Multi-messenger tests of gravity with weakly lensed gravitational waves

TL;DR

This paper proposes a novel multi-messenger approach combining gravitational wave signals with CMB lensing data to test general relativity's predictions about light and gravitational wave trajectories, enabling high-precision gravity tests with upcoming detectors.

Contribution

It introduces a new GW-CMB-CMB cross-correlation method to robustly test GR predictions using future gravitational wave observations.

Findings

Potential for high signal-to-noise measurements of GR predictions

Ability to distinguish between GR and alternative gravity theories

Framework applicable to upcoming GW detectors like LISA and Einstein Telescope

Abstract

General relativity (GR) predicts concordant trajectories for photons and gravitational waves (GW). We propose a new multi-messenger avenue (GW-CMB-CMB) to prove this aspect of fundamental physics by cross-correlating the GW signal of astrophysical origin with the lensing field derived from the cosmic microwave background (CMB). This new window will allow robust measurement of the prediction from GR with high signal-to-noise and will be able to unveil the true nature of gravity using the GW sources detected by missions such as the Laser Interferometer Space Antenna (LISA), Einstein Telescope and Cosmic Explorer.