Imprints of Large-Scale Structures in the Anisotropies of the Cosmological Gravitational Wave Background

TL;DR

This paper investigates how large-scale structures imprint on the anisotropies of the cosmological gravitational wave background (CGWB), proposing methods to detect these signals and use them to probe primordial non-Gaussianity and distinguish cosmological from astrophysical sources.

Contribution

It demonstrates the potential of cross-correlating CGWB anisotropies with galaxy surveys to detect large-scale structure imprints and constrain primordial non-Gaussianity.

Findings

Cross-correlation signal could be detectable with upcoming surveys.

Forecasts suggest constraints on local primordial non-Gaussianity of σ(f_NL^loc)~10.

Combining CGWB and LSS data improves parameter constraints by 4%.

Abstract

We compute the cross-correlation between the anisotropies of the cosmological gravitational wave background (CGWB) and the galaxy density contrast. We show that the cross-correlation is non-zero due to the {\it late} integrated Sachs-Wolfe (ISW) effect experienced by tensor modes. We study the detection prospects of the cross-correlation signal against cosmic variance (CV), and in the light of incoming LSS and GW surveys, where we found that the signal under certain conditions could be distinguishable from noise. In addition, by considering a CGWB sourced by scalar-induced gravitational waves, and the inclusion of a scale-dependent galaxy bias, we use the cross-correlation to forecast local primordial non-Gaussianity, where we find $\sigma(f_\text{NL}^\text{loc})\sim10$ for CV only and a LSST-like survey. Moreover, by combining the Fisher information of CGWB$\times$LSS with LSS, we are able to improve the constraints by 4\% compared to an LSS-only analysis. Our results imply that a cross-correlation between GW anisotropies and LSS can indeed come from a stochastic background of cosmological origin and could be used to distinguish it from an astrophysical one.