Eikonal quasinormal modes of highly-spinning black holes in higher-curvature gravity: a window into extremality

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Main Authors: Cano, Pablo A., David, Marina, van der Velde, Guido
Format: Preprint
Published: 2025
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author Cano, Pablo A.
David, Marina
van der Velde, Guido
author_facet Cano, Pablo A.
David, Marina
van der Velde, Guido
contents We carry out the first computation of gravitational quasinormal modes of black holes with arbitrary rotation in a theory with higher-derivative corrections. Our analysis focuses on a recently identified quartic-curvature theory that preserves the isospectrality of quasinormal modes in the eikonal limit and that is connected to string theory. We find a master equation that governs large-momentum gravitational perturbations in this theory. By solving this equation with WKB methods, we provide complete results for the corrections to the Kerr quasinormal mode frequencies for arbitrary spin and arbitrary $μ=m/(\ell+1/2)$, where $\ell$ and $m$ are the harmonic numbers. Our results show that the corrections become orders of magnitude larger when the spin is close to extremality, with the modes close to the critical value of $μ$ that separates damped and zero-damped modes being particularly sensitive. We also perform a geometric-optics analysis of gravitational-wave propagation around black holes and relate the equatorial ``graviton-sphere'' orbits to quasinormal mode frequencies with $\ell=m$. We find that the usual correspondence between the Lyapunov exponent of those orbits and the imaginary part of the frequency is modified.
format Preprint
id arxiv_https___arxiv_org_abs_2509_08664
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Eikonal quasinormal modes of highly-spinning black holes in higher-curvature gravity: a window into extremality
Cano, Pablo A.
David, Marina
van der Velde, Guido
General Relativity and Quantum Cosmology
High Energy Physics - Theory
We carry out the first computation of gravitational quasinormal modes of black holes with arbitrary rotation in a theory with higher-derivative corrections. Our analysis focuses on a recently identified quartic-curvature theory that preserves the isospectrality of quasinormal modes in the eikonal limit and that is connected to string theory. We find a master equation that governs large-momentum gravitational perturbations in this theory. By solving this equation with WKB methods, we provide complete results for the corrections to the Kerr quasinormal mode frequencies for arbitrary spin and arbitrary $μ=m/(\ell+1/2)$, where $\ell$ and $m$ are the harmonic numbers. Our results show that the corrections become orders of magnitude larger when the spin is close to extremality, with the modes close to the critical value of $μ$ that separates damped and zero-damped modes being particularly sensitive. We also perform a geometric-optics analysis of gravitational-wave propagation around black holes and relate the equatorial ``graviton-sphere'' orbits to quasinormal mode frequencies with $\ell=m$. We find that the usual correspondence between the Lyapunov exponent of those orbits and the imaginary part of the frequency is modified.
title Eikonal quasinormal modes of highly-spinning black holes in higher-curvature gravity: a window into extremality
topic General Relativity and Quantum Cosmology
High Energy Physics - Theory
url https://arxiv.org/abs/2509.08664