Spectral instabilities in the time domain
Abstract
We investigate the effect of a spectral instability on the time domain waveform using a one-dimensional double Pöschl-Teller model. By analytically following successive scatterings between the primary potential barrier and a weak, spatially separated perturbation, we identify a secular contribution that first appears after one causal round trip between the barriers. Before the first echo, all overtones remain at their unperturbed frequencies. After the first echo reaches the observer, there is a secular, linear-in-time correction. When this correction is perturbative, it can be interpreted as a shift of the quasinormal mode frequency. In that case, we show that its coefficient reproduces the frequency-domain result. More generally, it generates finite-time effective frequencies that need not coincide with either the unperturbed or fully perturbed quasi-normal mode spectrum. We confirm the results of our analytic calculation using numerical time-domain evolutions.
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BibTeX
@misc{may2026spectral,
title = {{Spectral instabilities in the time domain}},
author = {Taillte May and Adrien Kuntz and Nicola Franchini and Valentin Boyanov and Vitor Cardoso},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.35993},
eprint = {2609.35993},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.35993},
}
RIS
TY - UNPB
TI - Spectral instabilities in the time domain
AU - Taillte May
AU - Adrien Kuntz
AU - Nicola Franchini
AU - Valentin Boyanov
AU - Vitor Cardoso
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.35993
UR - https://arxiv.org/abs/2609.35993
AB - We investigate the effect of a spectral instability on the time domain waveform using a one-dimensional double Pöschl-Teller model. By analytically following successive scatterings between the primary potential barrier and a weak, spatially separated perturbation, we identify a secular contribution that first appears after one causal round trip between the barriers. Before the first echo, all overtones remain at their unperturbed frequencies. After the first echo reaches the observer, there is a secular, linear-in-time correction. When this correction is perturbative, it can be interpreted as a shift of the quasinormal mode frequency. In that case, we show that its coefficient reproduces the frequency-domain result. More generally, it generates finite-time effective frequencies that need not coincide with either the unperturbed or fully perturbed quasi-normal mode spectrum. We confirm the results of our analytic calculation using numerical time-domain evolutions.
ER -