Numerical black holes and mergers in dynamical Chern-Simons gravity

In order to test general relativity in the dynamical strong-field regime, we would like to have predictions of gravitational waves from black hole mergers in beyond-GR theories. This is complicated by the fact that most 'corrections' lack a well-posed initial value formulation. Nonetheless by using the decoupling limit (motivated by the EFT paradigm) we have a well-posed system and thus can simulate black holes and binary mergers for certain theories. We focus on dynamical Chern-Simons gravity (dCS) though our methods are generic, and thus applicable to a broad class of theories. These are the first simulations of black hole binaries in dCS and indeed any beyond-GR theory (save for scalar-tensor theory).