  The merger phase of compact binary coalescences is the strongest gravity
regime that can be observed. To test the validity of general relativity (GR) in
strong gravitational fields, we propose a gravitational waveform parameterized
for deviations from GR in the dynamical and nonlinear regime of gravity. Our
fundamental idea is that perturbative modifications to a GR waveform can
capture possible deviations in the merger phase that are difficult to model in
a specific theory of gravity. One of notable points is that our waveform is
physically consistent in the sense that the additional radiative losses of
energy and angular momentum associated with beyond-GR modifications are
included. Our prescription to ensure physical consistency in the whole
coalescence process is expected to be applicable to any deviation from the
standard model of compact binary coalescence, such as the extended models of
gravity or the environmental effects of compact objects, as long as
perturbative modifications are considered. Based on the Fisher analysis and the
compatibility with Einstein-dilaton Gauss-Bonnet waveforms, we show that our
parameterization is a physically-consistent minimal one that captures the
deviations in the nonlinear regime.
