Quasi-normal modes of non-separable perturbation equations: the scalar non-Kerr case

, NOBLEBLOCKS; Ghosh, Rajes; H. Völkel, Sebastian; Franchini, Nicola; Barausse, Enrico

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Quasi-normal modes of non-separable perturbation equations: the scalar non-Kerr case

Shared by Jamie Larson on Nov 15, 2025 • 04:54 AM UTC

Authors:

Rajes Ghosh

Sebastian H. Völkel

Nicola Franchini

Abstract

Scalar, vector and tensor perturbations on the Kerr spacetime are governed by equations that can be solved by separation of variables, but the same is not true in generic stationary and axisymmetric geometries. This complicates the calculation of black-hole quasi-normal mode frequencies in theories ...

Subject

quasinormal modes

Kerr black holes

non-Kerr spacetimes

Highlights

-Introduces a perturbative method to compute BH QNM frequencies for backgrounds close to Kerr with non-separable perturbations.

-Reduces the problem to an ordinary differential equation for the radial function at leading order in the deviation from Kerr.

-Demonstrates the method on scalar perturbations for slowly rotating Kerr and Schwarzschild with an anomalous quadrupole moment, showing small deviations from Kerr results and validating with multiple checks.

-Explores the eikonal limit and confirms the correspondence between QNMs and photon ring properties in the perturbed spacetimes.

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