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

The plunge-merger stage of the binary-black hole coalescence, when bodies' velocities reach a large fraction speed light and gravitational-wave luminosity peaks, provides unique opportunity to probe gravity in dynamical nonlinear regime. How much do predictions general relativity differ from ones other theories for this binary evolution? To address question, we develop parametrized waveform model, within effective-one-body formalism, that allows deviations plunge-merger-ringdown stage. As first step, focus on nonprecessing-spin, quasicircular black binaries. In comparison previous works, each gravitational wave mode, our model can modify, with respect general-relativistic predictions, instant at which amplitude instantaneous frequency time instant, value peak amplitude. We use explore several questions considering both synthetic-data injections two signals. particular, find be constrained about 20% GW150914. Alarmingly, GW200129_65458 shows strong violation relativity. interpret result as false violation, either due systematics (mismodeling spin precession) or data-quality issues depending one's interpretation event. This illustrates models tools investigate systematic errors plain results also vividly demonstrate importance glitch mitigation procedures interpreting tests current observations.