Studying Aspects of the Early Universe with Primordial Black Holes (original) (raw)
Related papers
Cosmological constraints on primordial black holes
2019
Primordial Black Holes(PBH) may have formed from collapse of high-density primordial fluctuations in the early Universe. Interest for PBH has been stirred anew by the LIGO detection of gravitational waves from massive black hole mergers which might be of primordial origin. In this thesis, we discuss how primordial fluctuations are produced from vacuum fluctuations, which get stretched out of causal contact by an early inflationary epoch. Later, we discuss the thresholds above which these perturbations could end up in forming black holes once re-entered in causal contact. PBHs are distinct from those black holes of stellar origin precisely because the formation proceed through a top-down accretion of structure. PBHs are expected to form before the recombination era—the moment in the cosmic history when atoms came into being for the first time—thus, defying the mass bounds from the nuclear processes due to the exotic state of primordial matter. Finally, we present current observationa...
Primordial Black Holes in the Very Early Universe
The formation of Primordial Black Holes is a robust prediction of several gravitational theories. Whereas the creation of PBHs was very active in the remote past, such process seem to be very negligible at the present epoch. In this work, we estimate the effects from the radiation surrounding PBHs due to the absorption term in the equations that describe how their masses depend on time. The Hawking radiation contributes with mass loss and the absorption term contributes with gain, but a interesting competition between these terms is analysed. These effects are included in the equations describing PBHs and its mass density as the universe evolves in time and the model is able to describes the evolution of the numerical density of PBHs and the mass evolution and comparisons with cosmological constraints set upper limits in their abundances. Moreover, we evaluate the fraction of PBHs (in terms of the critical density) formed from the high-energy collision of particles before Inflation, when the temperatures were close to Planck values. We consider that the Universe has dimension D, and we evaluate the e-folds number in order get a universe free from such Primordial Black Holes. Finally, the Holographic constraint is used to estimate upper bounds to temperature and mass of PBHs with monochromatic spectrum.
Primordial black hole formation in the early universe: critical behaviour and self-similarity
Classical and Quantum Gravity, 2013
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.
Classical and Quantum Gravity, 2009
Following on after two previous papers discussing the formation of primordial black holes in the early universe, we present here results from an in-depth investigation of the extent to which primordial black hole formation in the radiative era can be considered as an example of the critical collapse phenomenon. We focus on initial supra-horizon-scale perturbations of a type which could have come from inflation, with only a growing component and no decaying component. In order to study perturbations with amplitudes extremely close to the supposed critical limit, we have modified our previous computer code with the introduction of an adaptive mesh refinement scheme. This has allowed us to follow black hole formation from perturbations whose amplitudes are up to eight orders of magnitude closer to the threshold than we could do before. We find that scaling-law behaviour continues down to the smallest black hole masses that we are able to follow and we see no evidence of shock production such as has been reported in some previous studies and which led there to a breaking of the scaling-law behaviour at small black-hole masses. We attribute this difference to the different initial conditions used. In addition to the scaling law, we also present other features of the results which are characteristic of critical collapse in this context.
Primordial Black Holes and Early Cosmology
COSMO-97, 1998
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.
Primordial black holes as a probe of the early universe and a varying gravitational constant
Phase Transitions in the Early Universe Theory and Observations, 2001
We discuss recent developments in the study of primordial black holes, focussing particularly on their formation and quantum evaporation. Such studies can place important constraints on models of the early Universe. An especially interesting development has been the realization that such constraints may be severely modified if the value of the gravitational "constant" G varies with cosmological epoch, a possibility which arises in many scenarios for the early Universe. The nature of the modification depends upon whether the value of G near a black hole maintains the value it had at its formation epoch (corresponding to gravitational memory) or whether it tracks the background cosmological value. This is still uncertain but we discuss various approaches which might help to resolve the issue.
Primordial black holes from the preheating instability
After the end of inflation, the inflaton field oscillates around a local minimum of its potential and decays into ordinary matter. These oscillations trigger a resonant instability for cosmological perturbations with wavelengths that exit the Hubble radius close to the end of inflation. In this paper, we study the formation of Primordial Black Holes (PBHs) at these enhanced scales. We find that the production mechanism can be so efficient that PBHs subsequently dominate the content of the universe and reheating proceeds from their evaporation. Observational constraints on the PBH abundance also restrict the duration of the resonant instability phase, leading to tight limits on the reheating temperature that we derive. We conclude that the production of PBHs during reheating is a generic and inevitable property of the simplest inflationary single-field models, and does not require any fine tuning of the inflationary potential.
Primordial Black Hole Formation in the Matter-Dominated Phase of the Universe
The Astrophysical Journal, 2016
We investigate primordial black hole formation in the matter-dominated phase of the Universe, where nonspherical effects in gravitational collapse play a crucial role. This is in contrast to the black hole formation in a radiation-dominated era. We apply the Zel'dovich approximation, Thorne's hoop conjecture, and Doroshkevich's probability distribution and subsequently derive the production probability β 0 of primordial black holes. The numerical result obtained is applicable even if the density fluctuation σ at horizon entry is of the order of unity. For σ 1, we find a semi-analytic formula β 0 0.05556σ 5 , which is comparable with the Khlopov-Polnarev formula. We find that the production probability in the matter-dominated era is much larger than that in the radiation-dominated era for σ 0.05, while they are comparable with each other for σ 0.05. We also discuss how σ can be written in terms of primordial curvature perturbations.
Physics of Primordial Universe
2003
The physical basis of the modern cosmological inflationary models with baryosynthesis and nonbaryonic dark matter and energy implies such predictions of particle theory, that, in turn, apply to cosmology for their test. It makes physics of early Universe ambiguous and particle model dependent. The study of modern cosmology is inevitably linked with the probe for the new physics, underlying it. The particle model dependent phenomena, such as unstable dark matter, primordial black holes, strong primordial inhomogeneities, can play important role in revealing the true physical cosmology. Such phenomena, having serious physical grounds and leading to new nontrivial cosmological scenarious, should be taken into account in the data analysis of observational cosmology.
Some results on the evolution of primordial black holes
Brazilian Journal of Physics, 2005
We briefly review some recent results related to thermodynamics of semiclassical black holes applied to their primordial formation. Issues on the existence of an influx of ambient particles onto the PBHs, which may help grow them, are addressed. We revisit the integrated flux from evaporated PBHs contributing to the present backgrounds and show that there probe mass scales which are otherwise poorly constrained. Finally the Generalized Second Law of Thermodynamics and the Holographic Principle are combined to show that if some form of the latter holds, strong upper bounds to the mass density of PBHs formed in the early universe may be obtained, especially for inflationary cosmological models. This method is completely independent from those based on the background fluxes and applies to potentially important epochs of PBH formation, resulting in quite strong constraints to Ω pbh .