Determine quasinormal-mode and stability properties

Determine the quasinormal-mode spectrum and establish stability properties of the separated coupled gravitational and electromagnetic perturbations of subextremal Kerr–Newman–de Sitter black holes subject to the derived horizon conditions.

Background

The paper derives separated angular and radial systems and translates future black-hole and cosmological-horizon regularity into radial boundary conditions. These results provide the framework needed to formulate quasinormal-mode problems and investigate dynamical stability.

The actual spectral calculations and stability analysis are not carried out in the paper and are explicitly deferred to future work.