Primordial black holes as dark matter: Interferometric tests of phase transition origin

TL;DR

This paper predicts that primordial black holes formed during a first order phase transition could produce detectable gravitational wave backgrounds, providing a new way to test dark matter models involving black holes.

Contribution

It demonstrates that gravitational wave detectors can observe signals from primordial black holes formed via late nucleating patches in a phase transition, independent of specific models.

Findings

Upcoming interferometers will detect a stochastic gravitational wave background from bubble collisions.

Primordial black holes in the allowed mass window can constitute dark matter.

The gravitational wave signal is robust across different models of phase transitions.

Abstract

We show that primordial black holes - in the observationally allowed mass window with $f_{\rm pbh}=1$ - formed from late nucleating patches in a first order phase transition imply upcoming gravitational wave interferometers will see a large stochastic background arising from the bubble collisions. As an example, we use a classically scale invariant $B-L$ model, in which the right handed neutrinos explain the neutrino masses and leptogenesis, and the dark matter consists of primordial black holes. The conclusion regarding the gravitational waves is, however, expected to hold model independently for black holes coming from such late nucleating patches.