New Limits on Lorentz and CPT Symmetry Through 50 Gravitational-Wave Events

Lorentz invariance plays a fundamental role in modern physics. However, tiny violations of Lorentz invariance may arise in some candidate quantum-gravity theories. Using a total of 50 events in the gravitational-wave transient catalogs GWTC-1 and GWTC-2, we perform an analysis of the anisotropic birefringence phenomenon in gravitational waves. The use of multiple events allows us to completely break the degeneracy among gravitational Lorentz-invariance-violation coefficients and globally constrain the coefficient space. Compared to previous results at mass dimensions five and six for the Lorentz-violating operators, we tighten the global limits on 34 coefficients by factors ranging from two to seven.