Tests of general relativity in the nonlinear regime: a parametrized plunge-merger-ringdown waveform model

Gravitational waves provide a unique opportunity to test gravity in the dynamical and nonlinear regime. We present a parametrized test of general relativity (GR) that introduces generic deviations to the plunge, merger and ringdown stages of binary-black-hole coalescences. The novel feature of the model is that it can capture signatures of beyond-GR physics in the plunge-merger phase. We use the model to provide constraints on the plunge-merger parameters from the analysis of GW150914. Alarmingly, we find that GW200129 shows a strong violation of GR. We interpret this result as a false violation of GR either due to waveform systematics (mismodeling of spin precession) or data-quality issues.