Constraining high-redshift stellar-mass primordial black holes with next-generation ground-based gravitational-wave detectors

TL;DR

This paper demonstrates that next-generation gravitational-wave detectors can significantly constrain the abundance of stellar-mass primordial black holes by analyzing their merger rate evolution at high redshifts, improving current limits.

Contribution

It introduces a hierarchical Bayesian analysis method to estimate primordial black hole abundance using simulated data from future GW detectors, providing tighter constraints than current limits.

Findings

Projected upper limit on primordial black hole fraction as low as 10^{-5}

Future observations can exclude zero primordial black holes if their abundance exceeds 10^{-4}

Merger rate evolution distinguishes primordial black holes from Population III black holes.

Abstract

The possible existence of primordial black holes in the stellar mass window has received considerable attention because their mergers may contribute to current and future gravitational-wave detections. Primordial black hole mergers, together with mergers of black holes originating from Population~III stars, are expected to dominate at high redshifts ($z\gtrsim 10$). However the primordial black hole merger rate density is expected to rise monotonically with redshift, while Population~III mergers can only occur after the birth of the first stars. Next-generation gravitational-wave detectors such as Cosmic Explorer~(CE) and Einstein Telescope~(ET) can access this distinctive feature in the merger rates as functions of redshift, allowing for a direct measurement of the abundance of the two populations, and hence for robust constraints on the abundance of primordial black holes. We simulate four-months worth of data observed by a CE-ET detector network and perform hierarchical Bayesian analysis to recover the merger rate densities. We find that if the Universe has no primordial black holes with masses of $\mathcal{O}(10M_{\odot})$, the projected upper limit on their abundance $f_{\rm PBH}$ as a fraction of dark matter energy density may be as low as $f_{\rm PBH}\sim \mathcal{O}({10^{-5}})$, about two orders of magnitude lower than current upper limits in this mass range. If instead $f_{\rm PBH}\gtrsim 10^{-4}$, future gravitational wave observations would exclude $f_{\rm PBH}=0$ at the 95\% credible interval.