Tests of Gravitational-Wave Birefringence with the Open Gravitational-Wave Catalog

Kavli Affiliate: Lijing Shao

| First 5 Authors: Yi-Fan Wang, Stephanie M. Brown, Lijing Shao, Wen Zhao,

| Summary:

The routine detection of gravitational-wave events from compact binary
coalescences has allowed precise tests of gravity in strong field, dynamical
field, and high energy regime. In this work, we report the results of testing
gravitational-wave birefringence using compact binary coalescence events from
the 3rd Open Gravitational-wave Catalog (3-OGC). Birefringence, an effect where
the left- and right-handed polarizations of gravitational waves follow
different equations of motion, occurs when the parity symmetry of gravity is
broken. This arises naturally in the effective field theory extension of
general relativity. Using Bayesian inference and state-of-the-art waveform
modeling, we use all events in 3-OGC to constrain the lower limit of the energy
scale at which parity violation effects emerge. Overall we do not find evidence
for a violation of general relativity, and thus we constrain the
parity-violating energy scale to $M_mathrm{PV} > 0.11$ GeV at $90%$
confidence level, which is an improvement over previous results by one order of
magnitude. Intriguingly, we find an outlier, GW190521, that supports the
existence of birefringence over general relativity with a higher
match-filtering signal-to-noise ratio and Bayes factor. The inclusion of
birefringence for GW190521 gives consistent sky location estimation with a
possible electromagnetic counterpart reported Zwicky Transient Facility
(ZTF).However, the inferred $M_mathrm{PV}$ from GW190521 is in tension with
the combined constraints from other events, we thus hypothesize that the
non-zero deviation may be caused by the limitations of the existing waveform
approximants. More gravitational wave detections in the future from compact
binary coalescence will further improve the constraints on birefringence and
shed light on possible systematics for GW190521-type events.

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