Speaker
Description
Understanding gauge and frame dependence is crucial for comparing black hole perturbation theory results at future null infinity. At second order, new challenges arise: gauge-invariant quantities in linear theory lose their invariance, and the nonlinear source terms can lead to infrared divergences. We address these issues by constructing an invariant second-order field equation in the perturbative Bondi–Sachs gauge, which naturally describes gravitational waves at null infinity. Our framework provides a systematic way to transform from any gauge to Bondi–Sachs and fix the BMS frame (the symmetry group of future null infinity and the Bondi--Sachs gauge). Our formalism could resolve tensions between second-order self-force and post-Newtonian results and help align ringdown calculations with numerical relativity waveforms.
