10^{1-2}$ events in which bright blue stars with S/N$>100$ are weakly amplified due to lensing by SULCOs with a mass range of $10^{-11}M_{\odot}$ to $10^{-9}M_{\odot}$. Thus the method would open a new window on SULCOs in the Milky Way halo that would otherwise not be observable.

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Primordial black holes from supersymmetry in the early universe

Published Paper #: 513

Authors:, Eric Cotner, Alexander Kusenko,

Journal: Phys. Rev. Lett. 119, 031103 (2017)

url: http://arxiv.org/pdf/1612.02529v3.pdf

Abstract: Supersymmetric extensions of the standard model generically predict that in the early universe a scalar condensate can form and fragment into Q-balls before decaying. If the Q-balls dominate the energy density for some period of time, the relatively large fluctuations in their number density can lead to formation of primordial black holes (PBH). Other scalar fields, unrelated to supersymmetry, can play a similar role. For a general charged scalar field, this robust mechanism can generate black holes over the entire mass range allowed by observational constraints, with a sufficient abundance to account for all dark matter in some parameter ranges. In the case of supersymmetry the mass range is limited from above by $10^{23}$g. We also comment on the role that topological defects can play for PBH formation in a similar fashion.

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Searching for Primordial Black Holes in the radio and X-ray sky

Published Paper #: 512

Authors:, Daniele Gaggero, Gianfranco Bertone, Francesca Calore, Riley M. T. Connors, Mark Lovell, Sera Markoff, Emma Storm,

Journal: Phys. Rev. Lett. 118, 241101 (2017)

url: http://arxiv.org/pdf/1612.00457v2.pdf

Abstract: We model the accretion of gas onto a population of massive primordial black holes in the Milky Way, and compare the predicted radio and X-ray emission with observational data. We show that under conservative assumptions on the accretion process, the possibility that ${\cal O}(10) \, M_\odot$ primordial black holes can account for all of the dark matter in the Milky Way is excluded at $5\sigma$ by a comparison with a VLA radio catalog at $1.4$ GHz, and at $\simeq 40\sigma$ by a comparison with a Chandra X-ray catalog ($0.5 - 8$ keV). We argue that this method can be used to identify such a population of primordial black holes with more sensitive future radio and X-ray surveys.

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Primordial black holes from scalar field evolution in the early universe

Published Paper #: 511

Authors:, Eric Cotner, Alexander Kusenko,

Journal: Phys. Rev. D 96, 103002 (2017)

url: http://arxiv.org/pdf/1706.09003v1.pdf

Abstract: Scalar condensates with large expectation values can form in the early universe, for example, in theories with supersymmetry. The condensate can undergo fragmentation into Q-balls before decaying. If the Q-balls dominate the energy density for some period of time, statistical fluctuations in their number density can lead to formation of primordial black holes (PBH). In the case of supersymmetry the mass range is limited from above by $10^{23}$g. For a general charged scalar field, this robust mechanism can generate black holes over a much broader mass range, including the black holes with masses of 1-100 solar masses, which is relevant for LIGO observations of gravitational waves. Topological defects can lead to formation of PBH in a similar fashion.

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Spin Distribution of Primordial Black Holes

Published Paper #: 510

Authors:, Takeshi Chiba, Shuichiro Yokoyama,

Journal: PTEP 2017 8, 083E01 (2017)

url: http://arxiv.org/pdf/1704.06573v2.pdf

Abstract: We estimate the spin distribution of primordial black holes based on the recent study of the critical phenomena in the gravitational collapse of a rotating radiation fluid. We find that primordial black holes are mostly slowly rotating.

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MHz Gravitational Wave Constraints with Decameter Michelson   Interferometers

Published Paper #: 509

Authors:, Aaron S. Chou, Richard Gustafson, Craig Hogan, Brittany Kamai, Ohkyung Kwon, Robert Lanza, Shane L. Larson, Lee McCuller, Stephan S. Meyer, Jonathan Richardson, Chris Stoughton, Raymond Tomlin, Rainer Weiss,

Journal: Phys. Rev. D 95, 063002 (2017)

url: http://arxiv.org/pdf/1611.05560v2.pdf

Abstract: A new detector, the Fermilab Holometer, consists of separate yet identical 39-meter Michelson interferometers. Strain sensitivity achieved is better than $10^{-21} /{\sqrt{\rm{Hz}}}$ between 1 to 13 MHz from a 130-hr dataset. This measurement exceeds the sensitivity and frequency range made from previous high frequency gravitational wave experiments by many orders of magnitude. Constraints are placed on a stochastic background at 382 Hz resolution. The 3$\sigma$ upper limit on $\Omega_{\rm{GW}}$, the gravitational wave energy density normalized to the closure density, ranges from $5.6 \times 10^{12}$ at 1 MHz to $8.4 \times 10^{15}$ at 13 MHz. Another result from the same dataset is a search for nearby primordial black hole binaries (PBHB). There are no detectable monochromatic PBHBs in the mass range $0.83$ - $3.5 \times 10^{21}$g between the earth and the moon. Projections for a chirp search with the same dataset increases the mass range to $0.59 - 2.5 \times 10^{25}$g and distances out to Jupiter. This result presents a new method for placing limits on a poorly constrained mass range of primordial black holes. Additionally, solar system searches for PBHBs place limits on their contribution to the total dark matter fraction.

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The primordial environment of supermassive black holes (II): deep Y and   J band images around the z=6.3 quasar SDSS J1030+0524

Published Paper #: 508

Authors:, B. Balmaverde, R. Gilli, M. Mignoli, M. Bolzonella, M. Brusa, N. Cappelluti, A. Comastri, E. Sani, E. Vanzella, C. Vignali, F. Vito, G. Zamorani,

Journal: A&A 606, A23 (2017)

url: http://arxiv.org/pdf/1706.02317v1.pdf

Abstract: Many cosmological studies predict that early supermassive black holes (SMBHs) can only form in the most massive dark matter halos embedded within large scale structures marked by galaxy over-densities that may extend up to 10 physical Mpc. This scenario, however, has not been confirmed observationally, as the search for galaxy over-densities around high-z quasars has returned conflicting results. The field around the z=6.28 quasar SDSSJ1030+0524 (J1030) is unique for multi-band coverage and represents an excellent data legacy for studying the environment around a primordial SMBH. In this paper we present wide-area (25x25 arcmin), Y- and J-band imaging of the J1030 field obtained with the near infrared camera WIRCam at the Canada-France-Hawaii Telescope (CFHT). We built source catalogues in the Y- and J-band, and matched those with our photometric catalogue in the r, z, i bands presented in Morselli et al. (2014). We used these new infrared data together with H and K and Spitzer/IRAC data to refine our selection of Lyman Break Galaxies (LBGs), extending our selection criteria to galaxies in the range 25.2<zAB<25.7. We selected 21 robust high-z candidates in the J1030 field with photometric redshift around 6 and colors i-z>=1.3. We found a significant asymmetry in the distribution of the high-z galaxies in J1030, supporting the existence of a coherent large-scale structure around the quasar. We compared our results with those of Bowler et al. (2015), who adopted similar LBGs selection criteria, and estimated an over-density of galaxies in the field of delta = 2.4, which is significant at >4 sigma. The over-density value and its significance are higher than those found in Morselli et al. (2014), and we interpret this as evidence of an improved LBG selection.

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Inflationary primordial black holes for the LIGO gravitational wave   events and pulsar timing array experiments

Published Paper #: 507

Authors:, Keisuke Inomata, Masahiro Kawasaki, Kyohei Mukaida, Yuichiro Tada, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 95, 123510 (2017)

url: http://arxiv.org/pdf/1611.06130v2.pdf

Abstract: Primordial black holes (PBHs) are one of the candidates to explain the gravitational wave (GW) signals observed by the LIGO detectors. Among several phenomena in the early Universe, cosmic inflation is a major example to generate PBHs from large primordial density perturbations. In this paper, we discuss the possibility to interpret the observed GW events as mergers of PBHs which are produced by cosmic inflation. The primordial curvature perturbation should be large enough to produce a sizable amount of PBHs and thus we have several other probes to test this scenario. We point out that the current pulsar timing array (PTA) experiments already put severe constraints on GWs generated via the second-order effects, and that the observation of the cosmic microwave background (CMB) puts severe restriction on its $\mu$ distortion. In particular, it is found that the scalar power spectrum should have a very sharp peak at $k \sim 10^{6}$ Mpc$^{-1}$ to fulfill the required abundance of PBHs while evading constraints from the PTA experiments together with the $\mu$ distortion. We propose a mechanism which can realize such a sharp peak. In the future, simple inflation models that generate PBHs via almost Gaussian fluctuations could be probed/excluded.

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Cosmological evolution of primordial black holes

Published Paper #: 506

Authors:, Jared R. Rice, Bing Zhang,

Journal: 2017, Journal of High Energy Astrophysics,13, 22-31

url: http://arxiv.org/pdf/1702.08069v2.pdf

Abstract: The cosmological evolution of primordial black holes (PBHs) is considered. A comprehensive view of the accretion and evaporation histories of PBHs across the entire cosmic history is presented, with focus on the critical mass holes. The critical mass of a PBH for current era evaporation is $M_{cr}\sim 5.1\times10^{14}$ g. Across cosmic time such a black hole will not accrete radiation or matter in sufficient quantity to hasten the inevitable evaporation, if the black hole remains within an average volume of the universe. The accretion rate onto PBHs is most sensitive to the mass of the hole, the sound speed in the cosmological fluid, and the energy density of the accreted components. It is not easy for a PBH to accrete the average cosmological fluid to reach $30M_\odot$ by $z\sim0.1$, the approximate mass and redshift of the merging BHs that were the sources of the gravitational wave events GW150914 and GW151226. A PBH located in an overdense region can undergo enhanced accretion leading to the possibility of growing by many orders of magnitude across cosmic history. Thus, two merging PBHs are a plausible source for the observed gravitational wave events. However, it is difficult for isolated PBHs to grow to supermassive black holes (SMBHs) at high redshift with masses large enough to fit observational constraints.

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Inflationary Primordial Black Holes as All Dark Matter

Published Paper #: 505

Authors:, Keisuke Inomata, Masahiro Kawasaki, Kyohei Mukaida, Yuichiro Tada, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 96, 043504 (2017)

url: http://arxiv.org/pdf/1701.02544v3.pdf

Abstract: Following a new microlensing constraint on primordial black holes (PBHs) with $\sim10^{20}$--$10^{28}\,\mathrm{g}$~[1], we revisit the idea of PBH as all Dark Matter (DM). We have shown that the updated observational constraints suggest the viable mass function for PBHs as all DM to have a peak at $\simeq 10^{20}\,\mathrm{g}$ with a small width $\sigma \lesssim 0.1$, by imposing observational constraints on an extended mass function in a proper way. We have also provided an inflation model that successfully generates PBHs as all DM fulfilling this requirement.

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Tracing Primordial Black Holes in Nonsingular Bouncing Cosmology

Published Paper #: 504

Authors:, Jie-Wen Chen, Junyu Liu, Hao-Lan Xu, Yi-Fu Cai,

Journal: Physics Letters B 769 (2017) 561

url: http://arxiv.org/pdf/1609.02571v3.pdf

Abstract: We in this paper investigate the formation and evolution of primordial black holes (PBHs) in nonsingular bouncing cosmologies. We discuss the formation of PBH in the contracting phase and calculate the PBH abundance as a function of the sound speed and Hubble parameter. Afterwards, by taking into account the subsequent PBH evolution during the bouncing phase, we derive the density of PBHs and their Hawking radiation. Our analysis shows that nonsingular bounce models can be constrained from the backreaction of PBHs.

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Inflationary theory and pulsar timing investigations of primordial black   holes and gravitational waves

Published Paper #: 503

Authors:, Nicholas Orlofsky, Aaron Pierce, James D. Wells,

Journal: Phys. Rev. D 95, 063518 (2017)

url: http://arxiv.org/pdf/1612.05279v2.pdf

Abstract: The gravitational waves measured at LIGO are presumed here to come from merging primordial black holes. We ask how these primordial black holes could arise through inflationary models while not conflicting with current experiments. Among the approaches that work, we investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays. We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future. The models that are most strongly constrained are those with a relatively broad primordial power spectrum.

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Primordial Black Holes as Dark Matter

Published Paper #: 502

Authors:, Bernard Carr, Florian Kuhnel, Marit Sandstad,

Journal: Phys. Rev. D 94, 083504 (2016)

url: http://arxiv.org/pdf/1607.06077v4.pdf

Abstract: The possibility that the dark matter comprises primordial black holes (PBHs) is considered, with particular emphasis on the currently allowed mass windows at $10^{16}$ - $10^{17}\,$g, $10^{20}$ - $10^{24}\,$g and $1$ - $10^{3}\,M_{\odot}$. The Planck mass relics of smaller evaporating PBHs are also considered. All relevant constraints (lensing, dynamical, large-scale structure and accretion) are reviewed and various effects necessary for a precise calculation of the PBH abundance (non-Gaussianity, non-sphericity, critical collapse and merging) are accounted for. It is difficult to put all the dark matter in PBHs if their mass function is monochromatic but this is still possible if the mass function is extended, as expected in many scenarios. A novel procedure for confronting observational constraints with an extended PBH mass spectrum is therefore introduced. This applies for arbitrary constraints and a wide range of PBH formation models, and allows us to identify which model-independent conclusions can be drawn from constraints over all mass ranges. We focus particularly on PBHs generated by inflation, pointing out which effects in the formation process influence the mapping from the inflationary power spectrum to the PBH mass function. We then apply our scheme to two specific inflationary models in which PBHs provide the dark matter. The possibility that the dark matter is in intermediate-mass PBHs of $1$ - $10^{3}\,M_{\odot}$ is of special interest in view of the recent detection of black-hole mergers by LIGO. The possibility of Planck relics is also intriguing but virtually untestable.

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Gravitational Waves from Primordial Black Holes and New Weak Scale   Phenomena

Published Paper #: 501

Authors:, Hooman Davoudiasl, Pier Paolo Giardino,

Journal: Phys.Lett. B768 (2017) 198-202

url: http://arxiv.org/pdf/1609.00907v3.pdf

Abstract: We entertain the possibility that primordialblack holes of mass $\sim (10^{26}$--$10^{29})$~g, with Schwarzschild radii of $\mathcal{O}{\text{cm}}$, constitute $\sim 10\%$ or more of cosmic dark matter, as allowed by various constraints. These black holes would typically originate from cosmological eras corresponding to temperatures $\mathcal{O}{10-100}$~GeV, and may be associated with first order phase transitions in the visible or hidden sectors. In case these small primordial black holes get captured in orbits around neutron stars or astrophysical black holes in our galactic neighborhood, gravitational waves from the resulting "David and Goliath (D\&G)" binaries could be detectable at Advanced LIGO or Advanced Virgo for hours or more, possibly over distances of $\mathcal{O}{10}$~Mpc encompassing the Local Supercluster of galaxies. The proposed Einstein Telescope would further expand the reach for these signals. A positive signal could be further corroborated by the discovery of new particles in the $\mathcal{O}{10-100}$~GeV mass range, and potentially also the detection of long wavelength gravitational waves originating from the first order phase transition era.

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Digging deeper: Observing primordial gravitational waves below the   binary black hole produced stochastic background

Published Paper #: 500

Authors:, T. Regimbau, M. Evans, N. Christensen, E. Katsavounidis, B. Sathyaprakash, S. Vitale,

Journal: Phys. Rev. Lett. 118, 151105 (2017)

url: http://arxiv.org/pdf/1611.08943v2.pdf

Abstract: The merger rate of black hole binaries inferred from the detections in the first Advanced LIGO science run, implies that a stochastic background produced by a cosmological population of mergers will likely mask the primordial gravitational-wave background. Here we demonstrate that the next generation of ground-based detectors, such as the Einstein Telescope and Cosmic Explorer, will be able to observe binary black hole mergers throughout the universe with sufficient efficiency that the confusion background can potentially be subtracted to observe the primordial background at the level of $\Omega_{\mathrm{GW}} \simeq 10^{-13}$ after five years of observation.

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Enhanced direct collapse due to Lyman alpha feedback

Published Paper #: 499

Authors:, Jarrett L. Johnson, Mark Dijkstra,

Journal: A&A 601, A138 (2017)

url: http://arxiv.org/pdf/1611.00780v2.pdf

Abstract: We assess the impact of trapped Lyman alpha cooling radiation on the formation of direct collapse black holes (DCBHs). We apply a one-zone chemical and thermal evolution model, accounting for the photodetachment of H- ions, precursors to the key coolant H2, by Lyman alpha photons produced during the collapse of a cloud of primordial gas in an atomic cooling halo at high redshift. We find that photodetachment of H- by trapped Lyman alpha photons may lower the level of the H2-dissociating background radiation field required for DCBH formation substantially, dropping the critical flux by up to a factor of a few. This translates into a potentially large increase in the expected number density of DCBHs in the early Universe, and supports the view that DCBHs may be the seeds for the BHs residing in the centers of a significant fraction of galaxies today. We find that detachment of H- by Lyman alpha has the strongest impact on the critical flux for the relatively high background radiation temperatures expected to characterize the emission from young, hot stars in the early Universe. This lends support to the DCBH origin of the highest redshift quasars.

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Constraints on Primordial Black Holes with Extended Mass Functions

Published Paper #: 498

Authors:, Florian Kuhnel, Katherine Freese,

Journal: Phys. Rev. D 95, 083508 (2017)

url: http://arxiv.org/pdf/1701.07223v2.pdf

Abstract: Constraints on primordial black holes in the range $10^{-18} M_{\odot}$ to $10^{3} M_{\odot}$ are reevaluated for a general class of extended mass functions. Whereas previous work has assumed that PBHs are produced with one single mass, instead there is expected to be a range of masses even in the case of production from a single mechanism; constraints therefore change from previous literature. Although tightly constrained in the majority of cases, it is shown that, even under conservative assumptions, primordial black holes in the mass range $10^{-10} M_{\odot}$ to $10^{-8} M_{\odot}$ could still constitute the entirety of the dark matter. This stresses both the importance for a comprehensive reevaluation of all respective constraints that have previously been evaluated only for a monochromatic mass function, and the need to obtain more constraints in the allowed mass range.

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Reionization effect enhancement due to primordial black holes

Published Paper #: 497

Authors:, K. M. Belotsky, A. A. Kirillov, N. O. Nazarova, S. G. Rubin,

Journal: International Journal of Modern Physics D 26 (2017) 1750102

url: http://arxiv.org/pdf/1702.06338v1.pdf

Abstract: Primordial black holes (PBH) could account for variety of phenomena like dark matter, reionization of the Universe, early quasars, coalescence of black holes registered through gravitational waves recently. Each phenomenon relates to PBH of a specific mass range. PBH mass spectra varies in a wide range depending on specific model. Earlier we have shown that PBH with monochromatic mass distribution around $5\times 10^{16}$ g value allow to re-ionize the Universe moderately. Here we show that reionization effect and contribution to dark matter can be simultaneously enhanced with more natural extended mass distribution in the range around the same mass value.

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Stochastic gravitational waves associated with the formation of   primordial black holes

Published Paper #: 496

Authors:, Tomohiro Nakama, Joseph Silk, Marc Kamionkowski,

Journal: Phys. Rev. D 95, 043511 (2017)

url: http://arxiv.org/pdf/1612.06264v2.pdf

Abstract: Primordial black hole (PBH) mergers have been proposed as an explanation for the gravitational wave events detected by the LIGO collaboration. Such PBHs may be formed in the early Universe as a result of the collapse of extremely rare high-sigma peaks of primordial fluctuations on small scales, as long as the amplitude of primordial perturbations on small scales is enhanced significantly relative to the amplitude of perturbations observed on large scales. One consequence of these small-scale perturbations is generation of stochastic gravitational waves that arise at second order in scalar perturbations, mostly before the formation of the PBHs. These induced gravitational waves have been shown, assuming gaussian initial conditions, to be comparable to the current limits from the European Pulsar Timing Array, severely restricting this scenario. We show, however, that models with enhanced fluctuation amplitudes typically involve non-gaussian initial conditions. With such initial conditions, the current limits from pulsar timing can be evaded. The amplitude of the induced gravitational-wave background can be larger or smaller than the stochastic gravitational-wave background from supermassive black hole binaries.

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Antideuterons in cosmic rays: sources and discovery potential

Published Paper #: 495

Authors:, Johannes Herms, Alejandro Ibarra, Andrea Vittino, Sebastian Wild,

Journal: JCAP02(2017)018

url: http://arxiv.org/pdf/1610.00699v2.pdf

Abstract: Antibaryons are produced in our Galaxy in collisions of high energy cosmic rays with the interstellar medium and in old supernova remnants, and possibly, in exotic sources such as primordial black hole evaporation or dark matter annihilations and decays. The search for signals from exotic sources in antiproton data is hampered by large backgrounds from spallation which, within theoretical errors, can solely account for the current data. Due to the higher energy threshold for antideuteron production, which translates into a suppression of the low energy flux from spallations, antideuteron searches have been proposed as a probe for exotic sources. We perform in this paper a comprehensive analysis of the antideuteron fluxes at the Earth expected from known and hypothetical sources in our Galaxy, and we calculate their maximal values consistent with current antiproton data from AMS-02. We find that supernova remnants generate a negligible flux, whereas primordial black hole evaporation and dark matter annihilations or decays may dominate the total flux at low energies. On the other hand, we find that the detection of cosmic antideuterons would require, for the scenarios studied in this paper and assuming optimistic values of the coalescence momentum and solar modulation, an increase of the experimental sensitivity compared to ongoing and planned instruments by at least a factor of 2. Finally, we briefly comment on the prospects for antihelium-3 detection.

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Effect of lensing magnification on the apparent distribution of black   hole mergers

Published Paper #: 494

Authors:, Liang Dai, Tejaswi Venumadhav, Kris Sigurdson,

Journal: Phys. Rev. D 95, 044011 (2017)

url: http://arxiv.org/pdf/1605.09398v3.pdf

Abstract: The recent detection of gravitational waves indicates that stellar-mass black hole binaries are likely to be a key population of sources for forthcoming observations. With future upgrades, ground-based detectors could detect merging black hole binaries out to cosmological distances. Gravitational wave bursts from high redshifts ($z \gtrsim 1$) can be strongly magnified by gravitational lensing due to intervening galaxies along the line of sight. In the absence of electromagnetic counterparts, the mergers' intrinsic mass scale and redshift are degenerate with the unknown magnification factor $\mu$. Hence, strongly magnified low-mass mergers from high redshifts appear as higher-mass mergers from lower redshifts. We assess the impact of this degeneracy on the mass-redshift distribution of observable events for generic models of binary black hole formation from normal stellar evolution, Pop III star remnants, or a primordial black hole population. We find that strong magnification ($\mu \gtrsim 3$) generally creates a heavy tail of apparently massive mergers in the event distribution from a given detector. For LIGO and its future upgrades, this tail may dominate the population of intrinsically massive, but unlensed mergers in binary black hole formation models involving normal stellar evolution or primordial black holes. Modeling the statistics of lensing magnification can help account for this magnification bias when testing astrophysical scenarios of black hole binary formation and evolution.

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Cosmic microwave background limits on accreting primordial black holes

Published Paper #: 493

Authors:, Yacine Ali-Haïmoud, Marc Kamionkowski,

Journal: Phys. Rev. D 95, 043534 (2017)

url: http://arxiv.org/pdf/1612.05644v2.pdf

Abstract: Interest in the idea that primordial black holes (PBHs) might comprise some or all of the dark matter has recently been rekindled following LIGO's first direct detection of a binary-black-hole merger. Here we revisit the effect of accreting PBHs on the cosmic microwave background (CMB) frequency spectrum and angular temperature/polarization power spectra. We compute the accretion rate and luminosity of PBHs, accounting for their suppression by Compton drag and Compton cooling by CMB photons. We estimate the gas temperature near the Schwarzschild radius, and hence the free-free luminosity, accounting for the cooling resulting from collisional ionization when the background gas is mostly neutral. We account approximately for the velocities of PBHs with respect to the background gas. We provide a simple analytic estimate of the efficiency of energy deposition in the plasma. We find that the spectral distortions generated by accreting PBHs are too small to be detected by FIRAS, as well as by future experiments now being considered. We analyze Planck CMB temperature and polarization data and find, under our most conservative hypotheses, and at the order-of-magnitude level, that they rule out PBHs with masses >~ 10^2 M_sun as the dominant component of dark matter.

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Primordial GWs from universality classes of pseudo-scalar inflation

Published Paper #: 492

Authors:, Mauro Pieroni,

Journal: J.Phys.Conf.Ser. 840 (2017) no.1, 012033

url: http://arxiv.org/pdf/1701.09041v1.pdf

Abstract: In this contribution we discuss the possibility of generating an observable gravitational wave (GW) background by coupling a pseudo-scalar inflaton to some Abelian gauge fields. This analysis is performed by dividing inflationary models into universality classes. We find that of the most promising scenario is a Starobinsky-like model, which may lead to the generation of observational signatures both in upcoming CMB detectors as well as for direct GW detectors. The signal which can be produced in these models would both be observable in ground-based detectors, such as advanced LIGO, and in space-based detectors, such as LISA. The complementarity between the CMB and direct GW detection may be used to extract informations on the microphysics of inflation. Interestingly the mechanism discussed in this contribution may also be relevant for the generation of Primordial Black Holes (PBHs).

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Pulsar timing can constrain primordial black holes in the LIGO mass   window

Published Paper #: 491

Authors:, Katelin Schutz, Adrian Liu,

Journal: Phys. Rev. D 95, 023002 (2017)

url: http://arxiv.org/pdf/1610.04234v2.pdf

Abstract: The recent discovery of gravitational waves from merging black holes has generated interest in primordial black holes as a possible component of the dark matter. In this paper, we show that pulsar timing may soon have sufficient data to constrain $1$-$1000\,M_{\odot}$ primordial black holes via the non-detection of a third-order Shapiro time delay as the black holes move around the Galactic halo. We present the results of a Monte Carlo simulation which suggests that future data from known pulsars may be capable of constraining the PBH density more stringently than other existing methods in the mass range ~1-30$\,M_{\odot}$. We find that timing new pulsars discovered using the proposed Square Kilometre Array may constrain primordial black holes in this mass range to comprise less than ~1-10% of the dark matter.

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Dark Matter Density Spikes around Primordial Black Holes

Published Paper #: 490

Authors:, Yu. N. Eroshenko,

Journal: Astronomy Letters 42, 347 (2016)

url: http://arxiv.org/pdf/1607.00612v2.pdf

Abstract: We show that density spikes begin to form from dark matter particles around primordial black holes immediately after their formation at the radiation-dominated cosmological stage. This follows from the fact that in the thermal velocity distribution of particles there are particles with low velocities that remain in finite orbits around black holes and are not involved in the cosmological expansion. The accumulation of such particles near black holes gives rise to density spikes. These spikes are considerably denser than those that are formed later by the mechanism of secondary accretion. The density spikes must be bright gamma-ray sources. Comparison of the calculated signal from particle annihilation with the Fermi-LAT data constrains the present-day cosmological density parameter for primordial black holes with masses $M_{\rm BH}\geq10^{-8}M_\odot$ from above by values from $\Omega_{\rm BH}\leq1$ to $\Omega_{\rm BH}\leq10^{-8}$, depending on $M_{\rm BH}$. These constraints are several orders of magnitude more stringent than other known constraints.

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Science with the space-based interferometer LISA. IV: Probing inflation   with gravitational waves

Published Paper #: 489

Authors:, Nicola Bartolo, Chiara Caprini, Valerie Domcke, Daniel G. Figueroa, Juan Garcia-Bellido, Maria Chiara Guzzetti, Michele Liguori, Sabino Matarrese, Marco Peloso, Antoine Petiteau, Angelo Ricciardone, Mairi Sakellariadou, Lorenzo Sorbo, Gianmassimo Tasinato,

Journal: JCAP 12 (2016) 026

url: http://arxiv.org/pdf/1610.06481v2.pdf

Abstract: We investigate the potential for the LISA space-based interferometer to detect the stochastic gravitational wave background produced from different mechanisms during inflation. Focusing on well-motivated scenarios, we study the resulting contributions from particle production during inflation, inflationary spectator fields with varying speed of sound, effective field theories of inflation with specific patterns of symmetry breaking and models leading to the formation of primordial black holes. The projected sensitivities of LISA are used in a model-independent way for various detector designs and configurations. We demonstrate that LISA is able to probe these well-motivated inflationary scenarios beyond the irreducible vacuum tensor modes expected from any inflationary background.

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Planck Constraint on Relic Primordial Black Holes

Published Paper #: 488

Authors:, Steven Clark, Bhaskar Dutta, Yu Gao, Louis E. Strigari, Scott Watson,

Journal: Phys. Rev. D 95, 083006 (2017)

url: http://arxiv.org/pdf/1612.07738v1.pdf

Abstract: We investigate constraints on the abundance of primordial black holes (PBHs) in the mass range 10^{15}-10^{17} g using data from the Cosmic Microwave Background (CMB) and MeV extragalactic gamma-ray background (EGB). Hawking radiation from PBHs with lifetime greater than the age of the universe leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses \sim 10^{15}-10^{16} g, while the EGB dominates for masses \gtrsim 10^{16} g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses \sim 10^{16}-10^{17} g. Planned MeV gamma-ray observatories are ideal for further improving constraints on PBHs in this mass range.

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Solving puzzles of GW150914 by primordial black holes

Published Paper #: 487

Authors:, S. Blinnikov, A. Dolgov, N. K. Porayko, K. Postnov,

Journal: JCAP11(2016)036

url: http://arxiv.org/pdf/1611.00541v2.pdf

Abstract: The black hole binary properties inferred from the LIGO gravitational wave signal GW150914 posed several serious problems. The high masses and low effective spin of black hole binary can be explained if they are primordial (PBH) rather than the products of the stellar binary evolution. Such PBH properties are postulated ad hoc but not derived from fundamental theory. We show that the necessary features of PBHs naturally follow from the slightly modified Affleck-Dine (AD) mechanism of baryogenesis. The log-normal distribution of PBHs, predicted within the AD paradigm, is adjusted to provide an abundant population of low-spin stellar mass black holes. The same distribution gives a sufficient number of quickly growing seeds of supermassive black holes observed at high redshifts and may comprise an appreciable fraction of Dark Matter which does not contradict any existing observational limits. Testable predictions of this scenario are discussed.

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Supermassive black holes formed by direct collapse of inflationary   perturbations

Published Paper #: 486

Authors:, Tomohiro Nakama, Teruaki Suyama, Jun'ichi Yokoyama,

Journal: Phys. Rev. D 94, 103522 (2016)

url: http://arxiv.org/pdf/1609.02245v2.pdf

Abstract: We propose a mechanism of producing a new type of primordial perturbations that collapse to primordial black holes whose mass can be as large as necessary for them to grow to the supermassive black holes observed at high redshifts, without contradicting COBE/FIRAS upper limits on cosmic microwave background (CMB) spectral distortions. In our model, the observable Universe consists of two kinds of many small patches which experienced different expansion histories during inflation. Primordial perturbations large enough to form primordial black holes are realized on patches that experienced more Hubble expansion than the others. By making these patches the minor component, the rarity of supermassive black holes can be explained. On the other hand, most regions of the Universe experienced the standard history and, hence, only have standard almost-scale-invariant adiabatic perturbations confirmed by observations of CMB or large-scale structures of the Universe. Thus, our mechanism can evade the constraint from the nondetection of the CMB distortion set by the COBE/FIRAS measurement. Our model predicts the existence of supermassive black holes even at redshifts much higher than those observed. Hence, our model can be tested by future observations peeking into the higher-redshift Universe.

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Simple Cosmological Solution to the Higgs Instability Problem in the   Chaotic Inflation and Formation of Primordial Black Holes

Published Paper #: 485

Authors:, Masahiro Kawasaki, Kyohei Mukaida, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 94, 063509 (2016)

url: http://arxiv.org/pdf/1605.04974v3.pdf

Abstract: We revisit the compatibility between the chaotic inflation, which provides a natural solution to the initial condition problem, and the metastable electroweak vacuum, which is suggested by the results of LHC and the current mass measurements of top quark and Higgs boson. It is known that the chaotic inflation poses a threat to the stability of the electroweak vacuum because it easily generates large Higgs fluctuations during inflation or preheating and triggers the catastrophic vacuum decay. In this paper, we propose a simple cosmological solution in which the vacuum is stabilized during chaotic inflation, preheating and after that. This simple solution naturally predicts the formation of primordial black holes. We find interesting parameter regions where the present dark matter density is provided by them. Also, the thermal leptogenesis can be accommodated in our scenario.

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The Black Hole Mass Function from Gravitational Wave Measurements

Published Paper #: 484

Authors:, Ely D. Kovetz, Ilias Cholis, Patrick C. Breysse, Marc Kamionkowski,

Journal: Phys. Rev. D 95, 103010 (2017)

url: http://arxiv.org/pdf/1611.01157v1.pdf

Abstract: We examine how future gravitational-wave measurements from merging black holes (BHs) can be used to infer the shape of the black-hole mass function, with important implications for the study of star formation and evolution and the properties of binary BHs. We model the mass function as a power law, inherited from the stellar initial mass function, and introduce lower and upper mass cutoff parameterizations in order to probe the minimum and maximum BH masses allowed by stellar evolution, respectively. We initially focus on the heavier BH in each binary, to minimize model dependence. Taking into account the experimental noise, the mass measurement errors and the uncertainty in the redshift-dependence of the merger rate, we show that the mass function parameters, as well as the total rate of merger events, can be measured to <10% accuracy within a few years of advanced LIGO observations at its design sensitivity. This can be used to address important open questions such as the upper limit on the stellar mass which allows for BH formation and to confirm or refute the currently observed mass gap between neutron stars and BHs. In order to glean information on the progenitors of the merging BH binaries, we then advocate the study of the two-dimensional mass distribution to constrain parameters that describe the two-body system, such as the mass ratio between the two BHs, in addition to the merger rate and mass function parameters. We argue that several years of data collection can efficiently probe models of binary formation, and show, as an example, that the hypothesis that some gravitational-wave events may involve primordial black holes can be tested. Finally, we point out that in order to maximize the constraining power of the data, it may be worthwhile to lower the signal-to-noise threshold imposed on each candidate event and amass a larger statistical ensemble of BH mergers.

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PBH Dark Matter in Supergravity Inflation Models

Published Paper #: 483

Authors:, Masahiro Kawasaki, Alexander Kusenko, Yuichiro Tada, Tsutomu T. Yanagida,

Journal: Phys. Rev. D 94, 083523 (2016)

url: http://arxiv.org/pdf/1606.07631v2.pdf

Abstract: We propose a novel scenario to produce abundant primordial black holes (PBHs) in new inflation which is a second phase of a double inflation in the supergravity frame work. In our model, some preinflation phase before the new inflation is assumed and it would be responsible for the primordial curvature perturbations on the cosmic microwave background scale, while the new inflation produces only the small scale perturbations. Our new inflation model has linear, quadratic, and cubic terms in its potential and PBH production corresponds with its flat inflection point. The linear term can be interpreted to come from a supersymmetry-breaking sector, and with this assumption, the vanishing cosmological constant condition after inflation and the flatness condition for the inflection point can be consistently satisfied.

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The clustering of massive Primordial Black Holes as Dark Matter:   measuring their mass distribution with Advanced LIGO

Published Paper #: 482

Authors:, Sebastien Clesse, Juan García-Bellido,

Journal: Physics of the Dark Universe 10 (2016) 002

url: http://arxiv.org/pdf/1603.05234v2.pdf

Abstract: The recent detection by Advanced LIGO of gravitational waves (GW) from the merging of a binary black hole system sets new limits on the merging rates of massive primordial black holes (PBH) that could be a significant fraction or even the totality of the dark matter in the Universe. aLIGO opens the way to the determination of the distribution and clustering of such massive PBH. If PBH clusters have a similar density to the one observed in ultra-faint dwarf galaxies, we find merging rates comparable to aLIGO expectations. Massive PBH dark matter predicts the existence of thousands of those dwarf galaxies where star formation is unlikely because of gas accretion onto PBH, which would possibly provide a solution to the missing satellite and too-big-to-fail problems. Finally, we study the possibility of using aLIGO and future GW antennas to measure the abundance and mass distribution of PBH in the range [5 - 200] Msun to 10\% accuracy.

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Gravitational wave production by Hawking radiation from rotating   primordial black holes

Published Paper #: 481

Authors:, Ruifeng Dong, William H. Kinney, Dejan Stojkovic,

Journal: JCAP10(2016)034

url: http://arxiv.org/pdf/1511.05642v3.pdf

Abstract: In this paper we analyze in detail a rarely discussed question of gravity wave production from evaporating primordial black holes. These black holes emit gravitons which are, at classical level, registered as gravity waves. We use the latest constraints on their abundance, and calculate the power emitted in gravitons at the time of their evaporation. We then solve the coupled system of equations that gives us the evolution of the frequency and amplitude of gravity waves during the expansion of the universe. The spectrum of gravitational waves that can be detected today depends on multiple factors: fraction of the total energy density which was occupied by primordial black holes, the epoch in which they were formed, and quantities like their mass and angular momentum. We conclude that very small primordial black holes which evaporate before the big-bang nucleosynthesis emit gravitons whose spectral energy fraction today can be as large as $10^{-7.5}$. On the other hand, those which are massive enough so that they still exist now can yield a signal as high as $10^{-6.5}$. However, typical frequencies of the gravity waves from primordial black holes are still too high to be observed with the current and near future gravity wave observations.

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Microlensing and dynamical constraints on primordial black hole dark   matter with an extended mass function

Published Paper #: 480

Authors:, Anne M. Green,

Journal: Phys. Rev. D 94, 063530 (2016)

url: http://arxiv.org/pdf/1609.01143v2.pdf

Abstract: The recent discovery of gravitational waves from mergers of $\sim 10 \, M_{\odot}$ black hole binaries has stimulated interested in Primordial Black Hole dark matter in this mass range. Microlensing and dynamical constraints exclude all of the dark matter being in compact objects with a delta function mass function in the range $10^{-7} \lesssim M/ M_{\odot} \lesssim 10^{5}$. However it has been argued that all of the dark matter could be composed of compact objects in this range with an extended mass function. We explicitly recalculate the microlensing and dynamical constraints for compact objects with an extended mass function which replicates the PBH mass function produced by inflation models. We find that the microlensing and dynamical constraints place conflicting constraints on the width of the mass function, and do not find a mass function which satisfies both constraints.

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Do Some AGN Lack X-ray Emission?

Published Paper #: 479

Authors:, Charlotte Simmonds, Franz E. Bauer, Trinh X. Thuan, Yuri I. Izotov, Daniel Stern, Fiona A. Harrison,

Journal: A&A 596, A64 (2016)

url: http://arxiv.org/pdf/1609.07619v1.pdf

Abstract: $Context:$ Intermediate-Mass Black Holes (IMBHs) are thought to be the seeds of early Supermassive Black Holes (SMBHs). While $\gtrsim$100 IMBH and small SMBH candidates have been identified in recent years, few have been robustly confirmed to date, leaving their number density in considerable doubt. Placing firmer constraints both on the methods used to identify and confirm IMBHs/SMBHs, as well as characterizing the range of host environments that IMBHs/SMBHs likely inhabit is therefore of considerable interest and importance. Additionally, finding significant numbers of IMBHs in metal-poor systems would be particularly intriguing, since such systems may represent local analogs of primordial galaxies, and therefore could provide clues of early accretion processes.   $Aims:$ Here we study in detail several candidate Active Galactic Nuclei (AGN) found in metal-poor hosts.   $Methods:$ We utilize new X-ray and optical observations to characterize these metal-poor AGN candidates and compare them against known AGN luminosity relations and well-characterized IMBH/SMBH samples.   $Results:$ Despite having clear broad optical emission lines that are long-lived ($\gtrsim$10--13\,yr), these candidate AGN appear to lack associated strong X-ray and hard UV emission, lying at least 1--2 dex off the known AGN correlations. If they are IMBHs/SMBHs, our constraints imply that they either are not actively accreting, their accretion disks are fully obscured along our line-of-sight, or their accretion disks are not producing characteristic high energy emission. Alternatively, if they are not AGN, then their luminous broad emission lines imply production by extreme stellar processes. The latter would have profound implications on the applicability of broad lines for mass estimates of massive black holes.

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Spherical and nonspherical models of primordial black hole formation:   exact solutions

Published Paper #: 478

Authors:, Tomohiro Harada, Sanjay Jhingan,

Journal: Prog.Theor.Exp.Phys. (2016) 093E04

url: http://arxiv.org/pdf/1512.08639v2.pdf

Abstract: We construct spacetimes which provide spherical and nonspherical models of black hole formation in the flat Friedmann--Lemaitre--Robertson--Walker (FLRW) universe with the Lemaitre--Tolman--Bondi solution and the Szekeres quasispherical solution, respectively. These dust solutions may contain both shell-crossing and shell-focusing naked singularities. These singularities can be physically regarded as the breakdown of dust description, where strong pressure gradient force plays a role. We adopt the simultaneous big bang condition to extract a growing mode of adiabatic perturbation in the flat FLRW universe. If the density perturbation has a sufficiently homogeneous central region and a sufficiently sharp transition to the background FLRW universe, its central shell-focusing singularity is globally covered. If the density concentration is sufficiently large, no shell-crossing singularity appears and a black hole is formed. If the density concentration is not sufficiently large, a shell-crossing singularity appears. In this case, a large dipole moment significantly advances shell-crossing singularities and they tend to appear before the black hole formation. In contrast, a shell-crossing singularity unavoidably appears in the spherical and nonspherical evolution of cosmological voids. The present analysis is general and applicable to cosmological nonlinear structure formation described by these dust solutions.

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Shocks in the Early Universe

Published Paper #: 477

Authors:, Ue-Li Pen, Neil Turok,

Journal: Phys. Rev. Lett. 117, 131301 (2016)

url: http://arxiv.org/pdf/1510.02985v2.pdf

Abstract: We point out a surprising consequence of the usually assumed initial conditions for cosmological perturbations. Namely, a spectrum of Gaussian, linear, adiabatic, scalar, growing mode perturbations not only creates acoustic oscillations of the kind observed on very large scales today, it also leads to the production of shocks in the radiation fluid of the very early universe. Shocks cause departures from local thermal equilibrium as well as creating vorticity and gravitational waves. For a scale-invariant spectrum and standard model physics, shocks form for temperatures $1$ GeV$<T<10^{7}$ GeV. For more general power spectra, such as have been invoked to form primordial black holes, shock formation and the consequent gravitational wave emission provides a signal detectable by current and planned gravitational wave experiments, allowing them to strongly constrain conditions present in the primordial universe as early as $10^{-30}$ seconds after the big bang.

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Stochastic Gravitational-Wave Background due to Primordial Binary Black   Hole Mergers

Published Paper #: 476

Authors:, Vuk Mandic, Simeon Bird, Ilias Cholis,

Journal: Phys. Rev. Lett. 117, 201102 (2016)

url: http://arxiv.org/pdf/1608.06699v1.pdf

Abstract: Recent Advanced LIGO detections of binary black hole mergers have prompted multiple studies investigating the possibility that the heavy GW150914 binary system was of primordial origin, and hence could be evidence for dark matter in the form of black holes. We compute the stochastic background arising from the incoherent superposition of such primordial binary black hole systems in the universe and compare it to the similar background spectrum due to binary black hole systems of stellar origin. We investigate the possibility of detecting this background with future gravitational wave detectors, and discuss the possibility of using the stochastic gravitational-wave background measurement to constrain the dark matter component in the form of black holes.

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Constraining the Rate of Primordial Black-Hole Explosions and Extra   Dimension Scale using a Low-Frequency Radio Antenna Array

Published Paper #: 475

Authors:, Sean E. Cutchin, John H. Simonetti, Steven W. Ellingson, Amanda S. Larracuente, Michael J. Kavic,

Journal: PASP 127 1269 (2015)

url: http://arxiv.org/pdf/1608.01945v3.pdf

Abstract: An exploding primordial black-hole (PBH) may produce a single pulse of electromagnetic radiation detectable at the low-frequency end of the radio spectrum. Furthermore, a radio transient from an exploding PBH could be a signature of an extra spatial dimension. We describe here an approach for searching for PBH explosions using a low-frequency radio antenna array, and as a practical example, the results of a such a search using the Eight-meter-wavelength Transient Array (ETA). No compelling astrophysical signal was detected in $\approx 4$ hours of data implying an observational upper limit on the rate of exploding PBHs is $4.2 \times 10^{-7} \,\rm{pc}^{-3}\,\rm{yr}^{-1}$ for an exploding PBH with a fireball Lorentz factor of $10^{4.5}$ for the standard scenario of Page and Hawking. This rate limit is the strongest constraint yet set for PBH explosions with this fireball Lorentz factor. Observations ($\sim300$ hours) using the Arecibo Observatory were used to set a stronger constraint on the rate of PBH explosions for a fireball Lorentz factor of $10^{4.6}$ but the limit set by those observations for the fireball Lorentz factor considered here are less stringent by more than an order of magnitude. The limits considered here are applicable to exploding PBHs in the halo of the Galaxy. These observations also imply an upper limit of $2.0 \times 10^{-4} \,\rm{pc}^{-3}\,\rm{yr}^{-1}$ on the rate of PBH explosions in the context of certain extra dimension models as described by Kavic et al. This rate limit is for a fireball Lorentz factor of $10^{4.3}$ which corresponds to an extra dimension compactification scale of $3.0 \times 10^{-18}$m.

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Primordial black holes as a novel probe of primordial gravitational   waves. II: Detailed analysis

Published Paper #: 474

Authors:, Tomohiro Nakama, Teruaki Suyama,

Journal: Phys. Rev. D 94, 043507 (2016)

url: http://arxiv.org/pdf/1605.04482v2.pdf

Abstract: Recently we have proposed a novel method to probe primordial gravitational waves from upper bounds on the abundance of primordial black holes (PBHs). When the amplitude of primordial tensor perturbations generated in the early Universe is fairly large, they induce substantial scalar perturbations due to their second-order effects. If these induced scalar perturbations are too large when they reenter the horizon, then PBHs are overproduced, their abundance exceeding observational upper limits. That is, primordial tensor perturbations on superhorizon scales can be constrained from the absence of PBHs. In our recent paper we have only shown simple estimations of these new constraints, and hence in this paper, we present detailed derivations, solving the Einstein equations for scalar perturbations induced at second order in tensor perturbations. We also derive an approximate formula for the probability density function of induced density perturbations, necessary to relate the abundance of PBHs to the primordial tensor power spectrum, assuming primordial tensor perturbations follow Gaussian distributions. Our new upper bounds from PBHs are compared with other existing bounds obtained from big bang nucleosynthesis, cosmic microwave background, LIGO/Virgo and pulsar timing arrays.

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Trapping effects in inflation: blue spectrum at small scales

Published Paper #: 473

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys. Rev. D 94, 023517 (2016)

url: http://arxiv.org/pdf/1511.06175v2.pdf

Abstract: We consider the inflationary model in which the inflaton $\phi$ couples to another scalar field $\chi$ via the interaction $g^2(\phi-\phi_0)^2\chi^2$ with a small coupling constant $g$ ($g^2 \sim 10^{-7}$). We assume that there is a sequence of "trapping points" $\phi_{0i}$ along the inflationary trajectory where particles of $\chi$-field become massless and are rather effectively produced. We calculate the power spectrum of inflaton field fluctuations originated from a backreaction of $\chi$-particles produced, using the Schwinger's "in-in" formalism. We show that the primary curvature power spectrum produced by these backreaction effects is blue, which leads to a strong overproduction of primordial black holes (PBHs) in subsequent radiation era.

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Orbital eccentricities in primordial black holes binaries

Published Paper #: 472

Authors:, Ilias Cholis, Ely D. Kovetz, Yacine Ali-Haïmoud, Simeon Bird, Marc Kamionkowski, Julian B. Muñoz, Alvise Raccanelli,

Journal: Phys. Rev. D 94, 084013 (2016)

url: http://arxiv.org/pdf/1606.07437v1.pdf

Abstract: It was recently suggested that the merger of $\sim30\,M_\odot$ primordial black holes (PBHs) may provide a significant number of events in gravitational-wave observatories over the next decade, if they make up an appreciable fraction of the dark matter. Here we show that measurement of the eccentricities of the inspiralling binary black holes can be used to distinguish these binaries from those produced by more traditional astrophysical mechanisms. These PBH binaries are formed on highly eccentric orbits and can then merge on timescales that in some cases are years or less, retaining some eccentricity in the last seconds before the merger. This is to be contrasted with massive-stellar-binary, globular-cluster, or other astrophysical origins for binary black holes (BBHs) in which the orbits have very effectively circularized by the time the BBH enters the observable LIGO window. Here we discuss the features of the gravitational-wave signals that indicate this eccentricity and forecast the sensitivity of LIGO and the Einstein Telescope to such effects. We show that if PBHs make up the dark matter, then roughly one event should have a detectable eccentricity given LIGO's expected sensitivity and observing time of six years. The Einstein Telescope should see $O(10)$ such events after ten years.

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Did LIGO detect dark matter?

Published Paper #: 471

Authors:, Simeon Bird, Ilias Cholis, Julian B. Muñoz, Yacine Ali-Haïmoud, Marc Kamionkowski, Ely D. Kovetz, Alvise Raccanelli, Adam G. Riess,

Journal: Phys. Rev. Lett. 116, 201301 (2016)

url: http://arxiv.org/pdf/1603.00464v2.pdf

Abstract: We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains a window for masses $20\,M_\odot \lesssim M_{\rm bh} \lesssim 100\, M_\odot$ where primordial black holes (PBHs) may constitute the dark matter. If two BHs in a galactic halo pass sufficiently close, they radiate enough energy in gravitational waves to become gravitationally bound. The bound BHs will rapidly spiral inward due to emission of gravitational radiation and ultimately merge. Uncertainties in the rate for such events arise from our imprecise knowledge of the phase-space structure of galactic halos on the smallest scales. Still, reasonable estimates span a range that overlaps the $2-53$ Gpc$^{-3}$ yr$^{-1}$ rate estimated from GW150914, thus raising the possibility that LIGO has detected PBH dark matter. PBH mergers are likely to be distributed spatially more like dark matter than luminous matter and have no optical nor neutrino counterparts. They may be distinguished from mergers of BHs from more traditional astrophysical sources through the observed mass spectrum, their high ellipticities, or their stochastic gravitational wave background. Next generation experiments will be invaluable in performing these tests.

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Primordial black holes as a novel probe of primordial gravitational   waves

Published Paper #: 470

Authors:, Tomohiro Nakama, Teruaki Suyama,

Journal: Phys. Rev. D 92, 121304 (2015)

url: http://arxiv.org/pdf/1506.05228v2.pdf

Abstract: We propose a novel method to probe primordial gravitational waves by means of primordial black holes (PBHs). When the amplitude of primordial tensor perturbations on comoving scales much smaller than those relevant to Cosmic Microwave Background is very large, it induces scalar perturbations due to second-order effects substantially. If the amplitude of resultant scalar perturbations becomes too large, then PBHs are overproduced to a level that is inconsistent with a variety of existing observations constraining their abundance. This leads to upper bounds on the amplitude of initial tensor perturbations on super-horizon scales. These upper bounds from PBHs are compared with other existing bounds.

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LIGO gravitational wave detection, primordial black holes and the   near-IR cosmic infrared background anisotropies

Published Paper #: 469

Authors:, A. Kashlinsky,

Journal: ApJLetters, 823, L25 (2016)

url: http://arxiv.org/pdf/1605.04023v1.pdf

Abstract: LIGO's discovery of a gravitational wave from two merging black holes (BHs) of similar masses rekindled suggestions that primordial BHs (PBHs) make up the dark matter (DM). If so, PBHs would add a Poissonian isocurvature density fluctuation component to the inflation-produced adiabatic density fluctuations. For LIGO's BH parameters, this extra component would dominate the small-scale power responsible for collapse of early DM halos at z>10, where first luminous sources formed. We quantify the resultant increase in high-z abundances of collapsed halos that are suitable for producing the first generation of stars and luminous sources. The significantly increased abundance of the early halos would naturally explain the observed source-subtracted near-IR cosmic infrared background (CIB) fluctuations, which cannot be accounted for by known galaxy populations. For LIGO's BH parameters this increase is such that the observed CIB fluctuation levels at 2 to 5 micron can be produced if only a tiny fraction of baryons in the collapsed DM halos forms luminous sources. Gas accretion onto these PBHs in collapsed halos, where first stars should also form, would straightforwardly account for the observed high coherence between the CIB and unresolved cosmic X-ray background in soft X-rays. We discuss modifications possibly required in the processes of first star formation if LIGO-type BHs indeed make up the bulk or all of DM. The arguments are valid only if the PBHs make up all, or at least most, of DM, but at the same time the mechanism appears inevitable if DM is made of PBHs.

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Effects of Critical Collapse on Primordial Black-Hole Mass Spectra

Published Paper #: 468

Authors:, Florian Kuhnel, Cornelius Rampf, Marit Sandstad,

Journal: Eur.Phys.J. C76 (2016) 2, 93

url: http://arxiv.org/pdf/1512.00488v4.pdf

Abstract: Certain inflationary models as well as realisations of phase transitions in the early Universe predict the formation of primordial black holes. For most mass ranges, the fraction of matter in the form of primordial black holes is limited by many different observations on various scales. Primordial black holes are assumed to be formed when overdensities that cross the horizon have Schwarzschild radii larger than the horizon. Traditionally it was therefore assumed that primordial black-hole masses were equal to the horizon mass at their time of formation. However, detailed calculations of their collapse show that primordial black holes formed at each point in time should rather form a spectrum of different masses, obeying critical scaling. Though this has been known for more than fifteen years, the effect of this scaling behaviour is largely ignored when considering predictions for primordial black hole mass spectra. In this paper we consider the critical collapse scaling for a variety of models which produce primordial black holes, and find that it generally leads to a shift, broadening and an overall decrease of the mass contained in primordial black holes. This effect is model and parameter dependent and cannot be contained by a constant rescaling of the spectrum; it can become important and should be taken into account when comparing to observational constraints.

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On Ellipsoidal Collapse and Primordial Black-Hole Formation

Published Paper #: 467

Authors:, Florian Kuhnel, Marit Sandstad,

Journal: Phys. Rev. D 94, 063514 (2016)

url: http://arxiv.org/pdf/1602.04815v3.pdf

Abstract: We reinvestigate gravitational ellipsoidal collapse with special focus on its impact on primordial black-hole formation. For a generic model we demonstrate that the abundance and energy density of the produced primordial black holes will be significantly decreased when the non-sphericity of the overdensities is taken into account.

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Determining the progenitors of merging black-hole binaries

Published Paper #: 466

Authors:, Alvise Raccanelli, Ely D. Kovetz, Simeon Bird, Ilias Cholis, Julian B. Munoz,

Journal: Phys. Rev. D 94, 023516 (2016)

url: http://arxiv.org/pdf/1605.01405v1.pdf

Abstract: We investigate a possible method for determining the progenitors of black hole (BH) mergers observed via their gravitational wave (GW) signal. We argue that measurements of the cross-correlation of the GW events with overlapping galaxy catalogs may provide an additional tool in determining if BH mergers trace the stellar mass of the Universe, as would be expected from mergers of the endpoints of stellar evolution. If on the other hand the BHs are of primordial origin, as has been recently suggested, their merging would be preferentially hosted by lower biased objects, and thus have a lower cross-correlation with luminous galaxies. Here we forecast the expected precision of the cross-correlation measurement for current and future GW detectors such as LIGO and the Einstein Telescope. We then predict how well these instruments can distinguish the model that identifies high-mass BH-BH mergers as the merger of primordial black holes that constitute the dark matter in the Universe from more traditional astrophysical sources.

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Constraints on primordial black holes from Galactic gamma-ray background

Published Paper #: 465

Authors:, B. J. Carr, Kazunori Kohri, Yuuiti Sendouda, Jun'ichi Yokoyama,

Journal: Phys. Rev. D 94, 044029 (2016)

url: http://arxiv.org/pdf/1604.05349v1.pdf

Abstract: The fraction of the Universe going into primordial black holes (PBHs) with initial mass M_* \approx 5 \times 10^{14} g, such that they are evaporating at the present epoch, is strongly constrained by observations of both the extragalactic and Galactic gamma-ray backgrounds. However, while the dominant contribution to the extragalactic background comes from the time-integrated emission of PBHs with initial mass M_*, the Galactic background is dominated by the instantaneous emission of those with initial mass slightly larger than M_* and current mass below M_*. Also, the instantaneous emission of PBHs smaller than 0.4 M_* mostly comprises secondary particles produced by the decay of directly emitted quark and gluon jets. These points were missed in the earlier analysis by Lehoucq et al. using EGRET data. For a monochromatic PBH mass function, with initial mass (1+\mu) M_* and \mu << 1, the current mass is (3\mu)^{1/3} M_* and the Galactic background constrains the fraction of the Universe going into PBHs as a function of \mu. However, the initial mass function cannot be precisely monochromatic and even a tiny spread of mass around M_* would generate a current low-mass tail of PBHs below M_*. This tail would be the main contributor to the Galactic background, so we consider its form and the associated constraints for a variety of scenarios with both extended and nearly-monochromatic initial mass functions. In particular, we consider a scenario in which the PBHs form from critical collapse and have a mass function which peaks well above M_*. In this case, the largest PBHs could provide the dark matter without the M_* ones exceeding the gamma-ray background limits.

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Primordial Black Holes Formation from Particle Production during   Inflation

Published Paper #: 464

Authors:, Encieh Erfani,

Journal: JCAP04(2016)020

url: http://arxiv.org/pdf/1511.08470v2.pdf

Abstract: We study the possibility that particle production during inflation can source the required power spectrum for dark matter (DM) primordial black holes (PBH) formation. We consider the scalar and the gauge quanta production in inflation models, where in the latter case, we focus in two sectors: inflaton coupled i) directly and ii) gravitationally to a $U(1)$ gauge field. We do not assume any specific potential for the inflaton field. Hence, in the gauge production case, in a model independent way we show that the non-production of DM PBHs puts stronger upper bound on the particle production parameter. Our analysis show that this bound is more stringent than the bounds from the bispectrum and the tensor-to-scalar ratio derived by gauge production in these models. In the scenario where the inflaton field coupled to a scalar field, we put an upper bound on the amplitude of the generated scalar power spectrum by non-production of PBHs. As a by-product we also show that the required scalar power spectrum for PBHs formation is lower when the density perturbations are non-Gaussian in comparison to the Gaussian density perturbations.

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Non-thermal WIMPs and Primordial Black Holes

Published Paper #: 463

Authors:, Julian Georg, Gizem Şengör, Scott Watson,

Journal: Phys. Rev. D 93, 123523 (2016)

url: http://arxiv.org/pdf/1603.00023v1.pdf

Abstract: Non-thermal histories for the early universe have received notable attention as they are a rich source of phenomenology, while also being well motivated by top-down approaches to beyond the Standard Model physics. The early (pre-BBN) matter phase in these models leads to enhanced growth of density perturbations on sub-Hubble scales. Here we consider whether primordial black hole formation associated with the enhanced growth is in conflict with existing observations. Such constraints depend on the tilt of the primordial power spectrum, and we find that non-thermal histories are tightly constrained in the case of a significantly blue spectrum. Alternatively, if dark matter is taken to be of non-thermal origin we can restrict the primordial power spectrum on scales inaccessible to CMB and LSS observations. We establish constraints for a wide range of scalar masses (reheat temperatures) with the most stringent bounds resulting from the formation of $10^{15}$ g black holes. These black holes would be evaporating today and are constrained by FERMI observations. We also consider whether the breakdown of the coherence of the scalar oscillations on sub-horizon scales can lead to a Jean's pressure preventing black hole formation and relaxing our constraints. Our main conclusion is that primordial black hole constraints, combined with existing constraints on non-thermal WIMPs, favor a primordial spectrum closer to scale invariance or a red tilted spectrum.

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Phenomenology of bouncing black holes in quantum gravity: a closer look

Published Paper #: 462

Authors:, Aurelien Barrau, Boris Bolliet, Francesca Vidotto, Celine Weimer,

Journal: JCAP02(2016)022

url: http://arxiv.org/pdf/1507.05424v3.pdf

Abstract: It was recently shown that black holes could be bouncing stars as a consequence of quantum gravity. We investigate the astrophysical signals implied by this hypothesis, focusing on primordial black holes. We consider different possible bounce times and study the integrated diffuse emission.

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White Holes as the Asymptotic Limit of Evaporating Primordial Black   Holes

Published Paper #: 461

Authors:, Jeffrey S. Lee, Gerald B. Cleaver,

Journal: International Journal of Modern Physics A Vol. 31 (2016) 1650162

url: http://arxiv.org/pdf/1602.05505v1.pdf

Abstract: This paper examines the interaction of an intense fermion field with all of the particle species of an attometer primordial black hole's (PBH)'s high energy Hawking radiation spectrum. By extrapolating to Planck-sized PBH's, it is shown that, although Planck-sized PBH's closely simulate the zero absorption requirement of white holes, the absorption probability is not truly zero, and therefore, thermodynamically, Planck-sized PBH's are not true white holes.

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The DRAGON simulations: globular cluster evolution with a million stars

Published Paper #: 460

Authors:, Long Wang, Rainer Spurzem, Sverre Aarseth, Mirek Giersz, Abbas Askar, Peter Berczik, Thorsten Naab, Riko Schadow, M. B. N. Kouwenhoven,

Journal: MNRAS 458, 1450-1465 (2016)

url: http://arxiv.org/pdf/1602.00759v1.pdf

Abstract: Introducing the DRAGON simulation project, we present direct $N$-body simulations of four massive globular clusters (GCs) with $10^6$ stars and 5$\%$ primordial binaries at a high level of accuracy and realism. The GC evolution is computed with NBODY6++GPU and follows the dynamical and stellar evolution of individual stars and binaries, kicks of neutron stars and black holes, and the effect of a tidal field. We investigate the evolution of the luminous (stellar) and dark (faint stars and stellar remnants) GC components and create mock observations of the simulations (i.e. photometry, color-magnitude diagrams, surface brightness and velocity dispersion profiles). By connecting internal processes to observable features we highlight the formation of a long-lived 'dark' nuclear subsystem made of black holes (BHs), which results in a two-component structure. The inner core is dominated by the BH subsystem and experiences a core collapse phase within the first Gyr. It can be detected in the stellar (luminous) line-of-sight velocity dispersion profiles. The outer extended core - commonly observed in the (luminous) surface brightness profiles - shows no collapse features and is continuously expanding. We demonstrate how a King (1966) model fit to observed clusters might help identify the presence of post core-collapse BH subsystems. For global observables like core and half-mass radii the direct simulations agree well with Monte-Carlo models. Variations in the initial mass function can result in significantly different GC properties (e.g. density distributions) driven by varying amounts of early mass loss and the number of forming BHs.

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A numerical study of pseudoscalar inflation with an axion-gauge field   coupling

Published Paper #: 459

Authors:, Shu-Lin Cheng, Wolung Lee, Kin-Wang Ng,

Journal: Phys. Rev. D 93, 063510 (2016)

url: http://arxiv.org/pdf/1508.00251v2.pdf

Abstract: A numerical study of a pseudoscalar inflation having an axion-photon-like coupling is performed by solving numerically the coupled differential equations of motion for inflaton and photon mode functions from the onset of inflation to the end of reheating. The backreaction due to particle production is also included self-consistently. We find that this particular inflation model realizes the idea of a warm inflation in which a steady thermal bath is established by the particle production. In most cases this thermal bath exceeds the amount of radiation released in the reheating process. In the strong coupling regime, the transition from the inflationary to the radiation-dominated phase does not involve either a preheating or reheating process. In addition, energy density peaks produced near the end of inflation may lead to the formation of primordial black holes.

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Baryon number conservation in Bose-Einstein condensate black holes

Published Paper #: 458

Authors:, Florian Kühnel, Marit Sandstad,

Journal: Phys. Rev. D 92, 124028 (2015)

url: http://arxiv.org/pdf/1506.08823v2.pdf

Abstract: Primordial black holes are studied in the Bose-Einstein condensate description of space-time. The question of baryon-number conservation is investigated with emphasis on possible formation of bound states of the system's remaining captured baryons. This leads to distinct predictions for both the formation time, which for the naively natural assumptions is shown to lie between $10^{-12}\.\srm$ to $10^{12}\.\srm$ after Big Bang, as well as for the remnant's mass, yielding approximately $3 \cdot 10^{23}\.{\rm kg}$ in the same scheme. The consequences for astrophysically formed black holes are also considered.

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How can young massive clusters reach their present-day sizes?

Published Paper #: 457

Authors:, Sambaran Banerjee, Pavel Kroupa,

Journal: A&A 597, A28 (2017)

url: http://arxiv.org/pdf/1510.04293v1.pdf

Abstract: The classic question that how young massive star clusters attain their shapes and sizes, as we find them today, remains to be a challenge. Both observational and computational studies of star-forming massive molecular gas clouds infer that massive cluster formation is primarily triggered along the small-scale ($\lesssim0.3$ pc) filamentary substructures within the clouds. The present study is intended to investigate the possible ways in which a filament-like-compact, massive star cluster (effective radius 0.1-0.3 pc) can expand $\gtrsim10$ times, still remaining massive enough ($\gtrsim10^4 M_\odot$), to become a young massive star cluster, as we observe today. To that end, model massive clusters (of initially $10^4 M_\odot-10^5 M_\odot$) are evolved using Sverre Aarseth's state-of-the-art N-body code NBODY7. All the computed clusters expand with time, whose sizes (effective radii) are compared with those observed for young massive clusters, of age $\lesssim100$ Myr, in the Milky Way and other nearby galaxies. It is found that beginning from the above compact sizes, a star cluster cannot expand by its own, i.e., due to two-body relaxation, stellar-evolutionary mass loss, dynamical heating by primordial binaries and stellar-mass black holes, up to the observed sizes of young massive clusters; they always remain much more compact compared to the observed ones. This calls for additional mechanisms that can boost the expansion of a massive cluster after its assembly. Using further N-body calculations, it is shown that a substantial residual gas expulsion, with $\approx30$% star formation efficiency, can indeed swell the newborn embedded cluster adequately. The limitations of the present calculations and their consequences are discussed.

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The chemical evolution of self-gravitating primordial disks

Published Paper #: 456

Authors:, Dominik R. G. Schleicher, Stefano Bovino, Muhammad A. Latif, Andrea Ferrara, Tommaso Grassi,

Journal: A&A 585, A11 (2016)

url: http://arxiv.org/pdf/1504.06296v2.pdf

Abstract: Numerical simulations show the formation of self-gravitating primordial disks during the assembly of the first structures in the Universe, in particular during the formation of Pop.~III and supermassive stars. Their subsequent evolution is expected to be crucial to determine the mass scale of the first cosmological objects, which depends on the temperature of the gas and the dominant cooling mechanism. Here, we derive a one-zone framework to explore the chemical evolution of such disks and show that viscous heating leads to the collisional dissociation of an initially molecular gas. The effect is relevant on scales of 10 AU (1000 AU) for a central mass of 10 M_sun (10^4 M_sun) at an accretion rate of 10^{-1} M_sun yr^{-1}, and provides a substantial heat input to stabilize the disk. If the gas is initially atomic, it remains atomic during the further evolution, and the effect of viscous heating is less significant. The additional thermal support is particularly relevant for the formation of very massive objects, such as the progenitors of the first supermassive black holes. The stabilizing impact of viscous heating thus alleviates the need for a strong radiation background as a means of keeping the gas atomic.

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Regular black hole remnants and graviatoms with de Sitter interior as   heavy dark matter candidates probing inhomogeneity of early universe

Published Paper #: 455

Authors:, Irina Dymnikova, Maxim Khlopov,

Journal: International Journal of Modern Physics D Vol. 24, No. 11 (2015)
 1545002 (special issue "Composite dark matter")

url: http://arxiv.org/pdf/1510.01351v1.pdf

Abstract: We address the question of regular primordial black holes with de Sitter interior, their remnants and gravitational vacuum solitons G-lumps as heavy dark matter candidates providing signatures for inhomogeneity of early universe, which is severely constrained by the condition that the contribution of these objects in the modern density does not exceed the total density of dark matter. Primordial black holes and their remnants seem to be most elusive among dark matter candidates. However, we reveal a nontrivial property of compact objects with de Sitter interior to induce proton decay or decay of neutrons in neutron stars. The point is that they can form graviatoms, binding electrically charged particles. Their observational signatures as dark matter candidates provide also signatures for inhomogeneity of the early universe. In graviatoms, the cross-section of the induced proton decay is strongly enhanced, what provides the possibility of their experimental searches. We predict proton decay paths induced by graviatoms in the matter as an observational signature for heavy dark matter searches at the IceCUBE experiment.

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The first galaxies: simulating their feedback-regulated assembly

Published Paper #: 454

Authors:, Myoungwon Jeon, Volker Bromm, Andreas H. Pawlik, Milos Milosavljevic,

Journal: MNRAS, 452, 1152, 2015

url: http://arxiv.org/pdf/1501.01002v2.pdf

Abstract: We investigate the formation of a galaxy reaching a virial mass of $~ 10^8$ solar mass at $z=10$ by carrying out a zoomed radiation-hydrodynamical cosmological simulation. This simulation traces Population~III (Pop~III) star formation, characterized by a modestly top-heavy initial mass function (IMF), and considers stellar feedback such as photoionization heating from Pop III and Population~II (Pop~II) stars, mechanical and chemical feedback from supernovae (SNe), and X-ray feedback from accreting black holes (BHs) and high-mass X-ray binaries (HMXBs). We self-consistently impose a transition in star formation mode from top-heavy Pop III to low-mass Pop~II, and find that the star formation rate in the computational box is dominated by Pop~III until $z=13$, and by Pop~II thereafter. The simulated galaxy experiences bursty star formation, with a substantially reduced gas content due to photoionization heating from Pop~III and Pop~II stars, together with SN feedback. All the gas within the simulated galaxy is metal-enriched above $10^{-5}$ solar, such that there are no remaining pockets of primordial gas. The simulated galaxy has an estimated observed flux of $~10^{-3} nJy$, which is too low to be detected by the James Webb Space Telescope (JWST) without strong lensing amplification. We also show that our simulated galaxy is similar in terms of stellar mass to Segue 2, the least luminous dwarf known in the Local Group.

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Streched String with Self-Interaction at the Hagedorn Point: Spatial   Sizes and Black Hole

Published Paper #: 453

Authors:, Yachao Qian, Ismail Zahed,

Journal: Phys. Rev. D 92, 105001 (2015)

url: http://arxiv.org/pdf/1508.03760v1.pdf

Abstract: We analyze the length, mass and spatial distribution of a discretized transverse string in $D_\perp$ dimensions with fixed end-points near its Hagedorn temperature. We suggest that such a string may dominate the (holographic) Pomeron kinematics for dipole-dipole scattering at intermediate and small impact parameters. Attractive self-string interactions cause the transverse string size to contract away from its diffusive size, a mechanism reminiscent of the string-black-hole transmutation. The string shows sizable asymmetries in the transverse plane that translate to primordial azimuthal asymmetries in the stringy particle production in the Pomeron kinematics for current pp and pA collisions at collider energies.

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GAPS - Dark matter search with low-energy cosmic-ray antideuterons and   antiprotons

Published Paper #: 452

Authors:, P. von Doetinchem, T. Aramaki, S. Boggs, H. Fuke, C. J. Hailey, S. I. Mognet, R. A. Ong, K. Perez, J. Zweerink,

Journal: PoS (ICRC 2015) 1219

url: http://arxiv.org/pdf/1507.02717v2.pdf

Abstract: The GAPS experiment is foreseen to carry out a dark matter search by measuring low-energy cosmic-ray antideuterons and antiprotons with a novel detection approach. It will provide a new avenue to access a wide range of different dark matter models and masses from about 10GeV to 1TeV. The theoretically predicted antideuteron flux resulting from secondary interactions of primary cosmic rays is very low. Well-motivated theories beyond the Standard Model contain viable dark matter candidates, which could lead to a significant enhancement of the antideuteron flux due to annihilation or decay of dark matter particles. This flux contribution is believed to be especially large at low energies, which leads to a high discovery potential for GAPS. The GAPS low-energy antiproton search will provide some of the most stringent constraints on ~30GeV dark matter, will provide the best limits on primordial black hole evaporation on galactic length scales, and explore new discovery space in cosmic-ray physics.   GAPS is designed to achieve its goals via long duration balloon flights at high altitude in Antarctica. The detector itself will consist of 10 planes of Si(Li) solid state detectors and a surrounding time-of-flight system. Antideuterons and antiprotons will be slowed down in the Si(Li) material, replace a shell electron and form an excited exotic atom. The atom will be deexcited by characteristic X-ray transitions and will end its life by the formation of an annihilation pion/proton star. This unique event structure will deliver a nearly background free detection possibility.

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A Density Spike on Astrophysical Scales from an N-Field Waterfall   Transition

Published Paper #: 451

Authors:, Illan F. Halpern, Mark P. Hertzberg, Matthew A. Joss, Evangelos I. Sfakianakis,

Journal: Phys. Lett. B 748 (2015) 132-143

url: http://arxiv.org/pdf/1410.1878v3.pdf

Abstract: Hybrid inflation models are especially interesting as they lead to a spike in the density power spectrum on small scales, compared to the CMB, while also satisfying current bounds on tensor modes. Here we study hybrid inflation with $N$ waterfall fields sharing a global $SO(N)$ symmetry. The inclusion of many waterfall fields has the obvious advantage of avoiding topologically stable defects for $N>3$. We find that it also has another advantage: it is easier to engineer models that can simultaneously (i) be compatible with constraints on the primordial spectral index, which tends to otherwise disfavor hybrid models, and (ii) produce a spike on astrophysically large length scales. The latter may have significant consequences, possibly seeding the formation of astrophysically large black holes. We calculate correlation functions of the time-delay, a measure of density perturbations, produced by the waterfall fields, as a convergent power series in both $1/N$ and the field's correlation function $\Delta(x)$. We show that for large $N$, the two-point function is $<\delta t({\bf x})\,\delta t({\bf 0})>\,\propto\Delta^2(|{\bf x}|)/N$ and the three-point function is $<\delta t({\bf x})\,\delta t({\bf y})\,\delta t({\bf 0})>\,\propto\Delta(|{\bf x}-{\bf y}|)\Delta(|{\bf x}|)\Delta(|{\bf y}|)/N^2$. In accordance with the central limit theorem, the density perturbations on the scale of the spike are Gaussian for large $N$ and non-Gaussian for small $N$.

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Primordial black holes as biased tracers

Published Paper #: 450

Authors:, Yuichiro Tada, Shuichiro Yokoyama,

Journal: Phys. Rev. D 91, 123534 (2015)

url: http://arxiv.org/pdf/1502.01124v2.pdf

Abstract: Primordial black holes (PBHs) are theoretical black holes which may be formed during the radiation dominant era and, basically, caused by the gravitational collapse of radiational overdensities. It has been well known that in the context of the structure formation in our Universe such collapsed objects, e.g., halos/galaxies, could be considered as bias tracers of underlying matter fluctuations and the halo/galaxy bias has been studied well. Employing a peak-background split picture which is known to be a useful tool to discuss the halo bias, we consider the large scale clustering behavior of the PBH and propose an almost mass-independent constraint to the scenario that dark matters (DMs) consist of PBHs. We consider the case where the statistics of the primordial curvature perturbations is almost Gaussian, but with small local-type non-Gaussianity. If PBHs account for the DM abundance, such a large scale clustering of PBHs behaves as nothing but the matter isocurvature perturbation and constrained strictly by the observations of cosmic microwave backgrounds (CMB). From this constraint, we show that, in the case a certain single field causes both CMB temperature perturbations and PBH formations, the PBH-DM scenario is excluded even with quite small local-type non-Gaussianity, $|f_\mathrm{NL}|\sim\mathcal{O}(0.01)$, while we give the constraints to parameters in the case where the source field of PBHs is different from CMB perturbations.

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Kolmogorov complexity in the Milky Way and its reduction with warm dark   matter

Published Paper #: 449

Authors:, Mark C. Neyrinck,

Journal: MNRAS Letters 2015 452 (1): L26-L30

url: http://arxiv.org/pdf/1409.0057v2.pdf

Abstract: We discuss the Kolmogorov complexity of primordial patches that collapse to form galaxies like the Milky Way; this complexity quantifies the amount of initial data available to form the structure. We also speculate on how the quantity changes with time. Because of dark-matter and baryonic collapse processes, it likely decreases with time, i.e.\ information sinks dominate sources. But sources of new random information do exist; e.g., a central black hole with an accretion disk and jets could in principle broadcast small-scale quantum fluctuations over a substantial portion of a galaxy.   A speculative example of how this concept might be useful is in differentiating between warm (WDM) and cold (CDM) dark matter. With WDM, the initial patch that formed the Milky Way would have had few features, making the present high degree of structure a curiosity. The primordial patch would have had only several billion independent information-carrying `pixels' if the WDM particle had a mass of 1 keV. This number of `pixels' is much less than even the number of stars in the Milky Way. If the dark matter is proven to be warm, the high degree of structure in the Milky Way could have arisen in two ways: (1) from a high sensitivity to initial conditions, like an intricate fractal arising from a relatively simple computer code; or (2) from random information generated after the galaxy formed, i.e.\ not entirely deterministically from the initial conditions.

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Cosmological Probes for Supersymmetry

Published Paper #: 448

Authors:, Maxim Khlopov,

Journal: Symmetry 2015, 7, 815-842

url: http://arxiv.org/pdf/1505.08077v1.pdf

Abstract: The multi-parameter character of supersymmetric dark-matter models implies the combination of their experimental studies with astrophysical and cosmological probes. The physics of the early Universe provides nontrivial effects of non-equilibrium particles and primordial cosmological structures. Primordial black holes (PBHs) are a profound signature of such structures that may arise as a cosmological consequence of supersymmetric (SUSY) models. SUSY-based mechanisms of baryosynthesis can lead to the possibility of antimatter domains in a baryon asymmetric Universe. In the context of cosmoparticle physics, which studies the fundamental relationship of the micro- and macro-worlds, the development of SUSY illustrates the main principles of this approach, as the physical basis of the modern cosmology provides cross-disciplinary tests in physical and astronomical studies.

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Dark Matter Triggers of Supernovae

Published Paper #: 447

Authors:, Peter W. Graham, Surjeet Rajendran, Jaime Varela,

Journal: Phys. Rev. D 92, 063007 (2015)

url: http://arxiv.org/pdf/1505.04444v1.pdf

Abstract: The transit of primordial black holes through a white dwarf causes localized heating around the trajectory of the black hole through dynamical friction. For sufficiently massive black holes, this heat can initiate runaway thermonuclear fusion causing the white dwarf to explode as a supernova. The shape of the observed distribution of white dwarfs with masses up to $1.25 M_{\odot}$ rules out primordial black holes with masses $\sim 10^{19}$ gm - $10^{20}$ gm as a dominant constituent of the local dark matter density. Black holes with masses as large as $10^{24}$ gm will be excluded if recent observations by the NuStar collaboration of a population of white dwarfs near the galactic center are confirmed. Black holes in the mass range $10^{20}$ gm - $10^{22}$ gm are also constrained by the observed supernova rate, though these bounds are subject to astrophysical uncertainties. These bounds can be further strengthened through measurements of white dwarf binaries in gravitational wave observatories. The mechanism proposed in this paper can constrain a variety of other dark matter scenarios such as Q balls, annihilation/collision of large composite states of dark matter and models of dark matter where the accretion of dark matter leads to the formation of compact cores within the star. White dwarfs, with their astronomical lifetimes and sizes, can thus act as large space-time volume detectors enabling a unique probe of the properties of dark matter, especially of dark matter candidates that have low number density. This mechanism also raises the intriguing possibility that a class of supernova may be triggered through rare events induced by dark matter rather than the conventional mechanism of accreting white dwarfs that explode upon reaching the Chandrasekhar mass.

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Cosmological long-wavelength solutions and primordial black hole   formation

Published Paper #: 446

Authors:, Tomohiro Harada, Chul-Moon Yoo, Tomohiro Nakama, Yasutaka Koga,

Journal: Phys. Rev. D 91, 084057 (2015)

url: http://arxiv.org/pdf/1503.03934v2.pdf

Abstract: We construct cosmological long-wavelength solutions without symmetry in general gauge conditions compatible with the long-wavelength scheme. We then specify the relationship among the solutions in different time slicings. Applying this general framework to spherical symmetry, we derive the correspondence relation between long-wavelength solutions in the constant mean curvature slicing with conformally flat spatial coordinates and asymptotic quasihomogeneous solutions in the comoving gauge and compare the numerical results of PBH formation in these two different approaches. To discuss the PBH formation, it is convenient and conventional to use $\tilde{\delta}_{c}$, the value which the averaged density perturbation at threshold in the comoving slicing would take at horizon entry in the lowest-order long-wavelength expansion. We numerically find that within compensated models, the sharper the transition from the overdense region to the FRW universe is, the larger the $\tilde{\delta}_{c}$ becomes. We suggest that, for the equation of state $p=(\Gamma-1)\rho$, we can apply the analytic formulas for the minimum $\tilde{\delta}_{c, {\rm min}}\simeq [3\Gamma/(3\Gamma+2)]\sin^{2}\left[\pi\sqrt{\Gamma-1}/(3\Gamma-2)\right]$ and the maximum $\tilde{\delta}_{c, {\rm max}}\simeq 3\Gamma/(3\Gamma+2)$. As for the threshold peak value of the curvature variable $\psi_{0,c}$, we find that the sharper the transition is, the smaller the $\psi_{0,c}$ becomes. We analytically explain this feature. Using simplified models, we also analytically deduce an environmental effect that $\psi_{0,c}$ can be significantly larger (smaller) if the underlying density perturbation of much longer wavelength is positive (negative).

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The long-short wavelength mode coupling tightens primordial black hole   constraints

Published Paper #: 445

Authors:, Sam Young, Christian T. Byrnes,

Journal: Phys. Rev. D 91, 083521 (2015)

url: http://arxiv.org/pdf/1411.4620v2.pdf

Abstract: The effects of non-gaussianity on the constraints on the primordial curvature perturbation power spectrum from primordial black holes (PBHs) are considered. We extend previous analyses to include the effects of coupling between the modes of the horizon scale at the time the PBH forms and super-horizon modes. We consider terms of up to third order in the Gaussian perturbation. For the weakest constraints on the abundance of PBHs in the early universe (corresponding to a fractional energy density of PBHs of $10^{-5}$ at the time of formation), in the case of gaussian perturbations, constraints on the power spectrum are $\mathcal{P}_{\zeta}<0.05$ but can significantly tighter when even a small amount of non-gaussianity is considered, to $\mathcal{P}_{\zeta}<0.01$, and become approximately $\mathcal{P}_{\zeta}<0.003$ in more special cases. Surprisingly, even when there is negative skew (which naively would suggest fewer areas of high density, leading to weaker constraints), we find that the constraints on the power spectrum become tighter than the purely gaussian case - in strong contrast with previous results. We find that the constraints are highly sensitive to both the non-gaussianity parameters as well as the amplitude of super-horizon perturbations.

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Signatures of non-gaussianity in the isocurvature modes of primordial   black hole dark matter

Published Paper #: 444

Authors:, Sam Young, Christian T. Byrnes,

Journal: JCAP 1504 (2015) 04, 034

url: http://arxiv.org/pdf/1503.01505v2.pdf

Abstract: Primordial black holes (PBHs) are black holes which may have formed very early on during the radiation dominated era in the early universe. We present here a method by which the large scale perturbations in the density of primordial black holes may be used to place tight constraints on non-gaussianity if PBHs account for dark matter (DM). The presence of local-type non-gaussianity is known to have a significant effect on the abundance of primordial black holes, and modal coupling from the observed CMB scale modes can significantly alter the number density of PBHs that form within different regions of the universe, which appear as DM isocurvature modes. Using the recent \emph{Planck} constraints on isocurvature perturbations, we show that PBHs are excluded as DM candidates for even very small local-type non-gaussianity, $|f_{NL}|\approx0.001$ and remarkably the constraint on $g_{NL}$ is almost as strong. Even small non-gaussianity is excluded if DM is composed of PBHs. If local non-Gaussianity is ever detected on CMB scales, the constraints on the fraction of the universe collapsing into PBHs (which are massive enough to have not yet evaporated) will become much tighter.

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Calculating the mass spectrum of primordial black holes

Published Paper #: 443

Authors:, Sam Young, Christian T. Byrnes, Misao Sasaki,

Journal: JCAP 1407 (2014) 045

url: http://arxiv.org/pdf/1405.7023v4.pdf

Abstract: We reinspect the calculation for the mass fraction of primordial black holes (PBHs) which are formed from primordial perturbations, finding that performing the calculation using the comoving curvature perturbation $\mathcal{R}_{c}$ in the standard way vastly overestimates the number of PBHs, by many orders of magnitude. This is because PBHs form shortly after horizon entry, meaning modes significantly larger than the PBH are unobservable and should not affect whether a PBH forms or not - this important effect is not taken into account by smoothing the distribution in the standard fashion. We discuss alternative methods and argue that the density contrast, $\Delta$, should be used instead as super-horizon modes are damped by a factor $k^{2}$. We make a comparison between using a Press-Schechter approach and peaks theory, finding that the two are in close agreement in the region of interest. We also investigate the effect of varying the spectral index, and the running of the spectral index, on the abundance of primordial black holes.

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Primordial black holes with mass $10^{16}-10^{17}$ g and reionization of   the Universe

Published Paper #: 442

Authors:, K. M. Belotsky, A. A. Kirillov,

Journal: Journal of Cosmology and Astroparticle Physics 01 (2015) 041

url: http://arxiv.org/pdf/1409.8601v3.pdf

Abstract: Primordial black holes (PBHs) with mass $10^{16}-10^{17}$ g almost escape constraints from observations so could essentially contribute to dark matter density. Hawking evaporation of such PBHs produces with a steady rate $\gamma$- and $e^{\pm}$-radiations in MeV energy range, which can be absorbed by ordinary matter. Simplified estimates show that a small fraction of evaporated energy had to be absorbed by baryonic matter what can turn out to be enough to heat the matter so it is fully ionized at the redshift $z\sim 5... 10$. The result is found to be close to a borderline case where the effect appears, what makes it sensitive to the approximation used. In our approximation, degree of gas ionization reaches 50-100% by $z\sim 5$ for PBH mass $(3...7)\times 10^{16}$ g with their abundance corresponding to the upper limit.

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Efficient electroweak baryogenesis by black holes

Published Paper #: 441

Authors:, Georgios Aliferis, Georgios Kofinas, Vasilios Zarikas,

Journal: Phys. Rev. D 91, 045002 (2015)

url: http://arxiv.org/pdf/1406.6215v2.pdf

Abstract: A novel cosmological scenario, capable to generate the observed baryon number at the electroweak scale for very small CP violating angles, is presented. The proposed mechanism can be applied in conventional FRW cosmology, but becomes extremely efficient due to accretion in the context of early cosmic expansion with high energy modifications. Assuming that our universe is a Randall-Sundrum brane, baryon asymmetry can easily be produced by Hawking radiation of very small primordial black holes. The Hawking radiation reheats a spherical region around every black hole to a high temperature and the electroweak symmetry is restored there. A domain wall is formed separating the region with the symmetric vacuum from the asymmetric region where electroweak baryogenesis takes place. First order phase transition is not needed. The black holes's lifetime is prolonged due to accretion, resulting to strong efficiency of the baryon producing mechanism. The allowed by the mechanism black hole mass range includes masses that are energetically favoured to be produced from interactions around the higher dimensional Planck scale.

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Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and   the seeds of Galaxies

Published Paper #: 440

Authors:, Sébastien Clesse, Juan García-Bellido,

Journal: Phys. Rev. D 92, 023524 (2015)

url: http://arxiv.org/pdf/1501.07565v1.pdf

Abstract: In this paper we present a new scenario where massive Primordial Black Holes (PBH) are produced from the collapse of large curvature perturbations generated during a mild waterfall phase of hybrid inflation. We determine the values of the inflaton potential parameters leading to a PBH mass spectrum peaking on planetary-like masses at matter-radiation equality and producing abundances comparable to those of Dark Matter today, while the matter power spectrum on scales probed by CMB anisotropies agrees with Planck data. These PBH could have acquired large stellar masses today, via merging, and the model passes both the constraints from CMB distortions and micro-lensing. This scenario is supported by Chandra observations of numerous BH candidates in the central region of Andromeda. Moreover, the tail of the PBH mass distribution could be responsible for the seeds of supermassive black holes at the center of galaxies, as well as for ultra-luminous X-rays sources. We find that our effective hybrid potential can originate e.g. from D-term inflation with a Fayet-Iliopoulos term of the order of the Planck scale but sub-planckian values of the inflaton field. Finally, we discuss the implications of quantum diffusion at the instability point of the potential, able to generate a swiss-cheese like structure of the Universe, eventually leading to apparent accelerated cosmic expansion.

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Observational Limits on Gauss-Bonnet and Randall-Sundrum Gravities

Published Paper #: 439

Authors:, S. O. Alexeyev, K. A. Rannu, P. I. Dyadina, B. N. Latosh, S. G. Turyshev,

Journal: JETP 147 (6), 1120-1127 (2015)

url: http://arxiv.org/pdf/1501.04217v1.pdf

Abstract: We discuss the possibilities of experimental search for new physics predicted by the Gauss-Bonnet and the Randall-Sundrum theories of gravity. The effective four-dimensional spherically-symmetrical solutions of these theories are analyzed. We consider these solutions in the weak-field limit and in the process of the primordial black holes evaporation. We show that the predictions of discussed models are the same as of General Relativity. So, current experiments are not applicable for such search therefore different methods of observation and higher accuracy are required.

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Simulating the growth of Intermediate Mass Black Holes

Published Paper #: 438

Authors:, Fabio Pacucci, Andrea Ferrara,

Journal: Monthly Notices of the Royal Astronomical Society 2015 448 (2):
 104-118

url: http://arxiv.org/pdf/1501.00989v1.pdf

Abstract: Theoretical models predict that a population of Intermediate Mass Black Holes (IMBHs) of mass $M_\bullet \approx 10^{4-5} \, \mathrm{M_{\odot}}$ might form at high ($z > 10$) redshift by different processes. Such objects would represent the seeds out of which $z > 6$ Super-Massive Black Holes (SMBHs) grow. We numerically investigate the radiation-hydrodynamic evolution governing the growth of such seeds via accretion of primordial gas within their parent dark matter halo of virial temperature $T_{vir} \sim 10^4 \, \mathrm{K}$. We find that the accretion onto a Direct Collapse Black Hole (DCBH) of initial mass $M_0=10^5 \, \mathrm{M_{\odot}}$ occurs at an average rate $\dot{M}_{\bullet} \simeq 1.35 \, \dot{M}_{Edd} \simeq 0.1 \, \mathrm{M_{\odot} \, yr^{-1}}$, is intermittent (duty-cycle $ < 50\%$) and lasts $\approx 142 \, \mathrm{Myr}$; the system emits on average at super-Eddington luminosities, progressively becoming more luminous as the density of the inner mass shells, directly feeding the central object, increases. Finally, when $\approx 90\%$ of the gas mass has been accreted (in spite of an average super-Eddington emission) onto the black hole, whose final mass is $\sim 7 \times 10^6 \, \mathrm{M_{\odot}}$, the remaining gas is ejected from the halo due to a powerful radiation burst releasing a peak luminosity $L_{peak}\sim 3\times 10^{45} \, \mathrm{erg \, s^{-1}}$. The IMBH is Compton-thick during most of the evolution, reaching a column density $N_H \sim 10^{25} \, \mathrm{cm^{-2}}$ in the late stages of the simulation. We briefly discuss the observational implications of the model.

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Baryogenesis from Hawking Radiation

Published Paper #: 437

Authors:, Anson Hook,

Journal: Phys. Rev. D 90, 083535 (2014)

url: http://arxiv.org/pdf/1404.0113v3.pdf

Abstract: We show that in the presence of a chemical potential, black hole evaporation generates baryon number. If the inflaton or Ricci scalar is derivatively coupled to the B-L current, the expansion of the universe acts as a chemical potential and splits the energy levels of particles and their anti-particles. The asymmetric Hawking radiation of primordial black holes can thus be used to generate a B-L asymmetry. If dark matter is produced by the same mechanism, the coincidence between the mass density of visible and dark matter can be naturally explained.

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Constraints on the primordial power spectrum of small scales using the   neutrino signals from the dark matter decay

Published Paper #: 436

Authors:, Yupeng Yang,

Journal: International Journal of Modern Physics A, Vol. 29, No. 32 (2014)
 1450194 (10 pages)

url: http://arxiv.org/pdf/1501.00789v1.pdf

Abstract: Many inflation theories predict that the primordial power spectrum is scale invariant. The amplitude of the power spectrum can be constrained by different observations such as the cosmic microwave background (CMB), Lyman-$\alpha$, large-scale structures and primordial black holes (PBHs). Although the constraints from the CMB are robust, the corresponding scales are very large ($10^{-4}<k<1 \mathrm{Mpc^{-1}}$). For small scales ($k > 1 \mathrm{Mpc^{-1}}$), the research on the PBHs provides much weaker limits. Recently, ultracompact dark matter minihalos (UCMHs) was proposed and it was found that they could be used to constraint the small-scale primordial power spectrum. The limits obtained by the research on the UCMHs are much better than that of PBHs. Most of previous works focus on the dark matter annihilation within the UCMHs, but if the dark matter particles do not annihilate the decay is another important issue. In previous work~\cite{EPL}, we investigated the gamma-ray flux from the UCMHs due to the dark matter decay. In addition to these flux, the neutrinos are usually produced going with the gamma-ray photons especially for the lepton channels. In this work, we studied the neutrino flux from the UCMHs due to the dark matter decay. Finally, we got the constraints on the amplitude of primordial power spectrum of small scales.

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Formation of massive protostars in atomic cooling haloes

Published Paper #: 435

Authors:, Fernando Becerra, Thomas H. Greif, Volker Springel, Lars Hernquist,

Journal: MNRAS, 446, 2380 (2015)

url: http://arxiv.org/pdf/1409.3572v2.pdf

Abstract: We present the highest-resolution three-dimensional simulation to date of the collapse of an atomic cooling halo in the early Universe. We use the moving-mesh code arepo with the primordial chemistry module introduced in Greif (2014), which evolves the chemical and thermal rate equations for over more than 20 orders of magnitude in density. Molecular hydrogen cooling is suppressed by a strong Lyman-Werner background, which facilitates the near-isothermal collapse of the gas at a temperature of about $10^4\,$K. Once the central gas cloud becomes optically thick to continuum emission, it settles into a Keplerian disc around the primary protostar. The initial mass of the protostar is about $0.1\,{\rm M}_\odot$, which is an order of magnitude higher than in minihaloes that cool via molecular hydrogen. The high accretion rate and efficient cooling of the gas catalyse the fragmentation of the disc into a small protostellar system with 5-10 members. After about 12 yr, strong gravitational interactions disrupt the disc and temporarily eject the primary protostar from the centre of the cloud. By the end of the simulation, a secondary clump has collapsed at a distance of $\simeq 150\,$au from the primary clump. If this clump undergoes a similar evolution as the first, the central gas cloud may evolve into a wide binary system. High accretion rates of both the primary and secondary clumps suggest that fragmentation is not a significant barrier for forming at least one massive black hole seed.

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Effects of turbulence and rotation on protostar formation as a precursor   to seed black holes

Published Paper #: 434

Authors:, C. Van Borm, S. Bovino, M. A. Latif, D. R. G. Schleicher, M. Spaans, T. Grassi,

Journal: A&A 572, A22 (2014)

url: http://arxiv.org/pdf/1408.1253v2.pdf

Abstract: Context. The seeds of the first supermassive black holes may have resulted from the direct collapse of hot primordial gas in $\gtrsim 10^4$ K haloes, forming a supermassive or quasistar as an intermediate stage.   Aims. We explore the formation of a protostar resulting from the collapse of primordial gas in the presence of a strong Lyman-Werner radiation background. Particularly, we investigate the impact of turbulence and rotation on the fragmentation behaviour of the gas cloud. We accomplish this goal by varying the initial turbulent and rotational velocities.   Methods. We performed 3D adaptive mesh refinement simulations with a resolution of 64 cells per Jeans length using the ENZO code, simulating the formation of a protostar up to unprecedentedly high central densities of $10^{21}$ cm$^{-3}$, and spatial scales of a few solar radii. To achieve this goal, we employed the KROME package to improve modelling of the chemical and thermal processes.   Results. We find that the physical properties of the simulated gas clouds become similar on small scales, irrespective of the initial amount of turbulence and rotation. After the highest level of refinement was reached, the simulations have been evolved for an additional ~5 freefall times. A single bound clump with a radius of $2 \times 10^{-2}$ AU and a mass of ~$7 \times 10^{-2}$ M$_{\odot}$ is formed at the end of each simulation, marking the onset of protostar formation. No strong fragmentation is observed by the end of the simulations, regardless of the initial amount of turbulence or rotation, and high accretion rates of a few solar masses per year are found.   Conclusions. Given such high accretion rates, a quasistar of $10^5$ M$_{\odot}$ is expected to form within $10^5$ years.

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Axion inflation with gauge field production and primordial black holes

Published Paper #: 433

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys. Rev. D 90, 103501 (2014)

url: http://arxiv.org/pdf/1312.7435v2.pdf

Abstract: We study the process of primordial black hole (PBH) formation at the beginning of radiation era for the cosmological scenario in which the inflaton is a pseudo-Nambu-Goldstone boson (axion) and there is a coupling of the inflaton with some gauge field. In this model inflation is accompanied by the gauge quanta production and a strong rise of the curvature power spectrum amplitude at small scales (along with non-Gaussianity) is predicted. We show that data on PBH searches can be used for a derivation of essential constraints on the model parameters in such an axion inflation scenario. We compare our numerical results with the similar results published earlier, in the work by Linde et al.

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Testing scenarios of primordial black holes being the seeds of   supermassive black holes by ultracompact minihalos and CMB $μ$-distortions

Published Paper #: 432

Authors:, Kazunori Kohri, Tomohiro Nakama, Teruaki Suyama,

Journal: Phys. Rev. D 90: 083514, 2014

url: http://arxiv.org/pdf/1405.5999v2.pdf

Abstract: Supermassive black holes and intermediate mass black holes are believed to exist in the Universe. There is no established astrophysical explanation for their origin and considerations have been made in the literature that those massive black holes (MBHs) may be primordial black holes (PBHs), black holes which are formed in the early universe (well before the matter-radiation equality) due to the direct collapse of primordial overdensities. This paper aims at discussing the possibility of excluding the PBH scenario as the origin of the MBHs. We first revisit the constraints on PBHs obtained from the CMB distortion that the seed density perturbation causes. By adopting a recent computation of the CMB distortion sourced by the seed density perturbation and the stronger constraint on the CMB distortion set by the COBE/FIRAS experiment used in the literature, we find that PBHs in the mass range $6\times 10^4~M_\odot \sim 5 \times 10^{13}~M_\odot$ are excluded. Since PBHs lighter than $6 \times 10^4~M_\odot$ are not excluded from the non-observation of the CMB distortion, we propose a new method which can potentially exclude smaller PBHs as well. Based on the observation that large density perturbations required to create PBHs also result in the copious production of ultracompact minihalos (UCMHs), compact dark matter halos formed at around the recombination, we show that weakly interacting massive particles (WIMPs) as dark matter annihilate efficiently inside UCMHs to yield cosmic rays far exceeding the observed flux. Our bound gives severe restriction on the compatibility between the particle physics models for WIMPs and the PBH scenario as the explanation of MBHs.

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Adiabatic contraction revisited: implications for primordial black holes

Published Paper #: 431

Authors:, Fabio Capela, Maxim Pshirkov, Peter Tinyakov,

Journal: Phys. Rev. D 90, 083507 (2014)

url: http://arxiv.org/pdf/1403.7098v2.pdf

Abstract: We simulate the adiabatic contraction of a dark matter (DM) distribution during the process of the star formation, paying particular attention to the phase space distribution of the DM particles after the contraction. Assuming the initial uniform density and Maxwellian distribution of DM velocities, we find that the number $n(r)$ of DM particles within the radius $r$ scales like $n(r) \propto r^{1.5}$, leading to the DM density profile $\rho\propto r^{-1.5}$, in agreement with the Liouville theorem and previous numerical studies. At the same time, the number of DM particles $\nu(r)$ with periastra smaller than $r$ is parametrically larger, $\nu(r) \propto r$, implying that many particles contributing at any given moment into the density $\rho(r)$ at small $r$ have very elongated orbits and spend most of their time at distances larger than $r$. This has implications for the capture of DM by stars in the process of their formation. As a concrete example we consider the case of primordial black holes (PBH). We show that accounting for very eccentric orbits boosts the amount of captured PBH by a factor of up to $2\times 10^3$ depending on the PBH mass, improving correspondingly the previously derived constraints on the PBH abundance.

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Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating   Primordial Black Holes

Published Paper #: 430

Authors:, A. A. Abdo, A. U. Abeysekara, R. Alfaro, B. T. Allen, C. Alvarez, J. D. Álvarez, R. Arceo, J. C. Arteaga-Velázquez, T. Aune, H. A. Ayala Solares, A. S. Barber, B. M. Baughman, N. Bautista-Elivar, J. Becerra Gonzalez, E. Belmont, S. Y. BenZvi, D. Berley, M. Bonilla Rosales, J. Braun, R. A. Caballero-Lopez, K. S. Caballero-Mora, A. Carramiñana, M. Castillo, C. Chen, G. E. Christopher, U. Cotti, J. Cotzomi, E. de la Fuente, C. De León, T. DeYoung, R. Diaz Hernandez, L. Diaz-Cruz, J. C. Díaz-Vélez, B. L. Dingus, M. A. DuVernois, R. W. Ellsworth, D. W. Fiorino, N. Fraija, A. Galindo, F. Garfias, M. M. González, J. A. Goodman, V. Grabski, M. Gussert, Z. Hampel-Arias, J. P. Harding, E. Hays, C. M. Hoffman, C. M. Hui, P. Hüntemeyer, A. Imran, A. Iriarte, P. Karn, D. Kieda, B. E. Kolterman, G. J. Kunde, A. Lara, R. J. Lauer, W. H. Lee, D. Lennarz, H. León Vargas, E. C. Linares, J. T. Linnemann, M. Longo, R. Luna-GarcIa, J. H. MacGibbon, A. Marinelli, S. S. Marinelli, H. Martinez, O. Martinez, J. Martínez-Castro, J. A. J. Matthews, J. McEnery, E. Mendoza Torres, A. I. Mincer, P. Miranda-Romagnoli, E. Moreno, T. Morgan, M. Mostafá, L. Nellen, P. Nemethy, M. Newbold, R. Noriega-Papaqui, T. Oceguera-Becerra, B. Patricelli, R. Pelayo, E. G. Pérez-Pérez, J. Pretz, C. Rivière, D. Rosa-González, J. Ryan, H. Salazar, F. Salesa, A. Sandoval, P. M. Saz Parkinson, M. Schneider, A. Shoup, S. Silich, G. Sinnis, A. J. Smith, D. Stump, K. Sparks Woodle, R. W. Springer, I. Taboada, P. A. Toale, K. Tollefson, I. Torres, T. N. Ukwatta, V. Vasileiou, L. Villaseñor, G. P. Walker, T. Weisgarber, S. Westerhoff, D. A. Williams, I. G. Wisher, J. Wood, G. B. Yodh, P. W. Younk, D. Zaborov, A. Zepeda, H. Zhou,

Journal: Astroparticle Physics, Volume 64, p. 4-12. 2015

url: http://arxiv.org/pdf/1407.1686v2.pdf

Abstract: Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of ~5.0 x 10^14 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.

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Signatures of primordial black hole dark matter

Published Paper #: 429

Authors:, K. M. Belotsky, A. D. Dmitriev, E. A. Esipova, V. A. Gani, A. V. Grobov, M. Yu. Khlopov, A. A. Kirillov, S. G. Rubin, I. V. Svadkovsky,

Journal: Mod. Phys. Lett. A 29 (2014) 1440005

url: http://arxiv.org/pdf/1410.0203v1.pdf

Abstract: The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro world and mechanisms of its symmetry breaking. In the early Universe heavy metastable particles can dominate, leaving primordial black holes (PBHs) after their decay, as well as the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which massive black holes and/or their clusters can originate. PBHs can be formed in such transitions within a narrow interval of masses about $10^{17}$g and, avoiding severe observational constraints on PBHs, can be a candidate for the dominant form of dark matter. PBHs in this range of mass can give solution of the problem of reionization in the Universe at the redshift $z\sim 5... 10$. Clusters of massive PBHs can serve as a nonlinear seeds for galaxy formation, while PBHs evaporating in such clusters can provide an interesting interpretation for the observations of point-like gamma-ray sources. Analysis of possible PBH signatures represents a universal probe for super-high energy physics in the early Universe in studies of indirect effects of the dark matter.

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Fast Radio Bursts and White Hole Signals

Published Paper #: 428

Authors:, Aurélien Barrau, Carlo Rovelli, Francesca Vidotto,

Journal: Phys. Rev. D 90, 127503 (2014)

url: http://arxiv.org/pdf/1409.4031v3.pdf

Abstract: We estimate the size of a primordial black hole exploding today via a white hole transition, and the power in the resulting explosion, using a simple model. We point out that Fast Radio Bursts, strong signals with millisecond duration, probably extragalactic and having unknown source, have wavelength not far from the expected size of the exploding hole. We also discuss the possible higher energy components of the signal.

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On tidal capture of primordial black holes by neutron stars

Published Paper #: 427

Authors:, Guillaume Defillon, Etienne Granet, Petr Tinyakov, Michel H. G. Tytgat,

Journal: Phys. Rev. D 90, 103522 (2014)

url: http://arxiv.org/pdf/1409.0469v1.pdf

Abstract: The fraction of primordial black holes (PBHs) of masses $10^{17} - 10^{26}$ g in the total amount of dark matter may be constrained by considering their capture by neutron stars (NSs), which leads to the rapid destruction of the latter. The constraints depend crucially on the capture rate which, in turn, is determined by the energy loss by a PBH passing through a NS. Two alternative approaches to estimate the energy loss have been used in the literature: the one based on the dynamical friction mechanism, and another on tidal deformations of the NS by the PBH. The second mechanism was claimed to be more efficient by several orders of magnitude due to the excitation of particular oscillation modes reminiscent of the surface waves. We address this disagreement by considering a simple analytically solvable model that consists of a flat incompressible fluid in an external gravitational field. In this model, we calculate the energy loss by a PBH traversing the fluid surface. We find that the excitation of modes with the propagation velocity smaller than that of PBH is suppressed, which implies that in a realistic situation of a supersonic PBH the large contributions from the surface waves are absent and the above two approaches lead to consistent expressions for the energy loss.

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The double formation of primordial black holes

Published Paper #: 426

Authors:, Tomohiro Nakama,

Journal: JCAP10(2014)040

url: http://arxiv.org/pdf/1408.0955v3.pdf

Abstract: Primordial black holes (PBHs) are a useful tool in cosmology to probe primordial inhomogeneities on small scales that reenter the Hubble radius during the radiation dominated epoch. In this paper, a phenomenon we call the double formation of PBHs, described below, is explored. Suppose there exists a highly perturbed region which will collapse to form a PBH after the horizon crossing of this region, and farther that this region is superposed on much larger region, which also collapses upon reentry. One then expects the collapse of the central smaller region at the time of the crossing of this region, followed by another collapse of the larger perturbation at the time of its respective crossing. The smaller PBH, formed earlier, should be swallowed in the second collapse leading to a single larger PBH as the final state. This paper reports the first direct numerical confirmation of such double PBH formation. Related to this, we also discuss the effects of high-frequency modes on the formation of PBHs.

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Reheating the Universe Once More: The Dissipation of Acoustic Waves as a   Novel Probe of Primordial Inhomogeneities on Even Smaller Scales

Published Paper #: 425

Authors:, Tomohiro Nakama, Teruaki Suyama, Jun'ichi Yokoyama,

Journal: Phys. Rev. Lett. 113, 061302 (2014)

url: http://arxiv.org/pdf/1403.5407v2.pdf

Abstract: We provide a simple but robust bound on the primordial curvature perturbation in the range $10^4 {\rm Mpc}^{-1} < k < 10^5 {\rm Mpc}^{-1}$, which has not been constrained so far unlike low wavenumber modes. Perturbations on these scales dissipate the energy of their acoustic oscillations by the Silk damping after primordial nucleosynthesis but before the redshift $z \sim 2 \times 10^6$ and reheat the photon bath without invoking CMB distortions. This {\it acoustic reheating} results in the decrease of the baryon-photon ratio. By combining independent measurements probing the nucleosynthesis era and around the recombination epoch, we find an upper bound on the amplitude of the curvature perturbation over the above wavenumber range as ${\cal P}_\zeta < 0.06$. Implications for super massive black holes are also discussed.

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Clearing the Brush: The Last Stand of Solo Small Field Inflation

Published Paper #: 424

Authors:, Joseph Bramante, Sean Downes, Landon Lehman, Adam Martin,

Journal: Phys. Rev. D 90, 023530 (2014)

url: http://arxiv.org/pdf/1405.7563v3.pdf

Abstract: By incorporating both the tensor-to-scalar ratio and the measured value of the spectral index, we set a bound on solo small field inflation of $\Delta \phi / m_{Pl} \geq 1.00 \sqrt{r/0.1}$. Unlike previous bounds which require monotonic $\epsilon_V,$ $|\eta_V| <1$, and 60 e-folds of inflation, the bound remains valid for non-monotonic $\epsilon_V$, $|\eta_V| \gtrsim 1$, and for inflation which occurs only over the 8 e-folds which have been observed on the cosmic microwave background. The negative value of the spectral index over the observed 8 e-folds is what makes the bound strong; we illustrate this by surveying single field models and finding that for $r \gtrsim 0.1$ and 8 e-folds of inflation, there is no simple potential which reproduces observed CMB perturbations and remains sub-Planckian. Models that are sub-Planckian after 8 e-folds must be patched together with a second epoch of inflation that fills out the remaining $\sim 50$ e-folds. This second, post-CMB epoch is characterized by extremely small $\epsilon_V$ and therefore an increasing scalar power spectrum. Using the fact that large power can overabundantly produce primordial black holes, we bound the maximum energy level of the second phase of inflation.

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Isotropic Expansion of Inhomogeneous Universe

Published Paper #: 423

Authors:, Wei-Jian Geng, H. Lu,

Journal: Phys. Rev. D 90, 083511 (2014)

url: http://arxiv.org/pdf/1407.0728v2.pdf

Abstract: We propose a cosmological model that describes isotropic expansion of inhomogeneous universe. The energy-momentum tensor that creates the spatial inhomogeneity may not affect the uniform expansion scaling factor $a(t)$ in the FLRW-like metrics. Such energy-momentum tensor may not be exotic; in fact any linear or non-linear $\sigma$-model has this feature. We show that the classical spatial inhomogeneity can be embedded in both inflation models and the traditional cosmological expansion by perfect fluid. The spatial inhomogeneity resembles the primordial quantum perturbation that was frozen in the co-moving frame. We obtain some exact inhomogeneous solutions with spherical or axial symmetries. We also show that some of our cosmological models can be viewed as the dynamical black hole formation.

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The primordial environment of super massive black holes: large scale   galaxy overdensities around $z\sim6$ QSOs with LBT

Published Paper #: 422

Authors:, L. Morselli, M. Mignoli, R. Gilli, C. Vignali, A. Comastri, E. Sani, N. Cappelluti, G. Zamorani, M. Brusa, S. Gallozzi, E. Vanzella,

Journal: A&A 568, A1 (2014)

url: http://arxiv.org/pdf/1406.3961v1.pdf

Abstract: We investigated the presence of galaxy overdensities around four $z\sim6$ QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep $r$-, $i$- and $z$- band imaging obtained with the wide-field ($\sim23'\times25'$) Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted color-color selections within the $i-z$ vs $r-z$ plane to identify samples of $i$-band dropouts at the QSO redshift and measure their relative abundance and spatial distribution in the four LBC fields, each covering $\sim8\times8$ physical Mpc at $z\sim6$. The same selection criteria were then applied to $z$-band selected sources in the $\sim$1 deg$^2$ Subaru-XMM Newton Deep Survey to derive the expected number of dropouts over a blank LBC-sized field ($\sim$0.14 deg$^2$). The four observed QSO fields host a number of candidates larger than what is expected in a blank field. By defining as $i$-band dropouts objects with $z_{AB}<25$, $i-z>1.4$ and undetected in the $r$-band, we found 16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg$^2$ blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, 2.5$\sigma$, respectively. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg$^2$ each, we find that high-z QSOs reside in overdense environments at the $3.7\sigma$ level. This is the first direct and unambiguous measurement of the large scale structures around $z\sim6$ QSOs. [shortened]

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Direct detection of Black Holes via electromagnetic radiation

Published Paper #: 421

Authors:, J. L. G. Sobrinho, P. Augusto,

Journal: Mon. Not. Roy. Astron. Soc. 441 (2), 2878-2884 (2014)

url: http://arxiv.org/pdf/1406.1785v1.pdf

Abstract: Many black hole (BH) candidates exist, ranging from supermassive ($\sim10^{6}$--$10^{10}$ M$_{\odot}$) to stellar masses ($\sim 1$--$100$ M$_{\odot}$), all of them identified by indirect processes. Although there are no known candidate BHs with sub-stellar masses, these might have been produced in the primordial Universe. BHs emit radiation composed of photons, gravitons and, later in their lifes, massive particles. We explored the detection of such BHs with present day masses from $10^{-22}$ M$_{\odot}$ to $10^{-11}$ M$_{\odot}$. We determined the maximum distances ($d$) at which the current best detectors should be placed in order to identify such isolated BHs. Broadly, we conclude that in the visible and ultraviolet BHs can be directly detected at $d\lesssim 10^7$ m while in the X-ray band the distances might reach $\sim10^8$ m (of the order of the Earth-Moon distance) and in the $\gamma$-ray band BHs might even be detected from as far as $\sim 0.1$ pc. Since these results give us realistic hopes of directly detecting BHs, we suggest the scrutiny of current and future space mission data to reach this goal.

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Thermal Tachyacoustic Cosmology

Published Paper #: 420

Authors:, Abhineet Agarwal, Niayesh Afshordi,

Journal: Phys. Rev. D 90, 043528 (2014)

url: http://arxiv.org/pdf/1406.0575v1.pdf

Abstract: An intriguing possibility that can address pathologies in both early universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. non-renormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. A concrete realization of this possibility for the early universe is the Tachyacoustic (or Speedy Sound) cosmology, which could also produce a scale-invariant spectrum for scalar cosmological perturbations. Here, we study Thermal Tachyacoustic Cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early universe, around the scale of Grand Unified Theories (GUT scale; $T\sim 10^{15}$ GeV), during which the speed of sound drops by $25$ orders of magnitude within a Hubble time, can fit current CMB observations. We further discuss how production of primordial black holes constrains the cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity leads to a lower limit on the amplitude of tensor modes ($r \gtrsim 10^{-3}$), that are detectable by CMBPol (and might have already been seen by the BICEP-Keck collaboration).

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Primordial black holes from temporally enhanced curvature perturbation

Published Paper #: 419

Authors:, Teruaki Suyama, Yi-Peng Wu, Jun'ichi Yokoyama,

Journal: Phys. Rev. D 90, 043514 (2014)

url: http://arxiv.org/pdf/1406.0249v1.pdf

Abstract: Scalar field with generalized kinetic interactions metamorphoses depending on its field value, ranging from cosmological constant to stiff matter. We show that such a scalar field can give rise to temporal enhancement of the curvature perturbation in the primordial Universe, leading to efficient production of primordial black holes while the enhancement persists. If the inflation energy scale is high, those mini-black holes evaporate by the Hawking radiation much before Big Bang nucleosynthesis and the effective reheating of the Universe is achieved by the black hole evaporation. Dominance of PBHs and the reheating by their evaporation modify the expansion history of the primordial Universe. This results in a characteristic feature of the spectrum of primordial tensor modes in the DECIGO frequency band, opening an interesting possibility of testing PBH reheating scenario by measuring the primordial tensor modes. If the inflation energy scale is low, the PBH mass can be much larger than the solar mass. In this case, PBH is an interesting candidate for seeds for supermassive black holes residing in present galaxies.

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The separate universe problem: 40 years on

Published Paper #: 418

Authors:, B. J. Carr, Tomohiro Harada,

Journal: Phys. Rev. D 91, 084048 (2015)

url: http://arxiv.org/pdf/1405.3624v1.pdf

Abstract: The claim that an overdense (positive curvature) region in the early universe cannot extend beyond some maximum scale and remain part of our universe, first made 40 years ago, has recently been questioned by Kopp et al. Their analysis is elucidating and demonstrates that one cannot constrain the form of primordial density perturbations using this argument. However, the notion of a separate-universe scale still applies and it places an important upper limit on the mass of primordial black holes forming at any epoch. We calculate this scale for equations of state of the form $p = k \rho c^2$ with $-1 <k < \infty$, refining earlier calculations on account of the Kopp et al. criticisms. For $-1/3 < k < \infty$, the scale is always of order the cosmological particle horizon size, with a numerical factor depending on $k$. This confirms the earlier claim that a primordial black hole cannot be much larger than the particle horizon at formation. For $-1 < k< -1/3$, as expected for some periods in the history of the universe, the situation changes radically, in that a sufficiently large positive-curvature region produces a baby universe rather than a black hole. There is still a separate-universe scale but the interpretation of these solutions requires care.

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Formation of subhorizon black holes from preheating

Published Paper #: 417

Authors:, E. Torres-Lomas, Juan Carlos Hidalgo, Karim A. Malik, L. Arturo Ureña-López,

Journal: Phys. Rev. D 89, 083008 (2014)

url: http://arxiv.org/pdf/1401.6960v2.pdf

Abstract: We study the production of primordial black holes (PBHs) during the preheating stage that follows a chaotic inflationary phase. The scalar fields present in the process are evolved numerically using a modified version of the HLATTICE code. From the output of the numerical simulation, we compute the probability distribution of curvature fluctuations, paying particular attention to sub-horizon scales. We find that in some specific models these modes grow to large amplitudes developing highly non-Gaussian probability distributions. We then calculate PBH abundances using the standard Press-Schechter criterion and find that overproduction of PBHs is likely in some regions of the chaotic preheating parameter space.

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Massive charged scalar field in the Kerr-Newman background II: Hawking   radiation

Published Paper #: 416

Authors:, R. A. Konoplya, A. Zhidenko,

Journal: Phys. Rev. D 89, 084015 (2014)

url: http://arxiv.org/pdf/1402.1998v3.pdf

Abstract: We perform accurate calculations of the energy-, momentum-, and charge-emission rates of a charged scalar field in the background of the Kerr-Newman black hole at the range of parameters for which the effect is not negligibly small and, at the same time, the semiclassical regime is, at least marginally, valid. For black holes with charge below or not much higher than the charge accretion limit $Q \sim \mu M/e$ (where $e$ and $\mu$ are the electron's mass and charge), the time between the consequent emitting of two charged particles is very large. For primordial black holes the transition between the increasing and decreasing of the ratio $Q/M$ occurs around the charge accretion limit. The rotation increases the intensity of radiation up to three orders, while the effect of the field's mass strongly suppresses the radiation.

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The Premature Formation of High Redshift Galaxies

Published Paper #: 415

Authors:, Fulvio Melia,

Journal: AJ 147, Issue 5, article id. 120, 7 pp. (2014)

url: http://arxiv.org/pdf/1403.0908v1.pdf

Abstract: Observations with WFC3/IR on the Hubble Space Telescope and the use of gravitational lensing techniques have facilitated the discovery of galaxies as far back as z ~ 10-12, a truly remarkable achievement. However, this rapid emergence of high-z galaxies, barely ~ 200 Myr after the transition from Population III star formation to Population II, appears to be in conflict with the standard view of how the early Universe evolved. This problem has much in common with the better known (and probably related) premature appearance of supermassive black holes at z ~ 6. It is difficult to understand how ~ 10^9 solar-mass black holes could have appeared so quickly after the big bang without invoking non-standard accretion physics and the formation of massive seeds, neither of which is seen in the local Universe. In earlier work, we showed that the appearance of high-z quasars could instead be understood more reasonably in the context of the R_h=ct Universe, which does not suffer from the same time compression issues as LCDM does at early epochs. Here, we build on that work by demonstrating that the evolutionary growth of primordial galaxies was consistent with the current view of how the first stars formed, but only with the timeline afforded by the R_h=ct cosmology. We also show that the growth of high-z quasars was mutually consistent with that of the earliest galaxies, though it is not yet clear whether the former grew from 5-20 solar-mass seeds created in Population III or Population II supernova explosions.

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One Hundred First Stars : Protostellar Evolution and the Final Masses

Published Paper #: 414

Authors:, Shingo Hirano, Takashi Hosokawa, Naoki Yoshida, Hideyuki Umeda, Kazuyuki Omukai, Gen Chiaki, Harold W. Yorke,

Journal: Astrophys.J.781:60-81,2014

url: http://arxiv.org/pdf/1308.4456v2.pdf

Abstract: We perform a large set of radiation hydrodynamics simulations of primordial star formation in a fully cosmological context. Our statistical sample of 100 First Stars show that the first generation of stars have a wide mass distribution M_popIII = 10 ~ 1000 M_sun. We first run cosmological simulations to generate a set of primordial star-forming gas clouds. We then follow protostar formation in each gas cloud and the subsequent protostellar evolution until the gas mass accretion onto the protostar is halted by stellar radiative feedback. The accretion rates differ significantly among the primordial gas clouds which largely determine the final stellar masses. For low accretion rates the growth of a protostar is self-regulated by radiative feedback effects and the final mass is limited to several tens of solar masses. At high accretion rates the protostar's outer envelope continues to expand and the effective surface temperature remains low; such protostars do not exert strong radiative feedback and can grow in excess to one hundred solar masses. The obtained wide mass range suggests that the first stars play a variety of roles in the early universe, by triggering both core-collapse supernovae and pair-instability supernovae as well as by leaving stellar mass black holes. We find certain correlations between the final stellar mass and the physical properties of the star-forming cloud. These correlations can be used to estimate the mass of the first star from the properties of the parent cloud or of the host halo, without following the detailed protostellar evolution.

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Primordial Black Holes as Heat Sources for Living Systems with Longest   Possible Lifetimes

Published Paper #: 413

Authors:, C Sivaram, Kenath Arun, Kiren O V,

Journal: Astrophysics and Space Science June 2014, Volume 351, Issue 2, pp
 407-408

url: http://arxiv.org/pdf/1412.4015v1.pdf

Abstract: Just forty years ago, Hawking wrote his famous paper on primordial black holes (PBH). There have been since innumerable discussions on the consequences of the existence of such exotic objects and ramifications of their properties. Here we suggest that PBH's in an ever expanding universe (as implied by dark energy domination, especially of a cosmological constant) could be the ultimate repository for long lived living systems. PBH's having solar surface temperatures would last 10^32 years as a steady power source and should be considered in any discussion on exobiological life.

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Identifying the most crucial parameters of the initial curvature profile   for primordial black hole formation

Published Paper #: 412

Authors:, Tomohiro Nakama, Tomohiro Harada, A. G. Polnarev, Jun'ichi Yokoyama,

Journal: JCAP01(2014)037

url: http://arxiv.org/pdf/1310.3007v2.pdf

Abstract: Primordial black holes (PBHs) are an important tool in cosmology to probe the primordial spectrum of small-scale curvature perturbations that reenter the cosmological horizon during radiation domination epoch. We numerically solve the evolution of spherically symmetric highly perturbed configurations to clarify the criteria of PBHs formation using an extremely wide class of curvature profiles characterized by five parameters, (in contrast to only two parameters used in all previous papers) which specify the curvature profiles not only at the central region but also at the outer boundary of configurations. It is shown that formation or non-formation of PBHs is determined entirely by only two master parameters one of which can be presented as an integral of curvature over initial configurations and the other is presented in terms of the position of the boundary and the edge of the core.

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Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH

Published Paper #: 411

Authors:, Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki, Ryo Matsuda,

Journal: Phys. Rev. D 89, 103501 (2014)

url: http://arxiv.org/pdf/1401.1909v2.pdf

Abstract: We investigate the consistency of a scenario in which the baryon asymmetry, dark matters, as well as the cosmic density perturbation are generated simultaneously through the evaporation of primordial black holes (PBHs). This scenario can explain the coincidence of the dark matter and the baryon density of the universe, and is free from the isocurvature perturbation problem. We show that this scenario predicts the masses of PBHs, right-handed neutrinos and dark matters, the Hubble scale during inflation, the non-gaussianity and the running of the spectral index. We also discuss the testability of the scenario by detecting high frequency gravitational waves from PBHs.

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Threshold of primordial black hole formation

Published Paper #: 410

Authors:, Tomohiro Harada, Chul-Moon Yoo, Kazunori Kohri,

Journal: Phys.Rev.D88:084051,2013

url: http://arxiv.org/pdf/1309.4201v4.pdf

Abstract: Based on a physical argument, we derive a new analytic formula for the amplitude of density perturbation at the threshold of primordial black hole formation in the universe dominated by a perfect fluid with the equation of state $p=w\rho c^{2}$ for $w\ge 0$. The formula gives $\delta^{\rm UH}_{H c}=\sin^{2}[\pi \sqrt{w}/(1+3w)]$ and $\tilde{\delta}_{c}=[3(1+w)/(5+3w)]\sin^{2}[\pi\sqrt{w}/(1+3w)]$, where $\delta^{\rm UH}_{H c}$ and $\tilde{\delta}_{c}$ are the amplitude of the density perturbation at the horizon crossing time in the uniform Hubble slice and the amplitude measure used in numerical simulations, respectively, while the conventional one gives $\delta^{\rm UH}_{H c}=w$ and $\tilde{\delta}_{c}=3w(1+w)/(5+3w)$. Our formula shows a much better agreement with the result of recent numerical simulations both qualitatively and quantitatively than the conventional formula. For a radiation fluid, our formula gives $\delta^{\rm UH}_{H c}=\sin^{2}(\sqrt{3}\pi/6)\simeq 0.6203$ and $\tilde{\delta}_{c}=(2/3)\sin^{2}(\sqrt{3}\pi/6)\simeq 0.4135$. We also discuss the maximum amplitude and the cosmological implications of the present result.

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Large Scale Cosmic Perturbation from Evaporation of Primordial Black   Holes

Published Paper #: 409

Authors:, Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki,

Journal: Phys. Rev. D 88, 123519 (2013)

url: http://arxiv.org/pdf/1306.6437v2.pdf

Abstract: We present a novel mechanism to generate the cosmic perturbation from evaporation of primordial black holes. A mass of a field is fluctuated if it is given by a vacuum expectation value of a light scalar field because of the quantum fluctuation during inflation. The fluctuated mass causes variations of the evaporation time of the primordial black holes. Therefore provided the primordial black holes dominate the universe when they evaporate, primordial cosmic perturbations are generated. We find that the amplitude of the large scale curvature perturbation generated in this scenario can be consistent with the observed value. Interestingly, our mechanism works even if all fields which are responsible for inflation and the generation of the cosmic perturbation are decoupled from the visible sector except for the gravitational interaction. An implication to the running spectral index is also discussed.

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PBH mass growth through radial accretion during the radiation dominated   era

Published Paper #: 408

Authors:, F. D. Lora-Clavijo, F. S. Guzman, A. Cruz-Osorio,

Journal: JCAP 12 (2013) 015

url: http://arxiv.org/pdf/1312.0989v1.pdf

Abstract: We model the radial accretion of radiation on Primordial Black Holes (PBH) by numerically solving Einstein's equations coupled to an ultrarelativistic ideal gas with equation of state $p=\rho/3$. We calculate the final mass of a black hole by the integration of the accreted radiation energy density during the leptonic era between $t\sim10^{-4}s$ to $t\sim 10^2s$ after the Big Bang. Our results indicate that small PBHs with initial masses between $10^{-4}$ to $1M_{\odot}$ may grow up to hundreds of solar masses, and thus can be SMBH seeds. On the other hand, PBHs formed at $t\sim 1s$ with initial mass between 900 and $\sim 980M_{\odot}$, by the time $t\sim 100s$ show masses of $10^4$ to $10^6M_{\odot}$ which are masses of seeds or already formed SMBHs. The fact that we consider only radial flow implies that our results work well as limiting cases, and it is expected that under more general scenarios the accretion rates may change significantly. Nevertheless we show that it is possible that SMBHs can be PBHs that grew due to the accretion of radiation.

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Formation and internal structure of superdense dark matter clumps and   ultracompact minihaloes

Published Paper #: 407

Authors:, V. S. Berezinsky, V. I. Dokuchaev, Yu. N. Eroshenko,

Journal: JCAP 11, 059 (2013)

url: http://arxiv.org/pdf/1308.6742v2.pdf

Abstract: We discuss the formation mechanisms and structure of the superdense dark matter clumps (SDMC) and ultracompact minihaloes (UCMH), outlining the differences between these types of DM objects. We define as SDMC the gravitationally bounded DM objects which have come into virial equilibrium at the radiation-dominated (RD) stage of the universe evolution. Such objects can be formed from the isocurvature (entropy) density perturbations or from the peaks in the spectrum of curvature (adiabatic) perturbation. The axion miniclusters (Kolb and Tkachev 1994) are the example of the former model. The system of central compact mass (e. g. in the form of SDMC or primordial black hole (PBH)) with the outer DM envelope formed in the process of secondary accretion we refer to as UCMH. Therefore, the SDMC can serve as the seed for the UCMH in some scenarios. Recently, the SDMC and UCMH were considered in the many works, and we try to systematize them here. We consider also the effect of asphericity of the initial density perturbation in the gravitational evolution, which decreases the SDMC amount and, as the result, suppresses the gamma-ray signal from DM annihilation.

Keywords: ::

Number Counts and Non-Gaussianity

Published Paper #: 406

Authors:, Sarah Shandera, Adrienne L. Erickcek, Pat Scott, Jhon Yana Galarza,

Journal: Phys. Rev. D 88, 103506 (2013)

url: http://arxiv.org/pdf/1211.7361v2.pdf

Abstract: We describe a general procedure for using number counts of any object to constrain the probability distribution of the primordial fluctuations, allowing for generic weak non-Gaussianity. We apply this procedure to use limits on the abundance of primordial black holes and dark matter ultracompact minihalos (UCMHs) to characterize the allowed statistics of primordial fluctuations on very small scales. We present constraints on the power spectrum and the amplitude of the skewness for two different families of non-Gaussian distributions, distinguished by the relative importance of higher moments. Although primordial black holes probe the smallest scales, ultracompact minihalos provide significantly stronger constraints on the power spectrum and so are more likely to eventually provide small-scale constraints on non-Gaussianity.

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Fundamental Particle Structure in the Cosmological Dark Matter

Published Paper #: 405

Authors:, Maxim Yu. Khlopov,

Journal: International Journal of Modern Physics A, Vol. 28 (2013) 1330042
 (60 pages)

url: http://arxiv.org/pdf/1311.2468v1.pdf

Abstract: The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro world and mechanisms of its symmetry breaking. Particle candidates for cosmological dark matter are lightest particles that bear new conserved quantum numbers. Dark matter particles may represent ideal gas of non-interacting particles. Self-interacting dark matter weakly or superweakly coupled to ordinary matter is also possible, reflecting nontrivial pattern of particle symmetry in the hidden sector of particle theory. In the early Universe the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which macroscopic cosmological defects or primordial nonlinear structures can be originated. Primordial black holes (PBHs) can be not only a candidate for dark matter, but also represent a universal probe for super-high energy physics in the early Universe. Evaporating PBHs turn to be a source of even superweakly interacting particles, while clouds of massive PBHs can serve as a nonlinear seeds for galaxy formation. The observed broken symmetry of the three known families may provide a simultaneous solution for the problems of the mass of neutrino and strong CP violation in the unique framework of models of horizontal unification. The existence of new stable charged leptons and quarks is possible, hidden in elusive "dark atoms". Such possibility, strongly restricted by the constraints on anomalous isotopes of light elements, is not excluded in scenarios that predict stable double charged particles. The excessive -2 charged particles are bound in these scenarios with primordial helium in O-helium "atoms", maintaining specific nuclear-interacting form of the dark matter, which may provide an interesting solution for the puzzles of the direct dark matter searches. (abridged)

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The instabilities and (anti)-evaporation of Schwarzschild-de Sitter   black holes in modified gravity

Published Paper #: 404

Authors:, L. Sebastiani, D. Momeni, R. Myrzakulov, S. D. Odintsov,

Journal: Physical Review D, V.88, N10, 104022 (2013) [17 pages]

url: http://arxiv.org/pdf/1305.4231v2.pdf

Abstract: We investigate the future evolution of Nariai black hole which is extremal limit of Schwarzschild-de Sitter one in modified gravity. The perturbations equations around Nariai black hole are derived in static and cosmological patches for general $F(R)$-gravity. The analytical and numerical study of several realistic $F(R)$-models shows the occurence of rich variety of scenarios: instabilities, celebrated Hawking evaporation and anti-evaporation of black hole. The realization of specific scenario depends on the model under consideration. It is remarkable that the presence of such primordial black holes at current universe may indicate towards the modified gravity which supports the anti-evaporation as preferrable model. As some generalization we extend the study of Nariai black hole evolution to modified Gauss-Bonnet gravity. The corresponding perturbations equations turn out to be much more complicated than in the case of $F(R)$ gravity. For specific example of modified Gauss-Bonnet gravity we demonstrate that Nariai solution maybe stable.

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Primordial black holes in non-Gaussian regimes

Published Paper #: 403

Authors:, Sam Young, Christian T. Byrnes,

Journal: JCAP 1308 (2013) 052

url: http://arxiv.org/pdf/1307.4995v2.pdf

Abstract: Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution - which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f_{NL}, g_{NL}, etc) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f_{NL} or g_{NL}, etc) does not give accurate results.

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Stars and Black Holes from the very Early Universe

Published Paper #: 402

Authors:, A. D. Dolgov, S. I. Blinnikov,

Journal: Phys. Rev. D 89, 021301 (2014)

url: http://arxiv.org/pdf/1309.3395v1.pdf

Abstract: A mechanism of creation of stellar-like objects in the very early universe, from the QCD phase transition till BBN and somewhat later, is studied. It is argued that in the considered process primordial black holes with masses above a few solar masses up to super-heavy ones could be created. This may explain an early quasar creation with evolved chemistry in surrounding medium and the low mass cutoff of the observed black holes. It is also shown that dense primordial stars can be created at the considered epoch. Such stars could later become very early supernovae and in particular high redshift gamma-bursters. In a version of the model some of the created objects can consist of antimatter.

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Constraining Primordial Black-Hole Bombs through Spectral Distortions of   the Cosmic Microwave Background

Published Paper #: 401

Authors:, Paolo Pani, Abraham Loeb,

Journal: Phys. Rev. D 88, 041301(R) (2013)

url: http://arxiv.org/pdf/1307.5176v2.pdf

Abstract: We consider the imprint of superradiant instabilities of nonevaporating primordial black holes (PBHs) on the spectrum of the cosmic microwave background (CMB). In the radiation dominated era, PBHs are surrounded by a roughly homogeneous cosmic plasma which endows photons with an effective mass through the plasma frequency. In this setting, spinning PBHs are unstable to a spontaneous spindown through the well-known "black-hole bomb" mechanism. At linear level, the photon density is trapped by the effective photon mass and grows exponentially in time due to superradiance. As the plasma density declines due to cosmic expansion, the associated energy around PBHs is released and dissipated in the CMB. We evaluate the resulting spectral distortions of the CMB in the redshift range 10^3 < z < 2x10^6. Using the existing COBE/FIRAS bounds on CMB spectral distortions, we derive upper limits on the fraction of dark matter that can be associated with spinning PBHs in the mass range 10^{-8}*Msun < M < 0.2*Msin. For maximally-spinning PBHs, our limits are much tighter than those derived from microlensing or other methods. Future data from the proposed PIXIE mission could improve our limits by several orders of magnitude.

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Primordial black holes as a tool for constraining non-Gaussianity

Published Paper #: 400

Authors:, Christian T. Byrnes, Edmund J. Copeland, Anne M. Green,

Journal: Phys. Rev. D86 043512 (2012)

url: http://arxiv.org/pdf/1206.4188v3.pdf

Abstract: Primordial Black Holes (PBH's) can form in the early Universe from the collapse of large density fluctuations. Tight observational limits on their abundance constrain the amplitude of the primordial fluctuations on very small scales which can not otherwise be constrained, with PBH's only forming from the extremely rare large fluctuations. The number of PBH's formed is therefore sensitive to small changes in the shape of the tail of the fluctuation distribution, which itself depends on the amount of non-Gaussianity present. We study, for the first time, how quadratic and cubic local non-Gaussianity of arbitrary size (parameterised by f_nl and g_nl respectively) affects the PBH abundance and the resulting constraints on the amplitude of the fluctuations on very small scales. Intriguingly we find that even non-linearity parameters of order unity have a significant impact on the PBH abundance. The sign of the non-Gaussianity is particularly important, with the constraint on the allowed fluctuation amplitude tightening by an order of magnitude as f_nl changes from just -0.5 to 0.5. We find that if PBH's are observed in the future, then regardless of the amplitude of the fluctuations, non-negligible negative f_nl would be ruled out. Finally we show that g_nl can have an even larger effect on the number of PBH's formed than f_nl.

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Primordial black hole production during preheating in a chaotic   inflationary model

Published Paper #: 399

Authors:, E. Torres-Lomas, L. Arturo Urena-Lopez,

Journal: AIP Conf.Proc. 1548 (2012) 238-243

url: http://arxiv.org/pdf/1308.1268v1.pdf

Abstract: In this paper we review the production of primordial black holes (PBHs) during preheating after a chaotic inflationary model. All relevant equations of motion are solved numerically in a modified version of HLattice, and we then calculate the mass variance to determine structure formation during preheating. It is found that production of PBHs can be a generic result of the model, even though the results seem to be sensitive to the values of the smoothing scale. We consider a constraint for overproduction of PBHs that could uncover some stress between inflation-preheating models and observations.

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Cosmological constraints on the curvaton web parameters

Published Paper #: 398

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys. Rev. D 88, 023521 (2013)

url: http://arxiv.org/pdf/1212.6529v2.pdf

Abstract: We consider the mixed inflaton-curvaton scenario in which quantum fluctuations of the curvaton field during inflation lead to a relatively large curvature perturbation spectrum at small scales. We use the model of chaotic inflation with quadratic potential including supergravity corrections leading to a large positive tilt in the power spectrum of the curvaton field. The model is characterized by the strongly inhomogeneous curvaton field in the Universe and large non-Gaussianity of curvature perturbations at small scales. We obtained the constraints on the model parameters considering the process of primordial black hole (PBH) production in radiation era.

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Constraints on primordial black holes as dark matter candidates from   capture by neutron stars

Published Paper #: 397

Authors:, Fabio Capela, Maxim Pshirkov, Peter Tinyakov,

Journal: Phys. Rev. D 87, 123524 (2013)

url: http://arxiv.org/pdf/1301.4984v3.pdf

Abstract: We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred GeV/cm$^3$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim 10^{24} \text{g}$. At the DM density of $2\times 10^3$ GeV/cm$^3$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

Keywords: ::

Semiclassical geons as solitonic black hole remnants

Published Paper #: 396

Authors:, Francisco S. N. Lobo, Gonzalo J. Olmo, D. Rubiera-Garcia,

Journal: JCAP 07 (2013) 011

url: http://arxiv.org/pdf/1306.2504v1.pdf

Abstract: We find that the end state of black hole evaporation could be represented by non-singular and without event horizon stable solitonic remnants with masses of the order the Planck scale and up to 16 units of charge. Though these objects are locally indistinguishable from spherically symmetric, massive electric (or magnetic) charges, they turn out to be sourceless geons containing a wormhole generated by the electromagnetic field. Our results are obtained by interpreting semiclassical corrections to Einstein's theory in the first-order (Palatini) formalism, which yields second-order equations and avoids the instabilities of the usual (metric) formulation of quadratic gravity. We also discuss the potential relevance of these solutions for primordial black holes and the dark matter problem.

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The influence of magnetic fields, turbulence, and UV radiation on the   formation of supermassive black holes

Published Paper #: 395

Authors:, C. Van Borm, M. Spaans,

Journal: A&A 553, L9 (2013)

url: http://arxiv.org/pdf/1304.4057v2.pdf

Abstract: Context. The seeds of the supermassive black holes (SMBHs) with masses of ~10^9 M_Sun observed already at z ~ 6 may have formed through the direct collapse of primordial gas in T_vir >~ 10^4 K halos, whereby the gas must stay hot (~10^4 K) in order to avoid fragmentation.   Aims. The interplay between magnetic fields, turbulence, and a UV radiation background during the gravitational collapse of primordial gas in a halo is explored; in particular, the possibilities for avoiding fragmentation are examined.   Methods. Using an analytical one-zone model, the evolution of a cloud of primordial gas is followed from its initial cosmic expansion through turnaround, virialization, and collapse up to a density of 10^7 cm-3.   Results. It was found that in halos with no significant turbulence, the critical UV background intensity (J_21^crit) for keeping the gas hot is lower by a factor ~10 for an initial comoving magnetic field B_0 ~ 2 nG than for the zero-field case, and even lower for stronger fields. In turbulent halos, J_21^crit is found to be a factor ~10 lower than for the zero-field-zero-turbulence case, and the stronger the turbulence (more massive halo and/or stronger turbulent heating) the lower J_21^crit.   Conclusions. The reduction in J_21^crit is particularly important, since it exponentially increases the number of halos exposed to a supercritical radiation background.

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Resonant high energy graviton to photon conversion at post recombination   epoch

Published Paper #: 394

Authors:, Alexander D. Dolgov, Damian Ejlli,

Journal: Phys. Rev. D 87, 104007 (2013)

url: http://arxiv.org/pdf/1303.1556v2.pdf

Abstract: Resonant conversion of high energy gravitons into photons in large scale cosmological magnetic fields at the post recombination epoch is considered. It is shown that the probability of the resonance photon production is much higher than the non-resonant one. As a result an observable isotropic background of cosmic gamma rays might be created. As shown in our previous paper, an early population of primordial black holes (PBHs) prior to big bang nucleosynthesis (BBN) could be an efficient source of high frequency gravitational waves. For the primordial black hole mass about $10^8$ g the produced photons would be the dominant component of the soft to hard Cosmic X-ray Background (CXB) and for lower masses the spectrum is shifted down to the ultraviolet and optic.

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Evolution of Primordial Black Hole Mass Spectrum in Brans-Dicke Theory

Published Paper #: 393

Authors:, Debabrata Dwivedee, Bibekananda Nayak, Lambodar Prasad Singh,

Journal: Int. J. Mod. Phys. D 22, 1350022 (2013)

url: http://arxiv.org/pdf/1208.5115v2.pdf

Abstract: We investigate the evolution of primordial black hole mass spectrum by including both accretion of radiation and Hawking evaporation within Brans-Dicke cosmology in radiation, matter and vacuum-dominated eras. We also consider the effect of evaporation of primordial black holes on the expansion dynamics of the universe. The analytic solutions describing the energy density of the black holes in equilibrium with radiation are presented. We demonstrate that these solutions act as attractors for the system ensuring stability for both linear and nonlinear situations. We show, however, that inclusion of accretion of radiation delays the onset of this equilibrium in all radiation, matter and vacuum-dominated eras.

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Primordial black hole formation in the early universe: critical   behaviour and self-similarity

Published Paper #: 392

Authors:, Ilia Musco, John C. Miller,

Journal: Class. Quantum Grav. 30 145009 (2013)

url: http://arxiv.org/pdf/1201.2379v3.pdf

Abstract: Following on after three previous papers discussing the formation of primordial black holes during the radiative era of the early universe, we present here a further investigation of the critical nature of the process involved, aimed at making contact with some of the basic underlying ideas from the literature on critical collapse. We focus on the intermediate state, which we have found appearing in cases with perturbations close to the critical limit, and examine the connection between this and the similarity solutions which play a fundamental role in the standard picture of critical collapse. We have derived a set of self-similar equations for the null-slicing form of the metric which we are using for our numerical calculations, and have then compared the results obtained by integrating these with the ones coming from our simulations for collapse of cosmological perturbations within an expanding universe. We find that the similarity solution is asymptotically approached in a region which grows to cover both the contracting matter and part of the semi-void which forms outside it. Our main interest is in the situation relevant for primordial black hole formation in the radiative era of the early universe, where the relation between the pressure $p$ and the energy density $e$ can be reasonably approximated by an expression of the form $p = we$ with $w=1/3$. However, we have also looked at other values of $w$, both because these have been considered in previous literature and also because they can be helpful for giving further insight into situations relevant for primordial black hole formation. As in our previous work, we have started our simulations with initial supra-horizon scale perturbations of a type which could have come from inflation.

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Primordial black hole formation from an axion-like curvaton model

Published Paper #: 391

Authors:, Masahiro Kawasaki, Naoya Kitajima, Tsutomu T. Yanagida,

Journal: Phys.Rev.D87:063519,2013

url: http://arxiv.org/pdf/1207.2550v2.pdf

Abstract: We argue that the existence of the cold dark matter is explained by primordial black holes.We show that a significant number of primordial black holes can be formed in an axion-like curvaton model, in which the highly blue-tilted power spectrum of primordial curvature perturbations is achieved.It is found that the produced black holes with masses $\sim 10^{20} -10^{38} \mathrm{g}$ account for the present cold dark matter.We also argue the possibility of forming the primordial black holes with mass $\sim 10^5 M_{\odot}$ as seeds of the supermassive black holes.

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Primordial black hole constraints for curvaton models with predicted   large non-Gaussianity

Published Paper #: 390

Authors:, E. V. Bugaev, P. A. Klimai,

Journal: Int. J. Mod. Phys. D 22, 1350034 (2013)

url: http://arxiv.org/pdf/1303.3146v1.pdf

Abstract: We consider the early Universe scenario which allows for production of non-Gaussian curvature perturbations at small scales. We study the peculiarities of a formation of primordial black holes (PBHs) connected with the non-Gaussianity. In particular, we show that PBH constraints on the values of curvature perturbation power spectrum amplitude are strongly dependent on the shape of perturbations and can significantly (by two orders of magnitude) deviate from the usual Gaussian limit ${\cal P}_\zeta \lesssim 10^{-2}$. We give examples of PBH mass spectra calculations and PBH constraints for the particular case of the curvaton model.

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On the gravitational wave background from compact binary coalescences in   the band of ground-based interferometers

Published Paper #: 389

Authors:, Xing-Jiang Zhu, Eric J. Howell, David G. Blair, Zong-Hong Zhu,

Journal: MNRAS (2013) 431: 882-899

url: http://arxiv.org/pdf/1209.0595v4.pdf

Abstract: This paper reports a comprehensive study on the gravitational wave (GW) background from compact binary coalescences. We consider in our calculations newly available observation-based neutron star and black hole mass distributions and complete analytical waveforms that include post-Newtonian amplitude corrections. Our results show that: (i) post-Newtonian effects cause a small reduction in the GW background signal; (ii) below 100 Hz the background depends primarily on the local coalescence rate $r_0$ and the average chirp mass and is independent of the chirp mass distribution; (iii) the effects of cosmic star formation rates and delay times between the formation and merger of binaries are linear below 100 Hz and can be represented by a single parameter within a factor of ~ 2; (iv) a simple power law model of the energy density parameter $\Omega_{GW}(f) ~ f^{2/3}$ up to 50-100 Hz is sufficient to be used as a search template for ground-based interferometers. In terms of the detection prospects of the background signal, we show that: (i) detection (a signal-to-noise ratio of 3) within one year of observation by the Advanced LIGO detectors (H1-L1) requires a coalescence rate of $r_0 = 3 (0.2) Mpc^{-3} Myr^{-1}$ for binary neutron stars (binary black holes); (ii) this limit on $r_0$ could be reduced 3-fold for two co-located detectors, whereas the currently proposed worldwide network of advanced instruments gives only ~ 30% improvement in detectability; (iii) the improved sensitivity of the planned Einstein Telescope allows not only confident detection of the background but also the high frequency components of the spectrum to be measured. Finally we show that sub-threshold binary neutron star merger events produce a strong foreground, which could be an issue for future terrestrial stochastic searches of primordial GWs.

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Improved constraints on the primordial power spectrum at small scales   from ultracompact minihalos

Published Paper #: 388

Authors:, Torsten Bringmann, Pat Scott, Yashar Akrami,

Journal: Phys. Rev. D 85, 125027 (2012)

url: http://arxiv.org/pdf/1110.2484v3.pdf

Abstract: For a Gaussian spectrum of primordial density fluctuations, ultracompact minihalos (UCMHs) of dark matter are expected to be produced in much greater abundance than, e.g., primordial black holes. Forming shortly after matter-radiation equality, these objects would develop very dense and spiky dark matter profiles. In the standard scenario where dark matter consists of thermally-produced, weakly-interacting massive particles, UCMHs could thus appear as highly luminous gamma-ray sources, or leave an imprint in the cosmic microwave background by changing the reionisation history of the Universe. We derive corresponding limits on the cosmic abundance of UCMHs at different epochs, and translate them into constraints on the primordial power spectrum. We find the resulting constraints to be quite severe, especially at length scales much smaller than what can be directly probed by the cosmic microwave background or large-scale structure observations. We use our results to provide an updated compilation of the best available constraints on the power of density fluctuations on all scales, ranging from the present-day horizon to scales more than 20 orders of magnitude smaller.

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AGN III - primordial activity in nuclei of late-type galaxies with   pseudobulges

Published Paper #: 387

Authors:, B. V. Komberg, A. A. Ermash,

Journal: Astronomy Reports, vol.57, issue 6, pages 401-409, 2013

url: http://arxiv.org/pdf/1302.2942v1.pdf

Abstract: 1. Based on observational data on evolution of quasars and galaxies of different types along with the results of numerical simulations we make a conclusion that on low redshifts ($z<0.5$) QSOI/II objects in massive elliptical and spiral galaxies with classical bulges cannot be in late single activity event (be "primordial"). Instead of it they have had events of activity earlier in their evolution. It means that their presence on low redshifts is connected with the recurrence phenomenon, sequential wet minor mergings, because timescale of the activity does not exceed several units of $10^7$ years.   2. We define a new class - "AGN III" as active galactic nuclei in isolated late-type spirals with low-mass rapidly rotating pseudobulges. We also state that only such objects can be in the primordial phase of activity at low redshifts. Black holes in such galaxies have masses $M_{BH}<10^7M_\odot$ and also, probably very high spin. Such properties can explain their peculiar emission spectra.   A good representative of AGN III might be the galaxies with narrow (${\rm FWHM}(H\beta)\leq1200$ km/s) broad permitted emission lines - NLS. It is believed that their black hole masses are less than $M_{BH}<10^7M_\odot$ and their host galaxies have pseudobulges instead of the classical ones. Because host galaxies of NLS have pseudobulges and BLS (Broad-Line Seyfert galaxies) have classical bulges these two types of objects cannot have evolutionary connection. Presumably, the parent population of NLS are the quasars of "population A".

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Constraints on primordial black holes as dark matter candidates from   star formation

Published Paper #: 386

Authors:, Fabio Capela, Maxim Pshirkov, Peter Tinyakov,

Journal: Phys. Rev. D 87, 023507 (2013)

url: http://arxiv.org/pdf/1209.6021v3.pdf

Abstract: By considering adiabatic contraction of the dark matter (DM) during star formation, we estimate the amount of DM trapped in stars at their birth. If the DM consists partly of primordial black holes (PBHs), they will be trapped together with the rest of the DM and will be finally inherited by a star compact remnant --- a white dwarf (WD) or a neutron star (NS), which they will destroy in a short time. Observations of WDs and NSs thus impose constraints on the abundance of PBH. We show that the best constraints come from WDs and NSs in globular clusters which exclude the DM consisting entirely of PBH in the mass range $10^{16}{\rm g} - 3\times 10^{22}{\rm g}$, with the strongest constraint on the fraction $\Omega_{\rm PBH} /\Omega_{\rm DM}\lesssim 10^{-2}$ being in the range of PBH masses $10^{17}{\rm g} - 10^{18}$ g.

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Spacetimes with Singularities

Published Paper #: 385

Authors:, Ovidiu Cristinel Stoica,

Journal: An. St. Univ. Ovidius Constanta (2012) vol. 20(2), 213-238

url: http://arxiv.org/pdf/1108.5099v4.pdf

Abstract: We report on some advances made in the problem of singularities in general relativity.   First is introduced the singular semi-Riemannian geometry for metrics which can change their signature (in particular be degenerate). The standard operations like covariant contraction, covariant derivative, and constructions like the Riemann curvature are usually prohibited by the fact that the metric is not invertible. The things become even worse at the points where the signature changes. We show that we can still do many of these operations, in a different framework which we propose. This allows the writing of an equivalent form of Einstein's equation, which works for degenerate metric too.   Once we make the singularities manageable from mathematical viewpoint, we can extend analytically the black hole solutions and then choose from the maximal extensions globally hyperbolic regions. Then we find space-like foliations for these regions, with the implication that the initial data can be preserved in reasonable situations. We propose qualitative models of non-primordial and/or evaporating black holes.   We supplement the material with a brief note reporting on progress made since this talk was given, which shows that we can analytically extend the Schwarzschild and Reissner-Nordstrom metrics at and beyond the singularities, and the singularities can be made degenerate and handled with the mathematical apparatus we developed.

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ASTROD-GW: Overview and Progress

Published Paper #: 384

Authors:, Wei-Tou Ni,

Journal: International Journal of Modern Physics D Vol. 22, No. 1 (2013)
 1341004 (33 pages)

url: http://arxiv.org/pdf/1212.2816v2.pdf

Abstract: In this paper, we present an overview of ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitational Wave [GW] detection) mission concept and its studies. ASTROD-GW is an optimization of ASTROD which focuses on low frequency gravitational wave detection. The detection sensitivity is shifted by a factor of 260 (52) towards longer wavelengths compared with that of NGO/eLISA (LISA). The mission consists of three spacecraft, each of which orbits near one of the Sun-Earth Lagrange points (L3, L4 and L5), such that the array forms an almost equilateral triangle. The 3 spacecraft range interferometrically with one another with an arm length of about 260 million kilometers. The orbits have been optimized resulting in arm length changes of less than 0.00015 AU or, fractionally, less than 10^(-4) in twenty years, and relative Doppler velocities of the three spacecraft of less than 3 m/s. In this paper, we present an overview of the mission covering: the scientific aims, the sensitivity spectrum, the basic orbit configuration, the simulation and optimization of the spacecraft orbits, the deployment of ASTROD-GW formation, TDI (Time Delay Interferometry) and the payload. The science goals are the detection of GWs from (i) Supermassive Black Holes; (ii) Extreme-Mass-Ratio Black Hole Inspirals; (iii) Intermediate-Mass Black Holes; (iv) Galactic Compact Binaries and (v) Relic Gravitational Wave Background. For the purposes of primordial GW detection, a six spacecraft formation would be needed to enable the correlated detection of stochastic GWs. A brief discussion of the six spacecraft orbit optimization is also presented.

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Conversion of relic gravitational waves into photons in cosmological   magnetic fields

Published Paper #: 383

Authors:, Alexander D. Dolgov, Damian Ejlli,

Journal: JCAP 1212 (2012) 003

url: http://arxiv.org/pdf/1211.0500v2.pdf

Abstract: Conversion of gravitational waves into electromagnetic radiation is discussed. The probability of transformations of gravitons into photons in presence of cosmological background magnetic field is calculated at the recombination epoch and during subsequent cosmological stages. The produced electromagnetic radiation is concentrated in the X-ray part of the spectrum. It is shown that if the early Universe was dominated by primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN), the relic gravitons emitted by PBHs would transform to an almost isotropic background of electromagnetic radiation due to conversion of gravitons into photons in cosmological magnetic fields. Such extragalactic radiation could be noticeable or even dominant component of Cosmic X-ray Background.

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Primordial black hole formation from non-Gaussian curvature   perturbations

Published Paper #: 382

Authors:, P. A. Klimai, E. V. Bugaev,

Journal: Proc. of 17th Int. Seminar QUARKS-2012, Yaroslavl, Russia, June
 4-10, 2012; Vol. 2, pp. 163-174; Moscow, 2013

url: http://arxiv.org/pdf/1210.3262v2.pdf

Abstract: We consider several early Universe models that allow for production of large curvature perturbations at small scales. As is well known, such perturbations can lead to formation of primordial black holes (PBHs). We briefly review the today's situation with PBH constraints and then focus on two models in which strongly non-Gaussian curvature perturbations are predicted: the hybrid inflation waterfall model and the curvaton model. We show that PBH constraints on the values of curvature perturbation power spectrum amplitude are strongly dependent on the shape of perturbations and can significantly (by two orders of magnitude) deviate from the usual Gaussian limit ${\cal P}_\zeta \lesssim 10^{-2}$. We give examples of PBH mass spectra calculations for both inflationary models.

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Clusters of Black Holes as Point-Like Gamma-ray Sources

Published Paper #: 381

Authors:, K. M. Belotsky, A. V. Berkov, A. A. Kirillov, S. G. Rubin,

Journal: Astroparticle Physics 35 (2011) 28-32

url: http://arxiv.org/pdf/1212.2524v1.pdf

Abstract: The possibility of identifying some of Galactic gamma-ray sources as clusters of primordial black holes is discussed. The known scenarios of supermassive black hole formation indicate the multiple formation of lower-mass black holes. Our analysis demonstrates that due to Hawking evaporation the cluster of black holes with masses about $10^{15}$ g could be observed as a gamma-ray source. The total mass of typical cluster is $\sim 10 M_\odot$. Detailed calculations have been performed on the basis of specific model of primordial black hole formation.

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Self-consistent initial conditions for primordial black hole formation

Published Paper #: 380

Authors:, A. G. Polnarev, Tomohiro Nakama, Jun'ichi Yokoyama,

Journal: JCAP09(2012)027

url: http://arxiv.org/pdf/1204.6601v2.pdf

Abstract: For an arbitrary strong, spherically symmetric super-horizon curvature perturbation, we present analytical solutions of the Einstein equations in terms of asymptotic expansion over the ratio of the Hubble radius to the length-scale of the curvature perturbation under consideration. To obtain this solution we develop a recursive method of quasi-linearization which reduces the problem to a system of coupled ordinary differential equations for the $N$-th order terms in the asymptotic expansion with sources consisting of a non-linear combination of the lower order terms. We use this solution for setting initial conditions for subsequent numerical computations. For an arbitrary precision requirement predetermined by the intended accuracy and stability of the computer code, our analytical solution yields optimal truncated asymptotic expansion which can be used to find the upper limit on the moment of time when the initial conditions expressed in terms of such truncated expansion should be set. Examples of how these truncated (up to eighth order) solutions provide initial conditions with given accuracy for different radial profiles of curvature perturbations are presented.

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Observable Spectra of Induced Gravitational Waves from Inflation

Published Paper #: 379

Authors:, Laila Alabidi, Kazunori Kohri, Misao Sasaki, Yuuiti Sendouda,

Journal: JCAP 09:017, 2012

url: http://arxiv.org/pdf/1203.4663v2.pdf

Abstract: Measuring the primordial power spectrum on small scales is a powerful tool in inflation model building, yet constraints from Cosmic Microwave Background measurements alone are insufficient to place bounds stringent enough to be appreciably effective. For the very small scale spectrum, those which subtend angles of less than 0.3 degrees on the sky, an upper bound can be extracted from the astrophysical constraints on the possible production of primordial black holes in the early universe. A recently discovered observational by-product of an enhanced power spectrum on small scales, induced gravitational waves, have been shown to be within the range of proposed space based gravitational wave detectors; such as NASA's LISA and BBO detectors, and the Japanese DECIGO detector. In this paper we explore the impact such a detection would have on models of inflation known to lead to an enhanced power spectrum on small scales, namely the Hilltop-type and running mass models. We find that the Hilltop-type model can produce observable induced gravitational waves within the range of BBO and DECIGO for integral and fractional powers of the potential within a reasonable number of e-folds. We also find that the running mass model can produce a spectrum within the range of these detectors, but require that inflation terminates after an unreasonably small number of e-folds. Finally, we argue that if the thermal history of the Universe were to accomodate such a small number of e-folds the Running Mass Model can produce Primordial Black Holes within a mass range compatible with Dark Matter, i.e. within a mass range 10^{20}g< M_{BH}<10^{27}g.

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Unimodular bimode gravity and the coherent scalar-graviton field as   galaxy dark matter

Published Paper #: 378

Authors:, Yu. F. Pirogov,

Journal: Eur. Phys. J. C 72 (2012) 2017

url: http://arxiv.org/pdf/1111.1437v3.pdf

Abstract: The explicit violation of the general gauge invariance/relativity is adopted as the origin of dark matter and dark energy of the gravitational nature. The violation of the local scale invariance alone, with the residual unimodular one, is considered. Besides the four-volume preserving deformation mode -- the transverse-tensor graviton -- the metric comprises a compression mode -- the scalar graviton, or the systolon. A unimodular invariant and general covariant metric theory of the bimode/scalar-tensor gravity is consistently worked out. To reduce the primordial ambiguity of the theory a dynamical global symmetry is imposed, with its subsequent spontaneous breaking revealed. The static spherically symmetric case in the empty, but possibly for the origin, space is studied. A three-parameter solution describing a new static space structure -- the dark lacuna -- is constructed. It enjoys the property of gravitational confinement, with the logarithmic potential of gravitational attraction at the periphery, and results in the asymptotically flat rotation curves. Comprising a super-massive dark fracture (a scalar-modified black hole) at the origin surrounded by a cored dark halo, the dark lacunas are proposed as a prototype model of galaxies, implying an ultimate account for the distributed non-gravitational matter and a putative asphericity or rotation.

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A new probe of the small-scale primordial power spectrum: astrometric   microlensing by ultracompact minihalos

Published Paper #: 377

Authors:, Fangda Li, Adrienne L. Erickcek, Nicholas M. Law,

Journal: Phys.Rev.D86,043519(2012)

url: http://arxiv.org/pdf/1202.1284v2.pdf

Abstract: The dark matter enclosed in a density perturbation with a large initial amplitude (delta-rho/rho > 1e-3) collapses shortly after recombination and forms an ultracompact minihalo (UCMH). Their high central densities make UCMHs especially suitable for detection via astrometric microlensing: as the UCMH moves, it changes the apparent position of background stars. A UCMH with a mass larger than a few solar masses can produce a distinctive astrometric microlensing signal that is detectable by the space astrometry mission Gaia. If Gaia does not detect gravitational lensing by any UCMHs, then it establishes an upper limit on their abundance and constrains the amplitude of the primordial power spectrum for k~2700 Mpc^{-1}. These constraints complement the upper bound on the amplitude of the primordial power spectrum derived from limits on gamma-ray emission from UCMHs because the astrometric microlensing signal produced by an UCMH is maximized if the dark-matter annihilation rate is too low to affect the UCMH's density profile. If dark matter annihilation within UCMHs is not detectable, a search for UCMHs by Gaia could constrain the amplitude of the primordial power spectrum to be less than 1e-5; this bound is three orders of magnitude stronger than the bound derived from the absence of primordial black holes.

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Primordial Black Hole Evaporation and Spontaneous Dimensional Reduction

Published Paper #: 376

Authors:, J. R. Mureika,

Journal: Phys. Lett. B 716, 171-175 (2012)

url: http://arxiv.org/pdf/1204.3619v3.pdf

Abstract: Several different approaches to quantum gravity suggest the effective dimension of spacetime reduces from four to two near the Planck scale. In light of such evidence, this letter re-examines the thermodynamics of primordial black holes (PBHs) in specific lower-dimensional gravitational models. Unlike in four dimensions, $\done$-D black holes radiate with power $P \sim \Mbh^2$, while it is known no $(2+1)-$D (BTZ) black holes can exist in a non-anti-deSitter universe. This has important relevance to the PBH population size and distribution, and consequently on cosmological evolution scenarios. The number of PBHs that have evaporated to present day is estimated, assuming they account for all dark matter. Entropy conservation during dimensional transition imposes additional constraints. If the cosmological constant is non-negative, no black holes can exist in the $(2+1)$-dimensional epoch, and consequently a $(1+1)$-dimensional black hole will evolve to become a new type of remnant. Although these results are conjectural and likely model-dependent, they open new questions about the viability of PBHs as dark matter candidates.

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Accretion of non-minimally coupled generalized Chaplygin gas into black   holes

Published Paper #: 375

Authors:, Manuela G. Rodrigues, Alex E. Bernardini,

Journal: Int. J. Mod. Phys. D21, 1250075 (2012)

url: http://arxiv.org/pdf/1208.1572v1.pdf

Abstract: The mass evolution of Schwarzschild black holes by the absorption of scalar fields is investigated in the scenario of the generalized Chaplygin gas (GCG). The GCG works as a unification picture of dark matter plus dark energy that naturally accelerates the expansion of the Universe. Through elements of the quasi-stationary approach, we consider the mass evolution of Schwarzschild black holes accreted by non-minimally coupled cosmological scalar fields reproducing the dynamics of the GCG. As a scalar field non-minimally coupled to the metrics, such an exotic content has been interconnected with accreting black holes. The black hole increasing masses by the absorption of the gas reflects some consistence of the accretion mechanism with the hypothesis of the primordial origin of supermassive black holes. Our results effectively show that the non-minimal coupling with the GCG dark sector accelerates the increasing of black hole masses. Meanwhile some exotic features can also be depicted for specific ranges of the non-minimal coupling in which the GCG dynamics is substantially modified.

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Schwarzschild black holes can wear scalar wigs

Published Paper #: 374

Authors:, Juan Barranco, Argelia Bernal, Juan Carlos Degollado, Alberto Diez-Tejedor, Miguel Megevand, Miguel Alcubierre, Darío Núñez, Olivier Sarbach,

Journal: Phys. Rev. Lett. 109, 081102 (2012)

url: http://arxiv.org/pdf/1207.2153v1.pdf

Abstract: We study the evolution of a massive scalar field surrounding a Schwarzschild black hole and find configurations that can survive for arbitrarily long times, provided the black hole or the scalar field mass is small enough. In particular, both ultra-light scalar field dark matter around supermassive black holes and axion-like scalar fields around primordial black holes can survive for cosmological times. Moreover, these results are quite generic, in the sense that fairly arbitrary initial data evolves, at late times, as a combination of those long-lived configurations.

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Detecting unresolved moving sources in a diffuse background

Published Paper #: 373

Authors:, Alex Geringer-Sameth, Savvas M. Koushiappas,

Journal: Monthly Notices of the Royal Astronomical Society, Vol. 425, pp.
 862-877 (2012)

url: http://arxiv.org/pdf/1012.1873v2.pdf

Abstract: We present a statistical technique which can be used to detect the presence and properties of moving sources contributing to a diffuse background. The method is a generalization of the 2-point correlation function to include temporal as well as spatial information. We develop a formalism which allows for a derivation of the spacetime 2-point function in terms of the properties of the contributing sources. We test this technique in simulated sky maps, and demonstrate its robustness in identifying the presence of moving and stationary sources. Applications of this formalism to the diffuse gamma-ray background include searches for solar system bodies, fast moving primordial black holes, and dense cores of dark matter proto-halos in the solar neighborhood. Other applications include detecting the contribution of energetic neutrinos originating in the solar system, as well as probing compact objects in long timeline lensing experiments.

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Constraints on small-scale cosmological perturbations from gamma-ray   searches for dark matter

Published Paper #: 372

Authors:, Pat Scott, Torsten Bringmann, Yashar Akrami,

Journal: J. Phys.: Conf. Ser. 375 (2012) 032012

url: http://arxiv.org/pdf/1205.1432v1.pdf

Abstract: Events like inflation or phase transitions can produce large density perturbations on very small scales in the early Universe. Probes of small scales are therefore useful for e.g. discriminating between inflationary models. Until recently, the only such constraint came from non-observation of primordial black holes (PBHs), associated with the largest perturbations. Moderate-amplitude perturbations can collapse shortly after matter-radiation equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent targets for indirect detection. Here we discuss the gamma-ray fluxes expected from UCMHs, the prospects of observing them with gamma-ray telescopes, and limits upon the primordial power spectrum derived from their non-observation by the Fermi Large Area Space Telescope.

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Formation of primordial black holes from non-Gaussian perturbations   produced in a waterfall transition

Published Paper #: 371

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys.Rev.D85:103504,2012

url: http://arxiv.org/pdf/1112.5601v2.pdf

Abstract: We consider the process of primordial black hole (PBH) formation originated from primordial curvature perturbations produced during waterfall transition (with tachyonic instability), at the end of hybrid inflation. It is known that in such inflation models, rather large values of curvature perturbation amplitudes can be reached, which can potentially cause a significant PBH production in the early Universe. The probability distributions of density perturbation amplitudes in this case can be strongly non-Gaussian, which requires a special treatment. We calculated PBH abundances and PBH mass spectra for the model, and analyzed their dependence on model parameters. We obtained the constraints on the parameters of the inflationary potential, using the available limits on $\beta_{PBH}$.

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Primordial seeds of supermassive black holes

Published Paper #: 370

Authors:, Masahiro Kawasaki, Alexander Kusenko, Tsutomu T. Yanagida,

Journal: Physics Letters B 711 (2012) 1

url: http://arxiv.org/pdf/1202.3848v2.pdf

Abstract: Supermassive black holes exist in the centers of galaxies, including Milky Way, but there is no compelling theory of their formation. Furthermore, observations of quasars imply that supermassive black holes have already existed at some very high redshifts, suggesting the possibility of their primordial origin. In a class of well-motivated models, inflationary epoch could include two or more periods of inflation dominated by different scalar fields. The transition between such periods of inflation could enhance the spectrum of density perturbations on some specific scale, which could lead to formation of primordial black holes with a very narrow range of masses of the order of 10^5 solar masses. These primordial black holes could have provided the requisite seeds for the observed population of supermassive black holes.

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Fourth level MSSM inflation from new flat directions

Published Paper #: 369

Authors:, Sayantan Choudhury, Supratik Pal,

Journal: JCAP 04 (2012) 018

url: http://arxiv.org/pdf/1111.3441v3.pdf

Abstract: We propose a model of inflation driven by minimal extension of SUSY, commonly known as MSSM. Starting from gauge invariant flat directions in the n = 4 level comprising of QQQL,QuQd,QuLe and uude, we construct the inflaton potential and employ it to investigate for its consequences around the saddle point arising from the non-vanishing fourth derivative of the original potential. To this end, we derive the expressions for the important parameters in MSSM inflation using the loop corrected potential. We further estimate the observable parameters and find them to fit well with recent observational data from WMAP7 by using the code CAMB. We also explore the possibility of primordial black hole formation from our model. Finally, we analyze one loop RGE and compute different phenomenological parameters which could be precisely determined in LHC or future Linear Colliders.

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Implications of a viscosity bound on black hole accretion

Published Paper #: 368

Authors:, Aninda Sinha, Banibrata Mukhopadhyay,

Journal: Phys. Lett. B709 (2012) 289-292

url: http://arxiv.org/pdf/1108.5177v2.pdf

Abstract: Motivated by the viscosity bound in gauge/gravity duality, we consider the ratio of shear viscosity (eta) to entropy density (s) in black hole accretion flows. We use both an ideal gas equation of state and the QCD equation of state obtained from lattice for the fluid accreting onto a Kerr black hole. The QCD equation of state is considered since the temperature of accreting matter is expected to approach 10^{12}K in certain hot flows. We find that in both the cases eta/s is small only for primordial black holes and several orders of magnitude larger than any known fluid for stellar and supermassive black holes. We show that a lower bound on the mass of primordial black holes leads to a lower bound on eta/s and vice versa. Finally we speculate that the Shakura-Sunyaev viscosity parameter should decrease with increasing density and/or temperatures.

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Evolution of Primordial Black Holes in Loop Quantum Gravity

Published Paper #: 367

Authors:, Debabrata Dwivedee, Bibekananda Nayak, Mubasher Jamil, Lambodar Prasad Singh,

Journal: J. Astrophys. Astr. (2014) 35, 97-106

url: http://arxiv.org/pdf/1110.6350v2.pdf

Abstract: In this work, we study the evolution of Primordial Black Holes within the context of Loop Quantum Gravity. First we calculate the scale factor and energy density of the universe for different cosmic era and then taking these as inputs we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum gravity even though a larger number of primordial black holes may form in early universe in comparison with Einstein's or scalar-tensor theories.

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Can the Reissner-Nordström black hole or Schwarzschild black hole be   the stable Planck-scale particle accelerator?

Published Paper #: 366

Authors:, Yi Zhu, Shao-Feng Wu, Yin Jiang, Guo-Hong Yang,

Journal: Phys. Rev. D 84, 123002 (2011)

url: http://arxiv.org/pdf/1108.1843v2.pdf

Abstract: It is shown that the extremal Reissner-Nordstr\"{o}m black hole, the non-extremal one with multiple scattering particles, and the Schwarzschild black hole with radial head-on particles are stable under the collision of the particles near the horizon, if the back-reaction effect and the effect generated by gravity of particles are involved. Moreover, the collision near Reissner-Nordstr\"{o}m black holes with astrophysically typical mass can not generate the Planck-scale center-of-mass energy. However, the head-on collision near the typical primordial black hole could just occur at the Planck-energy scale.

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Clustering of Primordial Black Holes. II. Evolution of Bound Systems

Published Paper #: 365

Authors:, James R. Chisholm,

Journal: Phys. Rev. D 84, 124031 (2011)

url: http://arxiv.org/pdf/1110.4402v1.pdf

Abstract: Primordial Black Holes (PBHs) that form from the collapse of density perturbations are more clustered than the underlying density field. In a previous paper, we showed the constraints that this has on the prospects of PBH dark matter. In this paper we examine another consequence of this clustering: the formation of bound systems of PBHs in the early universe. These would hypothetically be the earliest gravitationally collapsed structures, forming when the universe is still radiation dominated. Depending upon the size and occupation of the clusters, PBH merging occurs before they would have otherwise evaporated due to Hawking evaporation.

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Constraints on vector unparticle physics from cosmic censorship

Published Paper #: 364

Authors:, J. R. Mureika,

Journal: Int. J. Theor. Phys. 51, 1259-1267 (2012)

url: http://arxiv.org/pdf/0909.4511v2.pdf

Abstract: Vector unparticle couplings to standard model fields produce repulsive corrections to gravity. From a general relativistic perspective, this leads to an effective Reissner-Nordstr\"om-like metric whose "charge" is a function of the unparticle coupling constant $\lambda$, and therefore can admit naked singularities. Requiring the system to respect cosmic censorship provides a new method of constraining the value of $\lambda$. These limits are extremely loose for stellar-mass black holes, but commensurate with existing bounds for primordial black holes. In the case of theoretical low-mass black holes, the bounds on $\lambda$ are much stricter than those derived from astrophysical and accelerator phenomenology. Additional constraints on the lower limit of $\lambda$ are used to estimate the mass of the smallest possible black hole $\Mbh^{\rm min}$ that can be formed in the unparticle framework, as a function of the unparticle parameters ($\Lambda_\unp,M_\unp,\du,\dbz$).

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Curvature perturbation spectra from waterfall transition, black hole   constraints and non-Gaussianity

Published Paper #: 363

Authors:, Edgar Bugaev, Peter Klimai,

Journal: JCAP 11 (2011) 028

url: http://arxiv.org/pdf/1107.3754v2.pdf

Abstract: We carried out numerical calculations of a contribution of the waterfall field to the primordial curvature perturbation (on uniform density hypersurfaces) $\zeta$, which is produced during waterfall transition in hybrid inflation scenario. The calculation is performed for a broad interval of values of the model parameters. We show that there is a strong growth of amplitudes of the curvature perturbation spectrum in the limit when the bare mass-squared of the waterfall field becomes comparable with the square of Hubble parameter. We show that in this limit the primordial black hole constraints on the curvature perturbations must be taken into account. It is shown that, in the same limit, peak values of the curvature perturbation spectra are far beyond horizon, and the spectra are strongly non-Gaussian.

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Supersonic baryon-CDM velocities and CMB B-mode polarization

Published Paper #: 362

Authors:, Simone Ferraro, Kendrick M. Smith, Cora Dvorkin,

Journal: Phys. Rev. D 85, 043523 (2012)

url: http://arxiv.org/pdf/1110.2182v1.pdf

Abstract: It has recently been shown that supersonic relative velocities between dark matter and baryonic matter can have a significant effect on formation of the first structures in the universe. If this effect is still non-negligible during the epoch of hydrogen reionization, it generates large-scale anisotropy in the free electron density, which gives rise to a CMB B-mode. We compute the B-mode power spectrum and find a characteristic shape with acoustic peaks at l ~ 200, 400, ... The amplitude of this signal is a free parameter which is related to the dependence of the ionization fraction on the relative baryon-CDM velocity during the epoch of reionization. However, we find that the B-mode signal is undetectably small for currently favored reionization models in which hydrogen is reionized promptly at z ~ 10, although constraints on this signal by future experiments may help constrain models in which partial reionization occurs at higher redshift, e.g. by accretion onto primordial black holes.

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Transient solar oscillations driven by primordial black holes

Published Paper #: 361

Authors:, Michael Kesden, Shravan Hanasoge,

Journal: Phys. Rev. Lett. 107, 111101 (2011)

url: http://arxiv.org/pdf/1106.0011v2.pdf

Abstract: Stars are transparent to the passage of primordial black holes (PBHs) and serve as seismic detectors for such objects. The gravitational field of a PBH squeezes a star and causes it to ring acoustically. We calculate the seismic signature of a PBH passing through the Sun. The background for this signal is the observed spectrum of solar oscillations excited by supersonic turbulence. We predict that PBHs more massive than 10^21 g (comparable in mass to an asteroid) are detectable by existing solar observatories. The oscillations excited by PBHs peak at large scales and high frequencies, making them potentially detectable in other stars. The discovery of PBHs would have profound implications for cosmology and high-energy physics.

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Eccentric Black Hole-Neutron Star Mergers

Published Paper #: 360

Authors:, Branson C. Stephens, William E. East, Frans Pretorius,

Journal: ApJ, 737, L5 (2011)

url: http://arxiv.org/pdf/1105.3175v2.pdf

Abstract: Within the next few years gravitational waves (GWs) from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of these systems a high priority. As an additional motivation, these systems may represent a subset of short-duration gamma-ray burst (sGRB) progenitors. BH-NS mergers are expected to result from primordial, quasi-circular inspiral as well as dynamically formed capture binaries. The latter channel allows mergers with high eccentricity, resulting in a richer variety of outcomes. We perform general relativistic simulations of BH-NS interactions with a range of impact parameters, and find significant variation in the properties of these events that have potentially observable consequences, namely the GW signature, remnant accretion disk mass, and amount of unbound material.

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Effect of Vacuum Energy on Evolution of Primordial Black Holes in   Einstein Gravity

Published Paper #: 359

Authors:, Bibekananda Nayak, Mubasher Jamil,

Journal: Phys. Lett. B Volume 709, Issue 3 (2012)118-122

url: http://arxiv.org/pdf/1107.2025v1.pdf

Abstract: We study the evolution of primordail black holes by considering present universe is no more matter dominated rather vacuum energy dominated. We also consider the accretion of radiation, matter and vacuum energy during respective dominance period. In this scenario, we found that radiation accretion efficiency should be less than 0.366 and accretion rate is much larger than previous analysis by B. Nayak et al. \cite{ns}. Thus here primordial black holes live longer than previous works \cite{ns}. Again matter accretion slightly increases the mass and lifetime of primordial black holes. However, the vacuum energy accretion is slightly complicated one, where accretion is possible only upto a critical time. This critical time depends on the values of accretion efficiency and formation time. If a primordial black hole lives beyond critical time, then its lifespan increases due to vacuum energy accretion. But for presently evaporating primordial black holes, critical time comes much later than their evaporating time and thus vacuum energy could not affect those primordial black holes. We again found that the constraints on the initial mass fraction of PBH obtained from the $\gamma$-ray background limit becomes stronger in the presence of vacuum energy.

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Stochastic Gravitational Wave Background from Coalescing Binary Black   Holes

Published Paper #: 358

Authors:, Xing-Jiang Zhu, Eric Howell, Tania Regimbau, David Blair, Zong-Hong Zhu,

Journal: Astrophys. J., 739, 86 (2011)

url: http://arxiv.org/pdf/1104.3565v3.pdf

Abstract: We estimate the stochastic gravitational wave (GW) background signal from the field population of coalescing binary stellar mass black holes (BHs) throughout the Universe. This study is motivated by recent observations of BH-Wolf-Rayet star systems and by new estimates in the metallicity abundances of star forming galaxies that imply BH-BH systems are more common than previously assumed. Using recent analytical results of the inspiral-merger-ringdown waveforms for coalescing binary BH systems, we estimate the resulting stochastic GW background signal. Assuming average quantities for the single source energy emissions, we explore the parameter space of chirp mass and local rate density required for detection by advanced and third generation interferometric GW detectors. For an average chirp mass of 8.7$M_{\odot}$, we find that detection through 3 years of cross-correlation by two advanced detectors will require a rate density, $r_0 \geq 0.5 \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Combining data from multiple pairs of detectors can reduce this limit by up to 40%. Investigating the full parameter space we find that detection could be achieved at rates $r_0 \sim 0.1 \rm{Mpc}^{-3} \rm{Myr}^{-1}$ for populations of coalescing binary BH systems with average chirp masses of $\sim 15M_{\odot}$ which are predicted by recent studies of BH-Wolf-Rayet star systems. While this scenario is at the high end of theoretical estimates, cross-correlation of data by two Einstein Telescopes could detect this signal under the condition $r_0 \geq 10^{-3} \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Such a signal could potentially mask a primordial GW background signal of dimensionless energy density, $\Omega_{\rm{GW}}\sim 10^{-10}$, around the (1--500) Hz frequency range.

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Gravitational wave background as a probe of the primordial black hole   abundance

Published Paper #: 357

Authors:, Ryo Saito, Jun'ichi Yokoyama,

Journal: Phys.Rev.Lett.102:161101,2009

url: http://arxiv.org/pdf/0812.4339v2.pdf

Abstract: Formation of significant number of primordial black holes (PBHs) is realized if and only if primordial density fluctuations have a large amplitude, which means that tensor perturbations generated from these scalar perturbations as a second order effect are also large and comparable to the observational data. We show that pulsar timing observation could find/rule out PBHs with \sim 10^2 M_solar which are considered as a candidate of intermediate-mass black holes and that PBHs with mass range 10^{20-26} g, which serves as a candidate of dark matter, may be probed by future space-based laser interferometers and atomic interferometers.

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Gravitational-Wave Constraints on the Abundance of Primordial Black   Holes

Published Paper #: 356

Authors:, Ryo Saito, Jun'ichi Yokoyama,

Journal: Prog.Theor.Phys.123:867-886,2010

url: http://arxiv.org/pdf/0912.5317v2.pdf

Abstract: We investigate features of Gravitational Waves (GWs) induced by primordial density fluctuations with a large amplitude peak associated with formation of Primordial Black Holes (PBHs). It is shown that the spectrum of induced GW is insensitive to the width of the peak in wavenumber space provided it is below a certain value, but the amplitude of the spectrum reduces at the peak frequency and decreases faster at low frequencies for a larger width. A correspondence between the GW amplitude and PBH abundance is also investigated incorporating the peak width. We find that PBHs with masses 10^{20-26}g can be probed by space-based laser interferometers and atomic interferometers irrespective of whether the peak width is small or not. Further we obtain constraints on the abundance of the supermassive PBHs by comparing a low frequency tail of the GW spectrum with CMB observations.

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Separate Universes Do Not Constrain Primordial Black Hole Formation

Published Paper #: 355

Authors:, Michael Kopp, Stefan Hofmann, Jochen Weller,

Journal: Phys.Rev.D83:124025,2011

url: http://arxiv.org/pdf/1012.4369v2.pdf

Abstract: Carr and Hawking showed that the proper size of a spherical overdense region surrounded by a flat FRW universe cannot be arbitrarily large as otherwise the region would close up on itself and become a separate universe. From this result they derived a condition connecting size and density of the overdense region ensuring that it is part of our universe. Carr used this condition to obtain an upper bound for the density fluctuation amplitude with the property that for smaller amplitudes the formation of a primordial black hole is possible, while larger ones indicate a separate universe. In contrast, we find that the appearance of a maximum is not a consequence of avoiding separate universes but arises naturally from the geometry of the chosen slicing. Using instead of density a volume fluctuation variable reveals that a fluctuation is a separate universe iff this variable diverges on superhorizon scales. Hence Carr's and Hawking's condition does not pose a physical constraint on density fluctuations. The dynamics of primordial black hole formation with an initial curvature fluctuation amplitude larger than the one corresponding to the maximum density fluctuation amplitude was previously not considered in detail and so we compare it to the well-known case where the amplitude is smaller by presenting embedding and conformal diagrams of both types in dust spacetimes.

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Relic gravitational waves from light primordial black holes

Published Paper #: 354

Authors:, Alexander D. Dolgov, Damian Ejlli,

Journal: Phys.Rev.D84:024028,2011

url: http://arxiv.org/pdf/1105.2303v3.pdf

Abstract: The energy density of relic gravitational waves (GWs) emitted by primordial black holes (PBHs) is calculated. We estimate the intensity of GWs produced at quantum and classical scattering of PBHs, the classical graviton emission from the PBH binaries in the early Universe, and the graviton emission due to PBH evaporation. If nonrelativistic PBHs dominated the cosmological energy density prior to their evaporation, the probability of formation of dense clusters of PBHs and their binaries in such clusters would be significant and the energy density of the generated gravitational waves in the present day universe could exceed that produced by other known mechanisms. The intensity of these gravitational waves would be maximal in the GHz frequency band of the spectrum or higher and makes their observation very difficult by present detectors but also gives a rather good possibility to investigate it by present and future high frequency gravitational waves electromagnetic detectors. However, the low frequency part of the spectrum in the range $f\sim 0.1-10$ Hz may be detectable by the planned space interferometers DECIGO/BBO. For sufficiently long duration of the PBH matter dominated stage the cosmological energy fraction of GWs from inflation would be noticeably diluted.

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Phantom energy accretion and primordial black holes evolution in   Brans-Dicke theory

Published Paper #: 353

Authors:, B. Nayak, L. P. Singh,

Journal: Eur. Phys. J. C 71, 1837 (2011)

url: http://arxiv.org/pdf/1106.2314v1.pdf

Abstract: In this work, we study the evolution of primordial black holes within the context of Brans-Dicke theory by considering the presence of a dark energy component with a super-negative equation of state called phantom energy as a background. Besides Hawking evaporation, here we consider two type of accretions - radiation accretion and phantom energy accretion. We found that radiation accretion increases the lifetime of primordial black holes whereas phantom accretion decreases the lifespan of primordial black holes. Investigating the competition between the radiation accretion and phantom accretion, we got that there is an instant during the matter-dominated era beyond which phantom accretion dominates radiation accretion. So the primordial black holes which are formed in the later part of radiation dominated era and in matter dominated era are evaporated at a quicker rate than the Hawking evaporation. But for presently evaporating primordial black holes, radiation accretion and Hawking evaporation terms are dominant over phantom accretion term and hence presently evaporating primordial black holes are not much affected by phantom accretion.

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Stochastic emergence of inflaton fluctuations in a SdS primordial   universe with large-scale repulsive gravity from a 5D vacuum

Published Paper #: 352

Authors:, Luz Marina Reyes, Jose Edgar Madriz Aguilar, Mauricio Bellini,

Journal: Eur.Phys.J.Plus 126:56,2011

url: http://arxiv.org/pdf/1005.1232v5.pdf

Abstract: We develop a stochastic approach to study scalar field fluctuations of the inflaton field in an early inflationary universe with a black-hole (BH), which is described by an effective 4D SdS metric. Considering a 5D Ricci-flat SdS static metric, we implement a planar coordinate transformation, in order to obtain a 5D cosmological metric, from which the effective 4D SdS metric can be induced on a 4D hypersurface. We found that at the end of inflation, the squared fluctuations of the inflaton field are not exactly scale independent and becomes sensitive with the mass of the BH.

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Evolution of Primordial Stars Powered by Dark Matter Annihilation up to   the Main-Sequence Stage

Published Paper #: 351

Authors:, Shingo Hirano, Hideyuki Umeda, Naoki Yoshida,

Journal: Astrophys.J.736:58-67,2011

url: http://arxiv.org/pdf/1105.1255v1.pdf

Abstract: Primordial stars formed in the early universe are thought to be hosted by compact dark matter (DM) halos. If DM consists of Weakly Interacting Massive Particles (WIMPs), such stars may be powered by DM annihilation during the early phases of their evolutions. We study the pre-main sequence evolutions of the primordial star using a detailed stellar evolution code under the assumption that the annihilation of adiabatically contracted WIMPs DM within the star provides a sufficient energy to sustain the stellar equilibrium. We follow the evolution of accreting stars using several gas mass accretion rates derived from cosmological simulations. We show that the stellar mass becomes very large, up to 900 - 1000 M_sun when the star reaches the main-sequence phase for a reasonable set of model parameters such as DM particle mass and the annihilation cross section. During the dark star phase, the star expands over a thousand solar-radii, while the surface temperature remains below 10^4 K. The energy generated by nuclear reactions is not dominant during this phase. We also study models with different gas mass accretion rates and the DM particle masses. All our models for different DM particle masses pass the dark star phase. The final mass of the dark stars is essentially unchanged for DM mass of m_DM <= 10 GeV. Gravitational collapse of the massive dark stars will leave massive black holes with mass as large as 1000 M_sun in the early universe.

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Preheating after Small-Field Inflation

Published Paper #: 350

Authors:, Philippe Brax, Jean-Francois Dufaux, Sophie Mariadassou,

Journal: Phys.Rev.D83:103510,2011

url: http://arxiv.org/pdf/1012.4656v2.pdf

Abstract: Whereas preheating after chaotic and hybrid inflation models has been abundantly studied in the literature, preheating in small field inflation models, where the curvature of the inflaton potential is negative during inflation, remains less explored. In these models, a tachyonic instability at the end of inflation leads to a succession of exponentially large increases and \emph{decreases} of the inflaton fluctuations as the inflaton condensate oscillates around the minimum of its potential. The net effect is a competition between low-momentum modes which grow and decrease significantly, and modes with higher momenta which grow less but also decrease less. We develop an analytical description of this process, which is analogous to the quantum mechanical problem of tunneling through a volcano-shaped potential. Depending on the parameters, preheating may be so efficient that it completes in less than one oscillation of the inflaton condensate. Preheating after small field inflation may also be followed by a long matter-dominated stage before the universe thermalizes, depending on the energy scale of inflation and the details of the inflaton interactions. Finally, another feature of these models is that the spectrum of the inflaton fluctuations at the end of preheating may be peaked around the Hubble scale. In fact, because preheating starts when the second slow-roll parameter $|\eta|$ becomes of order unity while the first slow-roll parameter $\epsilon$ is still much smaller than one, the universe is still inflating during preheating and the modes amplified by the initial tachyonic instability leave the Hubble radius. This may lead to an abundant production of primordial black holes and gravitational waves with frequencies today which are naturally small enough to fall into the range accessible by high-sensitivity interferometric experiments.

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H.E.S.S. observations of the globular clusters NGC 6388 and M 15 and   search for a Dark Matter signal

Published Paper #: 349

Authors:, HESS Collaboration, A. Abramowski, F. Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, A. Balzer, A. Barnacka, U. Barres de Almeida, A. R. Bazer-Bachi, Y. Becherini, J. Becker, B. Behera, K. Bernlöhr, A. Bochow, C. Boisson, J. Bolmont, P. Bordas, V. Borrel, J. Brucker, F. Brun, P. Brun, T. Bulik, I. Büsching, S. Carrigan, S. Casanova, M. Cerruti, P. M. Chadwick, A. Charbonnier, R. C. G. Chaves, A. Cheesebrough, L. -M. Chounet, A. C. Clapson, G. Coignet, J. Conrad, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O'C. Drury, F. Dubois, G. Dubus, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, A. Fiasson, G. Fontaine, A. Förster, M. Füßling, Y. A. Gallant, H. Gast, L. Gérard, D. Gerbig, B. Giebels, J. F. Glicenstein, B. Glück, P. Goret, D. Göring, S. Häffner, J. D. Hague, D. Hampf, M. Hauser, S. Heinz, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, A. Hoffmann, W. Hofmann, P. Hofverberg, M. Holler, D. Horns, A. Jacholkowska, O. C. de Jager, C. Jahn, M. Jamrozy, I. Jung, M. A. Kastendieck, K. Katarzynski, U. Katz, S. Kaufmann, D. Keogh, D. Khangulyan, B. Khélifi, D. Klochkov, W. Kluzniak, T. Kneiske, Nu. Komin, K. Kosack, R. Kossakowski, H. Laffon, G. Lamanna, D. Lennarz, T. Löhse, A. Lopatin, C. -C. Lu, V. Marandon, A. Marcowith, J. Masbou, D. Maurin, N. Maxted, T. J. L. McComb, M. C. Medina, J. Méhault, R. Moderski, E. Moulin, C. L. Naumann, M. Naumann-Godo, M. de Naurois, D. Nedbal, D. Nekrassov, N. Nguyen, B. Nicholas, J. Niemiec, S. J. Nolan, S. Ohm, J-P. Olive, E. de Oña Wilhelmi, B. Opitz, M. Ostrowski, M. Panter, M. Paz Arribas, G. Pedaletti, G. Pelletier, P. -O. Petrucci, S. Pita, G. Pühlhofer, M. Punch, A. Quirrenbach, M. Raue, S. M. Rayner, A. Reimer, O. Reimer, M. Renaud, R. de los Reyes, F. Rieger, J. Ripken, L. Rob, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, J. Ruppel, F. Ryde, V. Sahakian, A. Santangelo, R. Schlickeiser, F. M. Schöck, A. Schulz, U. Schwanke, S. Schwarzburg, S. Schwemmer, M. Sikora, J. L. Skilton, H. Sol, G. Spengle, L. Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, K. Stycz, I. Sushch, A. Szostek, J. -P. Tavernet, R. Terrier, O. Tibolla3, M. Tluczykont, K. Valerius, C. van Eldik, G. Vasileiadis, C. Venter, J. P. Vialle, A. Viana, P. Vincent, M. Vivier, H. J. Völk, F. Volpe, S. Vorobiov, M. Vorster, S. J. Wagner, M. Ward, A. Wierzcholska, M. Zacharias, A. Zajczyk, A. A. Zdziarski, A. Zech, H. -S. Zechlin,

Journal: Astrophys. J. 735, 12 (2011)

url: http://arxiv.org/pdf/1104.2548v1.pdf

Abstract: Observations of the globular clusters NGC 6388 and M 15 were carried out by the H.E.S.S. array of Cherenkov telescopes for a live time of 27.2 and 15.2 hours respectively. No gamma-ray signal is found at the nominal target position of NGC 6388 and M 15. In the primordial formation scenario, globular clusters are formed in a dark matter halo and dark matter could still be present in the baryon-dominated environment of globular clusters. This opens the possibility of observing a dark matter self-annihilation signal. The dark matter content of the globular clusters NGC 6388 and M 15 is modelled taking into account the astrophysical processes that can be expected to influence the dark matter distribution during the evolution of the globular cluster: the adiabatic contraction of dark matter by baryons, the adiabatic growth of a black hole in the dark matter halo and the kinetic heating of dark matter by stars. 95% confidence level exclusion limits on the dark matter particle velocity-weighted annihilation cross section are derived for these dark matter haloes. In the TeV range, the limits on the velocity-weighted annihilation cross section are derived at the 10-25 cm3 s-1 level and a few 10-24 cm3 s-1 for NGC 6388 and M 15 respectively.

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Running-Mass Inflation Model and Primordial Black Holes

Published Paper #: 348

Authors:, Manuel Drees, Encieh Erfani,

Journal: JCAP 1104:005,2011

url: http://arxiv.org/pdf/1102.2340v3.pdf

Abstract: We revisit the question whether the running-mass inflation model allows the formation of Primordial Black Holes (PBHs) that are sufficiently long-lived to serve as candidates for Dark Matter. We incorporate recent cosmological data, including the WMAP 7-year results. Moreover, we include "the running of the running" of the spectral index of the power spectrum, as well as the renormalization group "running of the running" of the inflaton mass term. Our analysis indicates that formation of sufficiently heavy, and hence long-lived, PBHs still remains possible in this scenario. As a by-product, we show that the additional term in the inflaton potential still does not allow significant negative running of the spectral index.

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Scalar cosmological perturbations from inflationary black holes

Published Paper #: 347

Authors:, Tomislav Prokopec, Paul Reska,

Journal: JCAP 1103:050,2011

url: http://arxiv.org/pdf/1007.3851v2.pdf

Abstract: We study the correction to the scale invariant power spectrum of a scalar field on de Sitter space from small black holes that formed during a pre-inflationary matter dominated era. The formation probability of such black holes is estimated from primordial Gaussian density fluctuations. We determine the correction to the spectrum by first deriving the Keldysh propagator for a massless scalar field on Schwarzschild-de Sitter space. Our results suggest that the effect is strong enough to be tested -- and possibly even ruled out -- by observations.

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Constraints on the induced gravitational wave background from primordial   black holes

Published Paper #: 346

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys.Rev.D83:083521,2011

url: http://arxiv.org/pdf/1012.4697v2.pdf

Abstract: We perform a consistent calculation of primordial black hole (PBH) mass spectrum and second-order induced gravitational wave (GW) background produced from primordial scalar perturbations in radiation era of the early Universe. It is shown that the maximal amplitudes of the second order GW spectrum that can be approached without conflicting with the PBH data do not depend significantly on the shape of primordial perturbation spectrum. The constraints on the GW background obtained in previous works are extended to a wider GW frequency range. We discuss the applicability of the currently available pulsar timing limits for obtaining the constraints on scalar power spectrum and PBH abundance and show that they can be used for strongly constraining the PBH number density in the PBH mass range $\sim (0.03 - 10) M_{\odot}$.

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Accretion, Primordial Black Holes and Standard Cosmology

Published Paper #: 345

Authors:, Bibekananda Nayak, Lambodar Prasad Singh,

Journal: Pramana 76:173-181,2011

url: http://arxiv.org/pdf/0905.3243v2.pdf

Abstract: Primordial Black Holes evaporate due to Hawking radiation. We find that the evaporation time of primordial black holes increase when accretion of radiation is included.Thus depending on accretion efficiency more and more number of primordial black holes are existing today, which strengthens the idea that the primordial black holes are the proper candidate for dark matter.

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Note on nonstationarity and accretion of Primordial Black Holes in   Brans-Dicke theory

Published Paper #: 344

Authors:, Bibekananda Nayak, Lambodar Prasad Singh,

Journal: Phys.Rev.D82:127301,2010

url: http://arxiv.org/pdf/1005.1529v3.pdf

Abstract: We consider the evolution of primordial black holes by including non-stationarity in their formation process and accretion of radiation in Brans-Dicke theory. Specifically, we focus on how $\eta$, the fraction of the horizon mass the black hole comprises capturing nonstationarity, affects the lifetimes of these primordial black holes. Our calculation reveals that the primordial black hole dynamics is controlled by the product $f\eta$ where $f$ is the accretion efficiency. We also estimate the impact of $\eta$ through $f\eta$ on the primordial black holes' initial mass fraction constraint obtained from the $\gamma$-ray background limit.

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The Cosmological QCD Phase Transition Revisited

Published Paper #: 343

Authors:, Simon Schettler, Tillmann Boeckel, Jurgen Schaffner-Bielich,

Journal: Prog.Part.Nucl.Phys.66:266-270,2011

url: http://arxiv.org/pdf/1012.3342v2.pdf

Abstract: The QCD phase diagram might exhibit a first order phase transition for large baryochemical potentials. We explore the cosmological implications of such a QCD phase transition in the early universe. We propose that the large baryon-asymmetry is diluted by a little inflation where the universe is trapped in a false vacuum state of QCD. The little inflation is stopped by bubble nucleation which leads to primordial production of the seeds of extragalactic magnetic fields, primordial black holes and gravitational waves. In addition the power spectrum of cold dark matter can be affected up to mass scales of a billion solar masses. The imprints of the cosmological QCD phase transition on the gravitational wave background can be explored with the future gravitational wave detectors LISA and BBO and with pulsar timing.

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Density perturbations in braneworld cosmology and primordial black holes

Published Paper #: 342

Authors:, Edgar Bugaev, Peter Klimai,

Journal: Phys.Rev.D83:023516,2011

url: http://arxiv.org/pdf/1012.1199v1.pdf

Abstract: We study, by numerical methods, the time evolution of scalar perturbations in radiation era of Randall-Sundrum braneworld cosmology. Our results confirm an existence of the enhancement of perturbation amplitudes (near horizon crossing), discovered recently. We suggest the approximate solution of equations of the perturbation theory in the high energy regime, which predicts that the enhancement factor is asymptotically constant, as a function of scale. We discuss the application of this result for the problem of primordial black hole production in braneworld cosmology.

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Constant surface gravity and density profile of dark matter

Published Paper #: 341

Authors:, H. J. de Vega, N. G. Sanchez,

Journal: Int.J.Mod.Phys.A26:1057-1072,2011

url: http://arxiv.org/pdf/0907.0006v4.pdf

Abstract: Cumulative observational evidence confirm that the surface gravity of dark matter (DM) halo mu_{0 D} = r_0 rho_0 where r_0 and rho_0 are the halo core radius and central density, respectively, is nearly constant and independent of galaxy luminosity for a high number of galactic systems (spirals, dwarf irregular and spheroidals, elliptics) spanning over 14 magnitudes in luminosity and of different Hubble types. Remarkably, its numerical value mu_{0 D} = 140 M_{sun}/pc^2 = (18.6 Mev)^3 is approximately the same (up to a factor of two) in all these systems. First, we present the physical consequences of the independence of mu_{0 D} on r_0: the energy scales as the volume sim r_0^3 while the mass and the entropy scale as the surface ~ r_0^2 and the surface times log r_0, respectively. Namely, the entropy scales similarly to the black-hole entropy but with a much smaller coefficient. Second, we compute the surface gravity and the density profile for small scales from first principles and the evolution of primordial density fluctuations since the end of inflation till today using the linearized Boltzmann-Vlasov equation. The density profile rho_{lin}(r) obtained in this way decreases as r^{-1-n_s/2} for intermediate scales where n_s = 0.964 is the primordial spectral index. This scaling is in remarkable agreement with the empirical behaviour found observationally and in N-body simulations: r^{-1.6\pm 0.4}. The observed value of mu_{0 D} indicates that the DM particle mass m is in the keV scale. The theoretically derived density profiles rho_{lin}(r) turn to be cored for m in the keV scale and they look as cusped for m in the GeV scale or beyond. We consider both fermions and bosons as DM particles decoupling either ultrarelativistically or non-relativistically. Our results do not use any particle physics model and vary slightly with the statistics of the DM particle.

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Primordial SdS universe from a 5D vacuum: scalar field fluctuations on   Schwarzschild and Hubble horizons

Published Paper #: 340

Authors:, Jose Edgar Madriz Aguilar, Mauricio Bellini,

Journal: JCAP 1011:020,2010

url: http://arxiv.org/pdf/1003.1105v4.pdf

Abstract: We study scalar field fluctuations of the inflaton field in an early inflationary universe on an effective 4D Schwarzschild-de Sitter (SdS) metric, which is obtained after make a planar coordinate transformation on a 5D Ricci-flat Schwarzschild-de Sitter (SdS) static metric. We obtain the important result that the spectrum of fluctuations at zeroth order is independent of the scalar field mass $M$ on Schwarzschild scales, while on cosmological scales it exhibits a mass dependence. However, in the first-order expansion, the spectrum depends of the inflaton mass and the amplitude is linear with the Black-Hole (BH) mass $m$.

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Higgs-induced spectroscopic shifts near strong gravity sources

Published Paper #: 339

Authors:, Roberto Onofrio,

Journal: Phys.Rev.D82:065008,2010

url: http://arxiv.org/pdf/1011.3064v1.pdf

Abstract: We explore the consequences of the mass generation due to the Higgs field in strong gravity astrophysical environments. The vacuum expectation value of the Higgs field is predicted to depend on the curvature of spacetime, potentially giving rise to peculiar spectroscopic shifts, named hereafter "Higgs shifts." Higgs shifts could be searched through dedicated multiwavelength and multispecies surveys with high spatial and spectral resolution near strong gravity sources such as Sagittarius A* or broad searches for signals due to primordial black holes. The possible absence of Higgs shifts in these surveys should provide limits to the coupling between the Higgs particle and the curvature of spacetime, a topic of interest for a recently proposed Higgs-driven inflationary model. We discuss some conceptual issues regarding the coexistence between the Higgs mechanism and gravity, especially for their different handling of fundamental and composite particles.

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Black Hole Remnants in the Early Universe

Published Paper #: 338

Authors:, Fabio Scardigli, Christine Gruber, Pisin Chen,

Journal: Phys.Rev.D83:063507,2011

url: http://arxiv.org/pdf/1009.0882v2.pdf

Abstract: We consider the production of primordial micro black holes (MBH) remnants in the early universe. These objects induce the universe to be in a matter-dominated era before the onset of inflation. Effects of such an epoch on the CMB power spectrum are discussed and computed both analytically and numerically. By comparison with the latest observational data from the WMAP collaboration, we find that our model is able to explain the quadrupole anomaly of the CMB power spectrum.

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Primordial Black Holes and a Large Hidden Sector

Published Paper #: 337

Authors:, Xavier Calmet,

Journal: Phys.Rev.D82:087501,2010

url: http://arxiv.org/pdf/1007.2919v2.pdf

Abstract: In this note we point out that primordial black holes could be much shorter lived than usually assumed if there is a large hidden sector of particles that only interacts gravitationally with the particles of the standard model. The observation of the explosion of one of these black holes would severely constrain the energy scale at which gravity becomes strong.

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Mechanism for the Suppression of Intermediate-Mass Black Holes

Published Paper #: 336

Authors:, V. I. Dokuchaev, Yu. N. Eroshenko, S. G. Rubin, D. A. Samarchenko,

Journal: Astronomy Letters, 36, 773 (2010); Pisma v Astronomicheskii
 Zhurnal, 36, 816 (2010)

url: http://arxiv.org/pdf/1010.5325v1.pdf

Abstract: A model for the formation of supermassive primordial black holes in galactic nuclei with the simultaneous suppression of the formation of intermediate-mass black holes is presented. A bimodal mass function for black holes formed through phase transitions in a model with a "Mexican hat" potential has been found. The classical motion of the phase of a complex scalar field during inflation has been taken into account. Possible observational manifestations of primordial black holes in galaxies and constraints on their number are discussed.

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Gamma-rays from ultracompact minihalos: potential constraints on the   primordial curvature perturbation

Published Paper #: 335

Authors:, Amandeep S. Josan, Anne M. Green,

Journal: Phys.Rev.D82:083527,2010

url: http://arxiv.org/pdf/1006.4970v2.pdf

Abstract: Ultracompact minihalos (UCMHs) are dense dark matter structures which can form from large density perturbations shortly after matter-radiation equality. If dark matter is in the form of Weakly Interacting Massive Particles (WIMPs), then UCMHs may be detected via their gamma-ray emission. We investigate how the {\em{Fermi}} satellite could constrain the abundance of UCMHs and place limits on the power spectrum of the primordial curvature perturbation. Detection by {\em Fermi} would put a lower limit on the UCMH halo fraction. The smallest detectable halo fraction, $f_{\rm UCMH} \gtrsim 10^{-7}$, is for $M_{\rm UCMH} \sim 10^{3} M_{\odot}$. If gamma-ray emission from UCMHs is not detected, an upper limit can be placed on the halo fraction. The bound is tightest, $f_{\rm UCMH} \lesssim 10^{-5}$, for $M_{\rm UCMH} \sim 10^{5} M_{\odot}$. The resulting upper limit on the power spectrum of the primordial curvature perturbation in the event of non-detection is in the range $\mathcal{P_R} \lesssim 10^{-6.5}- 10^{-6}$ on scales $k \sim 10^{1}-10^{6} \, {\rm Mpc}^{-1}$. This is substantially tighter than the existing constraints from primordial black hole formation on these scales, however it assumes that dark matter is in the form of WIMPs and UCMHs are not disrupted during the formation of the Milky Way halo.

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Primordial Black Hole as a Source of the Boost Factor

Published Paper #: 334

Authors:, Ryo Saito, Satoshi Shirai,

Journal: Phys.Lett.B697:95-100,2011

url: http://arxiv.org/pdf/1009.1947v1.pdf

Abstract: Primordial black holes (PBHs) accumulate weakly interacting massive particles (WIMPs) around them and form ultracompact minihalos (UCMHs), if the WIMP is a dominant component of the dark matter (DM). In this paper, we discuss that the UCMHs seeded by the PBHs with sub-earth mass enhance the WIMP annihilation in the present Universe and can successfully explain the positron and/or electron excess in cosmic ray observed by PAMELA/Fermi experiments. The signal is very similar to that from a decaying dark matter, which can explain the PAMELA and/or Fermi anomaly without conflict with any constraints as long as the decay mode is proper. In this scenario, the boost factor can be as large as 10^5. In addition, we discuss testability of our scenario by gamma-ray point source and gravitational-wave experiments.

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Astrophysical constraints on primordial black holes in Brans-Dicke   theory

Published Paper #: 333

Authors:, B. Nayak, A. S. Majumdar, L. P. Singh,

Journal: JCAP 1008:039,2010

url: http://arxiv.org/pdf/1002.3472v3.pdf

Abstract: We consider cosmological evolution in Brans-Dicke theory with a population of primordial black holes. Hawking radiation from the primordial black holes impacts various astrophysical processes during the evolution of the Universe. The accretion of radiation by the black holes in the radiation dominated era may be effective in imparting them a longer lifetime. We present a detailed study of how this affects various standard astrophysical constraints coming from the evaporation of primordial black holes. We analyze constraints from the present density of the Universe, the present photon spectrum, the distortion of the cosmic microwave background spectrum and also from processes affecting light element abundances after nucleosynthesis. We find that the constraints on the initial primordial black hole mass fractions are tightened with increased accretion efficiency.

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An update on single field models of inflation in light of WMAP7

Published Paper #: 332

Authors:, Laila Alabidi, Ian Huston,

Journal: JCAP 1008:037,2010

url: http://arxiv.org/pdf/1004.4794v3.pdf

Abstract: In this paper we summarise the status of single field models of inflation in light of the WMAP 7 data release. We find little has changed since the 5 year release, and results are consistent with previous findings. The increase in the upper bound on the running of the spectral index impacts on the status of the production of Primordial Black Holes from single field models. The lower bound on the equilateral configuration of the non-gaussianity parameter is reduced and thus the bounds on the theoretical parameters of (UV) DBI single brane models are weakened. In the case of multiple coincident branes the bounds are also weakened and the two, three or four brane cases will produce a tensor-signal that could possibly be observed in the future.

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Constraints from primordial black hole formation at the end of inflation

Published Paper #: 331

Authors:, Amandeep S. Josan, Anne M. Green,

Journal: Phys.Rev.D82:047303,2010

url: http://arxiv.org/pdf/1004.5347v3.pdf

Abstract: Primordial black hole (PBH) abundance limits constrain the primordial power spectrum, and hence models of inflation, on scales far smaller than those probed by cosmological observations. Single field inflation models which are compatible with all cosmological data can have large enough perturbations on small scales to overproduce PBHs, and hence be excluded. The standard formulae for the amplitude of perturbations do not hold for modes that exit the horizon close to the end of inflation however. We use a modified flow analysis to identify models of inflation where the amplitude of perturbations on small scales is large. For these models we then carry out a numerical evolution of the perturbations and use the PBH constraints on the power spectrum to eliminate models which overproduce PBHs. Significant PBH formation can occur in models in which inflation can continue indefinitely and is ended via a secondary mechanism. We demonstrate that PBHs constrain these types of inflation models and show that a numerical evaluation of the power spectrum decreases the number of otherwise viable models of inflation.

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Primordial Black Holes as Dark Matter: Almost All or Almost Nothing

Published Paper #: 330

Authors:, Brian C. Lacki, John F. Beacom,

Journal: Astrophysical Journal Letters 720 (2010) L67-L71

url: http://arxiv.org/pdf/1003.3466v3.pdf

Abstract: Primordial black holes (PBHs) are expected to accrete particle dark matter around them to form ultracompact minihalos (UCMHs), if the PBHs themselves are not most of the dark matter. We show that if most dark matter is a thermal relic, then the inner regions of UCMHs around PBHs are highly luminous sources of annihilation products. Flux constraints on gamma rays and neutrinos set strong abundance limits, improving previous limits by orders of magnitude. Assuming enough particle dark matter exists to form UCMHs, we find that Omega_PBH <~ 10^-4 (for m_DM c^2 ~ 100 GeV) for a vast range in PBH mass. We briefly discuss the uncertainties on our limits, including those due to the evolution of the UCMH luminosity as it annihilates.

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Test particle motion in the space-time of a Kerr black hole pierced by a   cosmic string

Published Paper #: 329

Authors:, Eva Hackmann, Betti Hartmann, Claus Laemmerzahl, Parinya Sirimachan,

Journal: Phys.Rev.D82:044024,2010

url: http://arxiv.org/pdf/1006.1761v1.pdf

Abstract: We study the geodesic equation in the space-time of a Kerr black hole pierced by an infinitely thin cosmic string and give the complete set of analytical solutions of this equation for massive and massless particles in terms of Mino time that allows to decouple the r- and theta-component of the geodesic equation. The solutions of the geodesic equation can be classified according to the particle's energy and angular momentum, the mass and angular momentum per mass of the black hole. We give examples of orbits showing the influence of the cosmic string. We also discuss the perihelion shift and the Lense-Thirring effect for bound orbits and show that the presence of a cosmic string enhances both effects. Comparing our results with experimental data from the LAGEOS satellites we find an upper bound on the energy per unit length of a string piercing the earth which is approximately 10^{16} kg/m. Our work has also applications to the recently suggested explanation of the alignment of the polarization vector of quasars using remnants of cosmic string decay in the form of primordial magnetic field loops.

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Formation of the seed black holes: a role of quark nuggets?

Published Paper #: 328

Authors:, Xiaoyu Lai, Renxin Xu,

Journal: JCAP 1005:028,2010

url: http://arxiv.org/pdf/0911.4777v4.pdf

Abstract: Strange quark nuggets (SQNs) could be the relics of the cosmological QCD phase transition, and they could very likely be the candidate of cold quark matter if survived the cooling of the later Universe, although the formation and evolution of these SQNs depend on the physical state of the hot QGP (quark-gluon plasma) phase and the state of cold quark matter. We reconsider the possibility of SQNs as cold dark matter, and find that the formation of black holes in primordial halos could be significantly different from the standard scenario. In a primordial halo, the collision between gas and SQNs could be frequent enough, and thus the viscosity acting on each SQN would decrease its angular momentum and make it to sink into the center of the halo, as well as heat the gas. The SQNs with baryon numbers less than $10^{35}$ could assemble in the center of the halo before the formation of primordial stars. A black hole could form by merger of these SQNs, and then its mass could quickly become about $10^3\ M_\odot$ or higher, by accreting the surrounding SQNs or gas. The black holes formed in this way could be the seeds for the supermassive black holes at redshift as high as $z\sim 6$.

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Relativistic Images in Randall-Sundrum II Braneworld Lensing

Published Paper #: 327

Authors:, Amitai Y. Bin-Nun,

Journal: Phys.Rev.D81:123011,2010

url: http://arxiv.org/pdf/0912.2081v2.pdf

Abstract: In this paper, we explore the properties of gravitational lensing by black holes in the Randall-Sundrum II braneworld. We use numerical techniques to calculate lensing observables using the Tidal Reissner-Nordstrom (TRN) and Garriga-Tanaka metrics to examine supermassive black holes and primordial black holes. We introduce a new way tp parameterize tidal charge in the TRN metric which results in a large increase in image magnifications for braneworld primordial black holes compared to their 4 dimensional analogues. Finally, we offer a mathematical analysis that allows us to analyze the validity of the logarithmic approximation of the bending angle for any static, spherically symmetric metric. We apply this to the TRN metric and show that it is valid for any amount of tidal charge.

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