Testing the predictions of general relativity in the dynamical strong-field regime, in particular black holes and their dynamics, has only recently become possible with LIGO/Virgo observations of black hole mergers. However, one obstacle to extracting the most stringent constraints possible is the lack of predictions of what black hole coalescence should ""sound"" like in modified gravity theories, or theories that offer exotic alternatives to black holes. To make things worse, many proposed alternatives do not have sufficiently well developed theoretical underpinnings to make concrete waveform predictions, or if they do, often have underlying equations that seem classically ill-posed. Here I will describe numerical approaches to attempt to ascertain the viability of two beyond-GR constructions : gravitational collapse in Einstein-dilaton-Gauss-Bonnet gravity, and the dynamical stability of AdS black bubbles.
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