Illuminating the Dark Sector: Understanding Modified Gravity Signatures with Cross-Correlations of Gravitational Waves and Large-Scale Structure

TL;DR

This paper explores how combining large-scale structure surveys with gravitational wave observations can improve tests of modified gravity theories, offering a new multi-messenger approach to fundamental physics.

Contribution

It introduces a forecast methodology for LSS-GW cross-correlation signals and demonstrates their potential to tighten constraints on deviations from General Relativity.

Findings

Cross-correlation enhances constraints on modified gravity.

Future GW detectors can significantly improve existing bounds.

Combining LSS and GW data opens new avenues for cosmological tests.

Abstract

We investigate the synergy between large-scale structure (LSS) observations and gravitational wave (GW) events for testing modified gravity. In particular, we forecast the LSS $\times$ GW cross-correlation signal using Stage-IV LSS surveys, such as Euclid, in combination with future detections from the Einstein Telescope. This cross-correlation provides a novel probe of fundamental physics, potentially revealing deviations from the $\Lambda$CDM paradigm that may not be accessible through electromagnetic observations alone. We describe the considered modified gravity scenarios, the relevant LSS and GW observables, and the synthetic forecast methodology. Our results demonstrate that combining LSS and GWs can significantly enhance constraints on departures from General Relativity, opening a new window for multi-messenger cosmology. We further assess the observational requirements GW experiments must meet to improve upon constraints obtainable from LSS alone.