Probing primordial black holes with anisotropies in stochastic gravitational-wave background

TL;DR

This paper explores how anisotropies in the stochastic gravitational-wave background can reveal the presence of primordial black holes and distinguish them from astrophysical black holes, especially in the stellar mass range.

Contribution

It introduces the first analysis of angular correlations of anisotropies in the gravitational-wave background from primordial black holes, highlighting their distinguishability from astrophysical sources.

Findings

Anisotropies differ between primordial and astrophysical black hole signals.

Low-frequency regime signals can be differentiated based on anisotropy patterns.

Results are promising for identifying primordial black holes in the stellar mass range.

Abstract

Primordial black holes, if considered to constitute a significant fraction of cold dark matter, trace the inhomogeneous large-scale structure of the Universe. Consequently, the stochastic gravitational-wave background, originating from incoherent superposition of unresolved signals emitted by primordial black hole binaries, is expected to display anisotropies across the sky. In this work, we investigate the angular correlations of such anisotropies for the first time and demonstrate their difference from the analogous signal produced by astrophysical black hole binaries. We carefully evaluate the associated uncertainties due to shot-noise and cosmic variance, and demonstrate that the studied signal in the low-frequency regime can be differentiated from the signal of astrophysical origin. Our results are particularly promising in the stellar mass-range, where the identification of the merger origin has been particularly challenging.