A search for extra polarisations using a Gaussian process in Gravitational-Wave Transient Catalogue 3

TL;DR

This paper develops a Gaussian process method to search for non-standard gravitational-wave polarizations using data from LIGO-Virgo-KAGRA, finding no evidence but setting upper limits on deviations from general relativity.

Contribution

The paper introduces a novel Gaussian process approach to detect extra gravitational-wave polarizations beyond general relativity.

Findings

No evidence of non-standard polarizations was found.

Upper limits on fractional deviations were set, as low as 0.39 at 90% credibility.

Method applied successfully to 42 events from GWTC-3.

Abstract

General relativity predicts that gravitational waves are described by two polarisation states: the plus $+$ state and cross $\times$ state. However, alternate theories of gravity allow up to six polarisations. We employ the gravitational-wave null stream, a linear combination of three or more detectors where the $+$ and $\times$ signals add to zero, leaving behind noise and potentially gravitational waves in non-standard polarisation states. We develop a Gaussian process model to search for extra polarisations beyond general relativity. Using data from 42 three-detector events from LIGO-Virgo-KAGRA's Third Gravitational-Wave Transient Catalogue, we find no evidence of non-standard polarisations. We set upper limits on the fractional deviation in gravitational-wave strain to be as low as 0.39 at 90% credibility for the event GW190602_175927.