# Anisotropies and non-Gaussianity of the Cosmological Gravitational Wave Background

## TL;DR

This paper investigates the anisotropies and non-Gaussian features of the cosmological stochastic gravitational wave background, offering new insights into early universe physics and potential for probing primordial non-Gaussianity.

## Contribution

It introduces a Boltzmann approach to analyze GW anisotropies and proposes a novel method to characterize non-Gaussianity in the SGWB, linking it to primordial cosmological perturbations.

## Key findings

- Anisotropies depend on frequency due to production and propagation effects.
- New method to detect deviations from Gaussianity in the SGWB.
- SGWB anisotropies can reveal information about early universe conditions.

## Abstract

The Stochastic Gravitational Wave Background (SGWB) is expected to be a key observable for Gravitational Wave (GW) interferometry. Its detection will open a new window on early universe cosmology and on the astrophysics of compact objects. Using a Boltzmann approach, we study the angular anisotropies of the GW energy density, which is an important tool to disentangle the different cosmological and astrophysical contributions to the SGWB. Anisotropies in the cosmological background are imprinted both at its production, and by GW propagation through the large-scale scalar and tensor perturbations of the universe. The first contribution is not present in the Cosmic Microwave Background (CMB) radiation (as the universe is not transparent to photons before recombination), causing an order one dependence of the anisotropies on frequency. Moreover, we provide a new method to characterize the cosmological SGWB through its possible deviation from a Gaussian statistics. In particular, the SGWB will become a new probe of the primordial non-Gaussianity of the large-scale cosmological perturbations.