Tests of gravitational-wave birefringence with the open gravitational-wave catalog

We report the results of testing gravitational-wave birefringence using largest population events currently available. Gravitational-wave birefringence, which can arise from effective field theory extension general relativity, occurs when parity symmetry is broken, causing left- and right-handed polarizations to propagate following different equations motion. perform Bayesian inference on 94 reported by 4th-Open Catalog (4-OGC) a parity-violating waveform. find no evidence for violation relativity in vast majority events. However, most massive event, GW190521, second GW191109, show intriguing nonzero birefringence. that probability association between GW190521 possible electromagnetic (EM) counterpart Zwicky Transient Facility (ZTF) increased assuming Excluding energy scale constrained ${M}_{\mathrm{PV}}>0.05\text{ }\text{ }\mathrm{GeV}$ at 90% credible interval, an improvement over previous twelve factor five. discuss implications our modified gravity alternative explanations such as waveform systematics. More detections binary black hole mergers upcoming LIGO/Virgo/KAGRA run will shed light true origin apparent