Avoided crossings and resonances in black hole ringdown with coupled fields: A case study of the Einstein-Maxwell-axion system
Abstract
Avoided crossings in black hole quasinormal-mode (QNM) spectra exhibit characteristic resonant properties, including enhanced excitation factors. We extend the study of this phenomenon to perturbation systems with multiple coupled fields and investigate its consequences for ringdown waveforms. As a concrete example, we consider a charged black hole in the Einstein-Maxwell-axion system, whose QNM branches can be classified according to the gravitational, electromagnetic, and axion modes to which they continuously connect in the decoupling limit. We focus on an avoided crossing between the gravity- and electromagnetic-led branches thus defined. We verify that the QNM reconstruction accurately reproduces the ringdown portion of the directly evolved time-domain waveform. Near the avoided crossing, an effectively slower decay emerges for particular initial perturbations, while the resonantly enhanced contributions from the two QNMs largely cancel in the physical waveform. The QNM decomposition further reveals an exchange of the physical characters of the two branches across the resonance. These results characterize the imprint of resonances on black hole ringdown in systems with multiple coupled fields.
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BibTeX
@misc{takahashi2026avoided,
title = {{Avoided crossings and resonances in black hole ringdown with coupled fields: A case study of the Einstein-Maxwell-axion system}},
author = {Takuya Takahashi and Hayato Motohashi and Kazufumi Takahashi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.34401},
eprint = {2609.34401},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.34401},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Avoided crossings and resonances in black hole ringdown with coupled fields: A case study of the Einstein-Maxwell-axion system
AU - Takuya Takahashi
AU - Hayato Motohashi
AU - Kazufumi Takahashi
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.34401
UR - https://arxiv.org/abs/2609.34401
AB - Avoided crossings in black hole quasinormal-mode (QNM) spectra exhibit characteristic resonant properties, including enhanced excitation factors. We extend the study of this phenomenon to perturbation systems with multiple coupled fields and investigate its consequences for ringdown waveforms. As a concrete example, we consider a charged black hole in the Einstein-Maxwell-axion system, whose QNM branches can be classified according to the gravitational, electromagnetic, and axion modes to which they continuously connect in the decoupling limit. We focus on an avoided crossing between the gravity- and electromagnetic-led branches thus defined. We verify that the QNM reconstruction accurately reproduces the ringdown portion of the directly evolved time-domain waveform. Near the avoided crossing, an effectively slower decay emerges for particular initial perturbations, while the resonantly enhanced contributions from the two QNMs largely cancel in the physical waveform. The QNM decomposition further reveals an exchange of the physical characters of the two branches across the resonance. These results characterize the imprint of resonances on black hole ringdown in systems with multiple coupled fields.
ER -