Hybrid method for constructing inspiral-merger-ringdown waveforms in scalar-Gauss-Bonnet gravity: scalar waves

Gravitational wave observations allow us to probe gravity in the strong and dynamical field regime. It is necessary to extend the construction of inspiral-merger-ringdown waveform templates to theories beyond General Relativity (GR) to perform accurate tests of gravity. This typically requires numerical relativity (NR) simulations that are computationally expensive and time-consuming. A hybrid approximation method has previously been established during the merger within GR by applying effective-one-body-informed post-Newtonian dynamics and the black hole perturbation theory at the same times in different spatial regions and matching the results at a boundary. We aim to extend this hybrid waveform construction to non-GR theories. We consider scalar Gauss-Bonnet gravity as an example that introduces a scalar field coupled to a quadratic curvature invariant in the action. As a first-step calculation, we model scalar waves that source corrections to gravitational waves within the small coupling approximation. We obtain a hybrid scalar waveform by solving a scalar wave equation with optimized scalar boundary data and potential. We could match NR scalar waveforms for a GW150914-like event with the accuracy of order $10^{-3}$.