Evolution of Einstein-scalar-Gauss-Bonnet gravity using a modified harmonic formulation

We present numerical solutions of several spacetimes physical interest, including binary black hole mergers, in shift-symmetric Einstein-scalar-Gauss-Bonnet (ESGB) gravity, and describe our methods for solving the full equations motion, without approximation, general spacetimes. While we concentrate on specific example ESGB, methods, which make use a recently proposed modification to generalized harmonic formulation, should be generally applicable all Horndeski theories gravity (including relativity). demonstrate that these can stably follow formation scalar clouds about initially vacuum non-spinning spinning holes values Gauss-Bonnet coupling approaching maximum value above hyperbolicity theory breaks down spherical symmetry. study collision with hair, finding remains hyperbolic spacetime region exterior horizons similar regime, includes cases where deviations from relativity gravitational radiation is appreciable. Finally, used inspiral merger ESGB gravity. This allows making predictions strong-field non-perturbative confronted wave observations, compared approximate treatments modifications relativity.