Gravitational wave signatures of primordial black hole accretion during early matter domination

TL;DR

This paper explores how primordial black holes formed after inflation can grow significantly during early matter domination, producing a distinctive gravitational wave spectrum with two peaks detectable by future GW observatories.

Contribution

It introduces a model of PBH growth during early matter domination and predicts a unique GW spectrum with two observable peaks, linking PBH formation and accretion to GW signals.

Findings

PBHs can grow by up to two orders of magnitude during EMD.

The GW spectrum features two peaks corresponding to different phases.

Detectable GW signals are possible for PBHs in the asteroid mass range.

Abstract

We present a scenario in which primordial black holes (PBHs) form in a post-inflationary radiation-dominated (RD) phase and then experience significant accretion during a phase of early matter dominated (EMD). We show that PBH masses could grow by up to two orders of magnitude. Restricting to the linear perturbation regime, we compute the gravitational wave (GW) spectrum that features two peaks. The high-frequency peak is associated with the PBH formation in the RD phase, while the low-frequency peak is due to the sudden transition from EMD to the later, standard RD phase. We identify a PBH mass range where one or both peaks can be observed by a combination of different GW detectors. Finally, we show the signal-to-noise ratio of the total GW spectrum for PBHs in the asteroid mass window, where they could comprise the totality of dark matter.