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¯>1−2Λ¯4+Λ¯/3, the black-hole spacetimes are characterized by slowly decaying resonant modes which are described by the compact formula ℑω(n)=κ+⋅(n+12) [here the physical parameters {a¯,κ+,Λ¯,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.