Constraining the nonstandard propagating gravitational waves in the cosmological background with GWTC-3

TL;DR

This paper uses the spectral siren method on GWTC-3 data to constrain nonstandard gravitational wave propagation, finding results consistent with general relativity and improving previous bounds significantly.

Contribution

It introduces an application of the spectral siren method to GWTC-3 data to constrain the friction term in GW propagation, enhancing bounds on modified gravity effects.

Findings

Constraint on the friction term: $ u = 0.5^{+3.5}_{-2.6}$

Improved bounds over GW170817 by an order of magnitude

Results consistent with general relativity

Abstract

The detection of gravitational waves (GWs) has opened a new window to test the fundamental nature of gravity. We present constraints on the nonstandard propagation of GWs using the spectral siren method applied to binary black hole (BBH) mergers from the third Gravitational-Wave Transient Catalog (GWTC-3). The spectral siren method exploits the redshift distribution of BBHs to probe the cosmic expansion history and break degeneracies between cosmology and modified gravity effects. We focus on the friction term $\nu$ in the nonstandard GW propagation equation, which characterizes the running of the Planck mass. Assuming the standard $\Lambda$CDM cosmology, we find $\nu = 0.5^{+3.5}_{-2.6}$ (median and $90\%$ credible interval), improving upon previous constraints from the bright siren event GW170817 by an order of magnitude. This improvement is due to the higher redshifts of BBHs in GWTC-3, reaching up to $z \sim 1$. Our result suggests that the propagation of GWs is consistent with the predictions of general relativity, placing limits on modified gravity theories that predict a time-varying Planck mass. As the sensitivity of GW detectors improves, the spectral siren method will provide a powerful tool for testing gravity on cosmological scales and probing the physics of the early Universe.