Approximate inspiral-merger-ringdown waveforms for binary-black-hole mergers in extensions of general relativity

Gravitational-wave tests of general relativity (GR) rely on gravitational waveform models which are produced in either a specific modified theory of gravity or which are generated in a more theory-agnostic framework [often by adding a set of deviation parameters to some (semi-)analytical waveform family that reduces to the GR waveform when the parameters are set to zero]. Generating theory-specific inspiral-merger-ringdown (IMR) waveforms can be computationally intensive, but they give definite predictions for the modified theory. Theory-agnostic waveforms are often much faster to generate, but they do not necessarily correspond to a waveform that would be produced in any specific extension of GR. We describe an adaptation to modified theories of gravity of a hybrid post-Newtonian and black-hole perturbation method that was used in GR to explain the qualitative features and physics of binary-black-hole mergers. The method could be used to generate approximate IMR waveforms in extensions of GR, to explain their qualitative features, or to tailor the parameter space of theory-agnostic waveforms to better match those from specific extensions of GR.