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

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.