Polarization of gravitational waves in symmetric teleparallel theories of gravity and their modifications

TL;DR

This paper investigates gravitational wave polarization and speed in various symmetric teleparallel gravity theories, revealing that some models predict deviations from general relativity, including new polarizations and different propagation speeds.

Contribution

It systematically analyzes GW properties in extended symmetric teleparallel gravity theories, identifying conditions for deviations from general relativity.

Findings

General relativity-like GW speed and polarization in simple and generalized STG

Scalar-non-metricity theories exhibit different GW speeds

f(Q,B) gravity introduces new GW polarizations

Abstract

Symmetric teleparallel gravity (STG) offers an interesting avenue to formulate a theory of gravitation that relies neither on curvature nor torsion but only on non-metricity Q. Given the growing number of observations of gravitational waves (GWs) and their use to explore gravitational theories, in this work we investigate the GWs in various extensions of STG, focusing on their speed and polarization. For the simple STG, for theories that arise from the generalized irreducible decomposition of STG, and for f(Q) gravity, we obtain the same speed and polarizations with general relativity. For scalar - non-metricity theories, where a scalar field is nonminimally coupled to f(Q), we find that GWs propagate in general with a speed different than the one of light. Finally, for the case of f(Q,B) gravity we find that new polarizations do appear.