A new mechanism for primordial black hole formation during reheating

TL;DR

This paper proposes a novel mechanism for primordial black hole formation during the reheating era after inflation, involving gravitational collapse of virialized structures of scalar fields, with implications for low-mass PBH abundance.

Contribution

It introduces a new formation process for PBHs during reheating, analyzing collapse thresholds for scalar field structures, including self-interacting cases.

Findings

Collapse thresholds depend on scalar field properties.

Primordial black holes can form from virialized structures during reheating.

Results impact the expected abundance of low-mass PBHs.

Abstract

The Reheating process at the end of inflation is often modeled by an oscillating scalar field which shows a background dust-like behaviour, prompting the analysis of gravitational collapse and black hole formation in this era to be approached by the spherical collapse of standard structure formation. In the scalar field dark matter structure formation process virialized halos halt the direct collapse, resulting in halos with condensed central cores at the de Broglie scale of the dominant scalar field. We show that a similar process can take place during reheating, leading to the formation of primordial black holes (PBHs). We study the formation of PBHs through the gravitational further collapse of structures virialized during reheating, looking at the collapse of either the whole structure, or that of the central core within these configurations. We compute the threshold amplitude for the density contrast to undergo this process, for both free and self-interacting scalar fields. We discuss the relevance of our results for the abundance of PBHs at the lower end of the mass spectrum.