Primordial Black Holes from First-Order Cosmological Phase Transitions

TL;DR

This paper explores a novel mechanism for primordial black hole formation during first-order cosmological phase transitions, involving particle transmission suppression and overdensity buildup, quantified through Boltzmann equation analysis.

Contribution

It introduces a new process linking phase transition dynamics and black hole formation, with detailed quantitative modeling of particle behavior and conditions needed for significant black hole production.

Findings

Overdensity formation can lead to primordial black holes during phase transitions.

Boltzmann equation solutions quantify conditions for black hole formation.

Phase transition properties influence black hole abundance.

Abstract

We discuss the possibility of forming primordial black holes during a first-order phase transition in the early Universe. As is well known, such a phase transition proceeds through the formation of true-vacuum bubbles in a Universe that is still in a false vacuum. When there is a particle species whose mass increases significantly during the phase transition, transmission of the corresponding particles through the advancing bubble walls is suppressed. Consequently, an overdensity can build up in front of the walls and become sufficiently large to trigger primordial black hole formation. We track this process quantitatively by solving a Boltzmann equation, and we delineate the phase transition properties required for our mechanism to yield an appreciable abundance of primordial black holes.