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PreprintarXiv licencearXiv

Exact Cancellation of Horizon Modes in Kerr Ringdown

  • Kei-ichiro Kubota
  • Yusuke Manita
  • Hayato Motohashi
  • Daiki Watarai
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Abstract

Ringdown gravitational waves probe black hole spacetimes via quasinormal modes (QNMs). Recent studies have reported oscillatory features in QNM-filtered waveforms, and have led to conflicting interpretations as to whether they represent a near-horizon "direct wave". Reexamining a particle plunging into a Kerr black hole, we show that the saddle-point approximation underlying the proposed interpretation fails near the horizon. Our exact analysis reveals that every source-induced horizon-mode pole is canceled by an infinite tower of Matsubara zeros, independently of orbital and black-hole parameters. The first four stages of this sequential screening are also confirmed by time-domain numerical integration. Thus, within the near-horizon perturbative framework, source-induced horizon-mode signals do not survive at late times.

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Cite

BibTeXRIS
BibTeX
@misc{kubota2026exact,
  title = {{Exact Cancellation of Horizon Modes in Kerr Ringdown}},
  author = {Kei-ichiro Kubota and Yusuke Manita and Hayato Motohashi and Daiki Watarai},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.07326},
  eprint = {2609.07326},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.07326},
}
RIS
TY  - UNPB
TI  - Exact Cancellation of Horizon Modes in Kerr Ringdown
AU  - Kei-ichiro Kubota
AU  - Yusuke Manita
AU  - Hayato Motohashi
AU  - Daiki Watarai
PY  - 2026
DA  - 2026/09/07
PB  - arXiv
DO  - 10.48550/arxiv.2609.07326
UR  - https://arxiv.org/abs/2609.07326
AB  - Ringdown gravitational waves probe black hole spacetimes via quasinormal modes (QNMs). Recent studies have reported oscillatory features in QNM-filtered waveforms, and have led to conflicting interpretations as to whether they represent a near-horizon "direct wave". Reexamining a particle plunging into a Kerr black hole, we show that the saddle-point approximation underlying the proposed interpretation fails near the horizon. Our exact analysis reveals that every source-induced horizon-mode pole is canceled by an infinite tower of Matsubara zeros, independently of orbital and black-hole parameters. The first four stages of this sequential screening are also confirmed by time-domain numerical integration. Thus, within the near-horizon perturbative framework, source-induced horizon-mode signals do not survive at late times.
ER  -