Quasinormal modes and strong cosmic censorship in near-extremal Kerr-Newman-de Sitter black-hole spacetimes

The quasinormal resonant modes of massless neutral fields in near-extremal Kerr-Newman-de Sitter black-hole spacetimes are calculated in the eikonal regime. It is explicitly proved that, in the angular momentum regime (a)over-bar > root 1-2(Lambda)over-bar/4+(Lambda)over-bar/3' the black-hole spacetimes are characterized by slowly decaying resonant modes which are described by the compact formula I omega(n) = kappa(+) . (n + 1/2) [here the physical parameters {(a)over-bar, kappa(+), (Lambda)over-bar, n} are respectively the dimensionless angular momentum of the black hole, its characteristic surface gravity, the dimensionless cosmological constant of the spacetime, and the integer resonance parameter]. Our results support the validity of the Penrose strong cosmic censorship conjecture in these black-hole spacetimes. (C) 2018 The Author. Published by Elsevier B.V.