title: Gravitoelectromagnetic perturbations of Kerr-Newman black holes: stability and isospectrality in the slow-rotation limit.
abstract: The most general stationary black-hole solution of Einstein-Maxwell theory in vacuum is the Kerr-Newman metric, specified by three parameters: mass M, spin J, and charge Q. Within classical general relativity, one of the most important and challenging open problems in black-hole perturbation theory is the study of gravitational and electromagnetic fields in the Kerr-Newman geometry, because of the indissoluble coupling of the perturbation functions. Here we circumvent this long-standing problem by working in the slow-rotation limit. We compute the quasinormal modes up to linear order in J for any value of Q and provide the first, fully consistent stability analysis of the Kerr-Newman metric. For scalar perturbations the quasinormal modes can be computed exactly, and we demonstrate that the method is accurate within 3% for spins J/J(max) ≲ 0.5, where J(max) is the maximum allowed spin for any value of Q. Quite remarkably, we find numerical evidence that the axial and polar sectors of the gravitoelectromagnetic perturbations are isospectral to linear order in the spin. The extension of our results to nonasymptotically flat space-times could be useful in the context of gauge-gravity dualities and string theory.
authors.affiliation: CENTRA, Departamento de Física, Instituto Superior Técnico, Universidade Técnica de Lisboa-UTL, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal and Institute for Theory and Computation, Harvard-Smithsonian CfA, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Paolo
authors.initials: P
authors.lastname: Pani
authors.affiliation: Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677, USA and California Institute of Technology, Pasadena, Californai 91109, USA.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Berti
authors.affiliation: Dipartimento di Fisica, Università di Roma "La Sapienza" & Sezione INFN Roma1, P.A. Moro 5, 00185 Roma, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Gualtieri