Nonoscillatory gravitational quasinormal modes of Reissner–Nordström–de Sitter spacetime
Phys. Rev. D 114, 084038 – Published 13 October, 2026
DOI: https://doi.org/10.1103/rmkq-fz1t
Abstract
We revisit quasinormal modes of Reissner–Nordström–de Sitter black holes, a classical and seemingly well-understood solution of Einstein-Maxwell theory with a positive cosmological constant. While previous studies have focused almost exclusively on the oscillatory photon-sphere branch, we show that two additional branches of non-oscillatory, purely imaginary modes—associated with the de Sitter horizon and with the regime of near-extremal charge (zero damped)—are essential for a complete description of the spectrum. These modes have so far remained largely unexplored for gravitational perturbations despite their relevance for late-time dynamics and stability. In particular, we derive accurate analytic expressions for the purely imaginary quasinormal frequencies in the slow-damping regime, providing a complete description of this sector of the spectrum.
