PBH formation from overdensities in delayed vacuum transitions

TL;DR

This paper explores how inhomogeneities in vacuum energy decay during first-order phase transitions can seed primordial black holes, with their mass and abundance influenced by nucleation dynamics, potentially explaining observed microlensing events.

Contribution

It introduces a detailed analysis of PBH formation from vacuum decay in FOPTs, linking nucleation dynamics to PBH abundance and mass, and explores observational implications.

Findings

PBHs can form in generic FOPTs due to vacuum energy inhomogeneities.

The PBH mass is set by the Hubble mass, while their number density depends on nucleation.

Populations of PBHs are generated in mass ranges relevant for microlensing observations.

Abstract

Primordial black hole (PBH) formation from first-order phase transitions (FOPTs) combines two prevalent elements of beyond the Standard Model physics with wide-ranging consequences. We elaborate on a recently proposed scenario in which inhomogeneities in vacuum energy decay seed the overdensities that collapse to PBHs. In this scenario, the PBH mass is determined by the Hubble mass as in conventional formation scenarios, while its number density is determined by the nucleation dynamics of the FOPT. We present a detailed study of the formation probability including parameter dependencies. In addition, we generate populations in the open mass window as well as for the HSC and OGLE candidate microlensing events. This mechanism inevitably creates PBHs in generic FOPTs, with significant populations produced in slow and moderately strong phase transitions.