Quasinormal modes of Hayward black holes from Schwarzschild to extremality: a comparative spectral analysis

Abstract

We study scalar and electromagnetic quasinormal modes of the Hayward black hole and the axial spectrum of a specified Regge--Wheeler-type effective model, from the Schwarzschild limit to exact extremality. Multiprecision Chebyshev collocation reproduces most available low-lying oscillatory benchmarks and supplies further overtone candidates. The spin-2 equation is model dependent. It differs from the effective-source potential used in recent Hayward studies, and we quantify representative frequency differences. The discretisation also produces purely imaginary eigenvalue sequences, whose physical classification requires special care because highly reproducible imaginary-axis ladders need not be poles of the continued Green function. Accordingly, the imaginary-axis entries reported here are retained as unclassified spectral candidates, not established QNMs. We quantify their finite-table gap dispersion and sensitivity to the number of included gaps. Their spacings near one quarter in $M\omega$, and the extremal product near $1/3$ with the throat radius, remain properties of the tabulated candidates, and they do not establish universal QNM spacing or throat-controlled damping.

29 pages

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