Gravitational shockwaves on rotating black holes

Abstract

We present an exact solution of Einstein's equation that describes the gravitational shockwave of a massless particle on the horizon of a Kerr-Newman black hole. The backreacted metric is of the generalized Kerr-Schild form and is Type II in the Petrov classification. We show that if the background frame is aligned with shear-free null geodesics, and if the background Ricci tensor satisfies a simple condition, then all nonlinearities in the perturbation will drop out of the curvature scalars. We make heavy use of the method of spin coefficients (the Newman-Penrose formalism) in its compacted form (the Geroch-Held-Penrose formalism).

v4: Substantially shortened (45 pages). Major casualties: Point-particle limit of field theory and over 100 footnotes. Minor casualties: Detailed exposition of background material. Corrections: Formal redefinition of Ricci and energy scalars from traceless tensors, note about extrinsic curvature, a stray prime, some numerical factors. No results were harmed. v5: Minor edits. v6: Published