Primordial Black Hole Formation in a Dust Bouncing Model

TL;DR

This paper investigates the potential formation of primordial black holes during a dust-dominated contracting phase in bouncing cosmological models, finding that such black holes are unlikely to account for dark matter.

Contribution

It provides a detailed analysis of perturbation collapse conditions in a flat-dust bounce model using a parametric solution and explores the implications for primordial black hole formation.

Findings

Primordial black hole formation is unlikely to produce a significant dark matter component.

Newtonian gauge is inadequate for describing perturbations in contracting models.

Numerical calculations of perturbation spectra support the conclusion.

Abstract

Linear scalar cosmological perturbations have increasing spectra in the contracting phase of bouncing models. We study the conditions for which these perturbations may collapse into primordial black holes and the hypothesis that these objects constitute a fraction of dark matter. We compute the critical density contrast that describes the collapse of matter perturbations in the flat-dust bounce model with a parametric solution, obtained from the Lemaitre-Tolman-Bondi metric that represents the spherical collapse. We discuss the inability of the Newtonian gauge to describe perturbations in contracting models as the perturbative hypothesis does not hold in such cases. We carry the calculations for a different Gauge choice and compute the perturbations power spectra numerically. Finally, assuming a Gaussian distribution, we compute the primordial black hole abundance with the Press-Schechter formalism and compare it with observational constraints. From our analysis, we conclude that the primordial black hole formation in a dust-dominated contracting phase does not lead to a significant mass fraction of primordial black holes in dark matter today.