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Abstract General relativity predicts that gravitational waves are described by two polarization states: the plus + state and cross × state. However, alternate theories of gravity allow up to six polarizations. We employ the gravitational-wave null stream , a linear combination of three or more detectors where the + and × signals add to zero, leaving behind noise and—potentially—gravitational waves in nonstandard polarization states. We develop a Gaussian process model to search for extra polarizations beyond general relativity. Using data from 42 three-detector events from LIGO–Virgo–KAGRA’s third Gravitational-wave Transient Catalog, we find no significant evidence of nonstandard polarization, as the highest natural log Bayes factor, comparing a signal model against a no-signal model, is 1.5, which we show is insignificant when compared with a background distribution. We set 90% credible upper limits on the fractional deviation in gravitational-wave strain, ranging from 0.28 to 11.30 with a median of 1.32.
Cheung et al. (Fri,) studied this question.