Binary black hole mergers in massive Einstein-scalar-Gauss-Bonnet gravity

We study fully non-linear binary black hole mergers in massive Einstein-scalar-Gauss-Bonnet (EsGB) gravity with a linear Gauss-Bonnet coupling function. In the absence of a well-developed initial data solver for EsGB gravity, we demonstrate that the conventional workaround solution for massless scalar fields results in confined junk radiation that contaminates late-time dynamics in the massive theory. We propose a solution to this problem by suitably modifying the equations of motion at the early stages of the simulation to tame such junk radiation, thereby allowing us to study the dynamics of the scalar field during the process of a black hole merger. This is followed by a preliminary analysis of the frequency content in the ringdown of the scalar and tensor modes. In particular, the quadrupole scalar mode exhibits a rich ringdown structure: while it is dominated by the spin-2 ``contamination'' frequency in the early stages, its late time morphology becomes primarily determined by the scalar mass frequency.