Sound Speed Resonance of the Stochastic Gravitational-Wave Background

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 behavior 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.

Automated summary

A novel mechanism is proposed to test the time variation of gravitational-wave propagation speed based on gravitational wave astronomy. The mechanism suggests that testing the variation of gravitational wave speed can provide potential evidence for new physics beyond general relativity. This mechanism involves studying the energy spectrum of gravitational waves to detect the features of varying gravitational wave speeds.