Gravitational wave friction in light of GW170817 and GW190521

TL;DR

This paper uses gravitational wave events GW170817 and GW190521 to test and constrain theories of gravity beyond General Relativity, focusing on modifications affecting GW propagation and luminosity distance.

Contribution

It introduces a framework to constrain beyond-GR models using GW data, improving bounds on spacetime dimensions and gravitational constant variation.

Findings

Constraints on spacetime dimensions compatible with 4 at 2.5% precision

Upper limit on Newton's constant variation <20% at GW epoch

Improved GR deviation parameters constraints with GW190521 inclusion

Abstract

We use the gravitational wave (GW) events GW170817 and GW190521, together with their proposed electromagnetic counterparts, to constrain cosmological parameters and theories of gravity beyond General Relativity (GR). In particular we consider models with a time-varying Planck mass, large extra-dimensions, and a phenomenological parametrization covering several beyond-GR theories. In all three cases, this introduces a friction term into the GW propagation equation, effectively modifying the GW luminosity distance. We set constraints on $\Lambda$CDM parameters and GR deviation parameters using two sets of priors on the Hubble constant and matter energy density. With priors set to the measured Planck's mission values, we find that with the inclusion of GW190521, the two GR deviation parameters constraints improves by a factor $\sim 10$, we report a number of spacetime dimensions compatible with $4$ with an precision of $2.5\%$ (at 95\% CL) and an upper limit to the variation of Netwon's constant at the epoch of GW170817 $<20\%$. With wide priors on the Hubble constant and matter energy density, we show that it is still possible to constrain the $\Lambda$CDM parameters and GR deviation parameters conjointly from GW170817 and GW190521 obtaining constraints on GR deviation parameters which are a factor $2-6$ worse than the results using restricted priors on $\Lambda$CDM parameters.