Teukolsky master equation - de Rham wave equation for gravitational and electromagnetic fields in vacuum

A new version of the Teukolsky master equation, describing any massless field of spin s = 1/2, 1, 3/2 or 2 in a Kerr black hole, is presented here in the form of a wave equation containing additional curvature terms. These results suggest a relation between curvature perturbation theory in general relativity and the exact wave equations satisfied by the Weyl and the Maxwell tensors, known in the literature as the de Rham-Lichnerowicz Laplacian equations. We discuss these Laplacians both in terms of the Newman-Penrose formalism and the Geroch-Held-Penrose variant for an arbitrary vacuum spacetime. A perturbative expansion of these wave equations results in a recursive scheme valid for higher orders. This approach, apart from the obvious implications for gravitational and electromagnetic wave propagation in a curved spacetime, explains and extends the perturbative analysis results in the literature by clarifying their origins in the exact theory.