Primordial black holes from bubble collisions during a first-order phase transition

TL;DR

This paper investigates the formation of primordial black holes from bubble collisions during a first-order phase transition, highlighting the conditions, uncertainties, and potential cosmological implications of PBH production.

Contribution

It introduces parameters to model bubble collision uncertainties and estimates PBH abundance, showing that such transitions can produce significant PBHs affecting dark matter and universe evolution.

Findings

PBHs can form from bubble collisions with thick fluid shells

The PBH mass spectrum is approximately monochromatic

Certain parameter regions allow PBHs to account for or overclose dark matter

Abstract

We study the possibility of production of primordial black holes (PBHs) from bubble collisions during a first-order phase transition. While typical colliding bubbles are small and irrelevant for PBH production, we find that those that can produce PBHs must have a macroscopically thick fluid shell and have been born much before the typical nucleation time. Particularly large uncertainties arise from an exponential sensitivity of the nucleation rate on the required duration of bubble growth which depends on the details of the collisions and the evolution of the spacetime metric toward the end of the phase transition. We introduce a few parameters to be obtained from future numerical simulation to represent those unknowns, and estimate the PBH abundance in an Abelian Higgs benchmark model and show that it can be significant. We predict an approximately monochromatic PBH mass spectrum, and find regions in the parameter space where the PBHs can constitute entire dark matter or even over-close the universe. Our result thus shows that models with a first-order phase transition can be constrained by over-abundant PBHs or null results of other PBH searches.