Gravitational Waves: A Test for Modified Gravity

TL;DR

This paper investigates how modified gravity theories alter gravitational wave propagation and their observable effects on cosmic microwave background, using a parametrized approach to distinguish these theories from general relativity.

Contribution

It introduces a parametrized modification to gravitational wave propagation and analyzes its impact on cosmic microwave background observations, providing a model-independent test for modified gravity.

Findings

No significant deviation from general relativity detected

Effects on CMB angular power spectrum analyzed

Degeneracy with tensor mode parameters identified

Abstract

In a modified gravity theory, the propagation equation of gravitational waves will be presented in a non-standard way. Therefore this tenor mode perturbation of time-space, as a complement to the scalar mode perturbation, provides a unique character distinguishing modified gravity from general relativity. To avoid the model-dependent issue, in this paper, we propose a parametrised modification to the propagation of gravitational waves. We show the effects on the angular power spectrum of cosmic microwave background radiation due to the parametrised modification and its degeneracy to the tensor mode power spectrum index $n_t$ and its running $\alpha_t$. At last, we report the current status on the detection of modified gravity through the currently available cosmic observations. Our results show no significant deviation to general relativity.