Primordial black holes (PBHs) are a profound signature of primordial cosmological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to restrict a wide range of particle physics models, predicting an enhancement of the ultraviolet part of the spectrum of density perturbations, early dust-like stages, first order phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflationary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds.
We consider the possibility that massive primordial black holes are the dominant form of dark matter. Black hole formation generates entropy fluctuations that adds a Poisson noise to the matter power spectrum. We use Lyman-alpha forest observations to constrain this Poisson term in matter power spectrum, then we constrain the mass of black holes to be less than few times 10^4 solar mass. We also find that structures with less than ~ 10^3 primordial black holes evaporate by now.
Can a violent process like sudden reheating after supercooling at the onset of a first-order QCD transition improve the possibility of primordial black hole formation? Underdensities reheat earlier than overdensities, there is a short period of huge pressure differences, hence fluid acceleration. Density perturbations on scales far below the Hubble radius $λ\ll R_{\rm H} $ get an amplification which grows quadratically in wavenumber, the amplifications at the horizon scale are small. Primordial black hole formation cannot be sufficiently amplified by the QCD transition unless the initial spect…
We propose a scenario in which the cosmological domain wall and monopole problems are solved without any fine tuning of the initial conditions or parameters in the Lagrangian of an underlying filed theory. In this scenario domain walls sweep out (unwind) the monopoles from the early universe, then the fast primordial black holes perforate the domain walls, change their topology and destroy them. We find further that the (old vacuum) energy density released from the domain walls could alleviate but not solve the cosmological flatness problem.
We investigate the influence of hadron injection from evaporating primordial black holes (PBHs) in the early stage of the primordial nucleosynthesis era (t = 10^{-3} - 10^4 sec). The emitted quark-antiquark pairs or gluons immediately fragment into a lot of hadrons and scatter off the thermal plasma which is constituted by photons, electrons and nucleons. For the relatively low mass holes we point out that the dominant effect is the inter-conversion between ambient proton and neutron through the strong interaction induced by the emitted hadrons. Even after the freeze-out time of the week inter…
We determine the abundance of primordial black holes (PBHs) formed in the context of non-gaussian models with primordial density perturbations. We consider models with a renormalized $χ^2$ probability distribution function parametrized by the number, $ν$, of degrees of freedom. We show that if $ν$ is not too large then the PBH abundance will be altered by several orders of magnitude with respect to the standard gaussian result obtained in the $ν\to \infty$ limit. We also study the dependence of the spectral index constraints on the nature of the cosmological perturbations for a power-law primo…
Primordial black holes with a narrow mass range are regarded as a nonrelativistic fluid component with an equation of state for dust. The impact of the black hole evaporation on the dynamics of the early universe is studied by resorting to a two-fluid model. We find periods of intense radiation reheating in the initial and final stages of the evaporation.
It was recently shown that the vanishing of the Coulomb field related to the electric charge of a black hole by virtue of a tiny but non-vanishing photon mass can produce an electric asymmetry in the universe. This process can have place both at a cosmological early stage, through primordial black holes, and in contemporary universe, by means of supermassive black holes at galactic centers. Possible consequences of the latter case about the role of electrogenesis in the generation of magnetic fields coherent on galactic scale have been investigated. In this paper we will discuss the electrogen…
We calculate the constraints on the primordial curvature perturbation at the end of inflation from the present day abundance of Primordial Black Holes (PBHs), as a function of the reheat temperature T_{\rm RH}. We first extend recent work on the formation of PBHs on scales which remain within the horizon during inflation and calculate the resulting constraints on the curvature perturbation. We then evaluate the constraint from PBHs that form, more conventionally, from super-horizon perturbations. The constraints apply for T_{\rm RH} < 10^{8} GeV and the inclusion of sub-horizon PBHs leads to a…
The observational evidence for a population of quasars powered by supermassive black holes of mass \geq 10^9 M_sun at redshifts z\geq 6 poses a great challenge for any model describing the formation of galaxies. Assuming uninterrupted accretion at the Eddington limit, seed black holes of at least 1000 M_sun are needed at z \approx 15. Here I study whether these seeds could be primordial black holes (PBHs) which have been produced in the very early universe by the collapse of primordial density fluctuations. In particular, I study the expected number densities of PBHs in the relevant mass range…
Primordial black holes (PBHs) are known to be produced from collapsing cosmic defects such as domain walls and strings. In this paper we show how PBHs are produced in monopole-string networks.
The evolution of the primordial low mass black hole (PBH) in hot universe is considered. Increase of mass and decrease of PBH spin due to the accretion of radiation dominated matter are estimated with using of results of numerical simulation of PBH formation and approximate relations for accretion to a rotating black hole.
The mass function of primordial black holes created through the near-critical gravitational collapse is calculated in a manner fairly independent of the statistical distribution of underlying density fluctuation, assuming that it has a sharp peak on a specific scale. Comparing it with various cosmological constraints on their mass spectrum, some newly excluded range is found in the volume fraction of the region collapsing into black holes as a function of the horizon mass.
A consequence of the evaporation of primordial black holes in the early universe may be the generation of mirror matter. This would have implications with regard to dark matter, and the number of light particle species in equilibrium at the time of big bang nucleosynthesis. The possibilities for the production of mirror matter by this mechanism are explored.
A perturbative analysis shows that black holes do not remember the value of the scalar field $ϕ$ at the time they formed if $ϕ$ changes in tensor-scalar cosmology. Moreover, even when the black hole mass in the Einstein frame is approximately unaffected by the changing of $ϕ$, in the Jordan-Fierz frame the mass increases. This mass increase requires a reanalysis of the evaporation of primordial black holes in tensor-scalar cosmology. It also implies that there could have been a significant magnification of the (Jordan-Fierz frame) mass of primordial black holes.
Antiprotons and antideuterons are considered as probes to look for primordial black holes in our Galaxy. I give a brief overview of the latest developments on the subject.
Probability for a primordial black hole to invade the Kuiper belt was calculated. We showed that primordial black holes of certain masses can significantly change asteroids' orbits. These events may result in disasters, local for our solar system and global for the Earth (like the Tunguska meteorite). We also estimated how often such events occur.
We discuss the hypothesis that the cosmological baryon asymmetry and entropy were produced in the early Universe by the primordial black hole (PBHs) evaporation.
We describe a mechanism of the primordial black holes formation that can explain the existence of a population of supermassive black holes in galactic bulges. The mechanism is based on the formation of black holes from closed domain walls. The origin of such domain walls could be a result of the evolution of an effectively massless scalar field during inflation. The initial non-equilibrium distribution of the scalar field imposed by background de-Sitter fluctuations gives rise to the spectrum of black holes, which covers a wide range of masses -- from superheavy ones down to deeply subsolar. T…
We describe the changes to the standard primordial black hole constraints on density perturbations if there are modifications to the standard cosmology between the time of formation and nucleosynthesis.
The production of Primordial Black Holes (PBH) from inflationary perturbations provides a physical process where the effective classicality of the fluctuations does not hold for certain scales. For adiabatic perturbations produced during inflation, this range of scales corresponds to PBH with masses $M\ll 10^{15}$ g. For PBH with masses $M\sim M_H(t_e)$, the horizon mass at the end of inflation, the generation process during the preheating stage could be classical as well, in contrast to the formation of PBH on these scales by adiabatic inflationary perturbations. For the non evaporated PBH, t…
As a nonbaryonic explanation of massive compact halo objects, a phenomenological model is presented which predicts formation of primordial black holes at a desired mass scale. The required feature of initial density fluctuation is realized making use of the primordially isocurvature fluctuation generated in an inflationary universe model with multiple scalar fields.
We review some of the expectations for Primordial Black Hole evaporation and we review the properties of short Gamma Ray Bursts. It is plausible that these GRB come from PBH evaporation. We then show that the angular distribution asymmetry recently observed by us could be due to a concentration of PBH in the Galactic Arms like the Orion arm.
Black hole formation in the framework of hybrid inflation is considered. It is shown that this model of inflation provides conditions for multiple black hole production.
A population of very light primordial black holes which evaporate before nucleosynthesis begins is unconstrained unless the decaying black holes leave stable relics. We show that gravitons Hawking radiated from these black holes would source a substantial stochastic background of high frequency gravititational waves ($10^{12}$ Hz or more) in the present universe. These black holes may lead to a transient period of matter dominated expansion. In this case the primordial universe could be temporarily dominated by large clusters of "Hawking stars" and the resulting gravitational wave spectrum is …
If the cosmological dark matter has a component made of small primordial black holes, they may have a significant impact on the physics of the first stars and on the subsequent formation of massive black holes. Primordial black holes would be adiabatically contracted into these stars and then would sink to the stellar center by dynamical friction, creating a larger black hole which may quickly swallow the whole star. If these primordial black holes are heavier than $\sim 10^{22} {\rm g}$, the first stars would likely live only for a very short time and would not contribute much to the reioniza…
It is shown that, contrary to the widespread opinion, particle collisions considerably increase accretion rate from the cosmological background onto 5D primordial black holes formed during the high-energy phase of the Randall-Sundrum Type II braneworld scenario. Increase of accretion rate leads to much tighter constraints on initial primordial black hole mass fraction imposed by the critical density limit and measurements of high-energy diffuse photon background and antiproton excess.
We consider the simple inflationary model with peculiarity in the form of "plateau" in the inflaton potential. We use the formalism of coarse-grained field to describe the production of metric perturbations $h$ of an arbitrary amplitude and obtain non-Gaussian probability function for such metric perturbations. We associate the spatial regions having large perturbations $h\sim 1$ with the regions going to primordial black holes after inflation. We show that in our model the non-linear effects can lead to overproduction of the primordial black holes.
Model of supermassive black holes formation inside the clusters of primordial black holes is developed. Namely, it is supposed, that some mass fraction of the universe ~10^-3 is composed of the compact clusters of primordial (relic) black holes, produced during phase transitions in the early universe. These clusters are the centers of dark matter condensation. We model the formation of protogalaxies with masses about 2*10^8M_sun at the redshift z=15. These induced protogalaxies contain central black holes with mass ~10^5M_sun and look like dwarf spheroidal galaxies with central density spike. …
We reconsider the possibility that the observed baryon asymmetry was generated by the evaporation of primordial black holes that dominated the early universe. We present a simple derivation showing that the baryon asymmetry is insensitive to the initial black hole density and the cosmological model but is sensitive to the temperature-dependence of the CP and baryon-violating (or lepton-violating) interactions. We also consider the possibility that black holes stop evaporating and form Planck-mass remnants that act as dark matter. We show that primordial black holes cannot simultaneously accoun…
