Sound speed resonance of the stochastic gravitational wave background

TL;DR

This paper introduces a new method to detect variations in gravitational wave speed over cosmic history by identifying resonant peaks in the stochastic GW background spectrum, which could reveal new physics beyond general relativity.

Contribution

It proposes a novel resonance-based mechanism to test the time variation of gravitational wave speed using the stochastic GW background, applicable to various modified gravity theories.

Findings

Resonant peaks in GW spectrum indicate oscillating GW speed.

Current and future GW detectors can potentially observe these peaks.

The mechanism provides a falsifiable test for theories predicting GW speed variation.

Abstract

We propose a novel mechanism to test time variation of the propagation speed of gravitational waves (GWs) in light of GWs astronomy. As the stochastic GWs experience the whole history of cosmic expansion, they encode potential observational evidence of such variation. We report that, one feature of a varying GWs speed is that the energy spectrum of GWs will present resonantly-enhanced peaks if the GWs speed oscillates in time at high-energy scales. Such oscillatory behaviour arises in a wide class of modified gravity theories. The amplitude of these peaks can be at reach by current and forthcoming GWs instruments, hence making the underlying theories falsifiable. This mechanism reveals that probing the variation of GWs speed can be a promising way to search for new physics beyond general relativity.