Gravitational Wave Anisotropies from Primordial Black Holes

TL;DR

This paper investigates the anisotropies and non-Gaussian features of the gravitational wave background generated by primordial black holes, providing insights into their potential role as dark matter.

Contribution

It calculates the anisotropies and non-Gaussianity of the gravitational wave background from primordial black holes, considering contributions from formation and propagation effects.

Findings

Significant anisotropy and non-Gaussianity imply primordial black holes are unlikely to account for all dark matter.

The anisotropies depend on the shape of the curvature perturbation's non-Gaussianity.

Propagation effects contribute to the gravitational wave background anisotropies.

Abstract

An observable stochastic background of gravitational waves is generated whenever primordial black holes are created in the early universe thanks to a small-scale enhancement of the curvature perturbation. We calculate the anisotropies and non-Gaussianity of such stochastic gravitational waves background which receive two contributions, the first at formation time and the second due to propagation effects. The former contribution can be generated if the distribution of the curvature perturbation is characterized by a local and scale-invariant shape of non-Gaussianity. Under such an assumption, we conclude that a sizeable magnitude of anisotropy and non-Gaussianity in the gravitational waves would suggest that primordial black holes may not comply the totality of the dark matter.