Another Brick in the Wall: Spectral Form Factor of Normal Modes in Horizonless Geometries
Abstract
We compute the normal mode spectrum and its spectral form factor for a probe scalar wave in smooth horizonless backgrounds. We first consider the BTZ black hole with a brickwall that hides the near-horizon region, which has recently been proposed as a toy model for a finite-temperature semiclassical black hole microstate. In this setup, the spectral form factor may or may not have a linear ramp, depending on the details of the brickwall construction. However, we argue that even in cases that do show a ramp, this ramp does not originate from level correlations associated with quantum chaos. Then we calculate the normal mode spectrum for a genuine microstate geometry (superstratum) and find evidence of chaos, both with a ramp and level repulsion. We conclude that the eigenvalue spectrum of normal modes can indeed serve as a tool for investigating the quantum dynamics of fuzzballs; however, the brickwall models are incapable of capturing this phenomenon.
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BibTeX
@misc{belokon2026another,
title = {{Another Brick in the Wall: Spectral Form Factor of Normal Modes in Horizonless Geometries}},
author = {A. I. Belokon and M. Čubrović and V. Đukić and V. V. Pushkarev and L. Umrikhin},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37038},
eprint = {2610.37038},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37038},
}
RIS
TY - UNPB
TI - Another Brick in the Wall: Spectral Form Factor of Normal Modes in Horizonless Geometries
AU - A. I. Belokon
AU - M. Čubrović
AU - V. Đukić
AU - V. V. Pushkarev
AU - L. Umrikhin
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37038
UR - https://arxiv.org/abs/2610.37038
AB - We compute the normal mode spectrum and its spectral form factor for a probe scalar wave in smooth horizonless backgrounds. We first consider the BTZ black hole with a brickwall that hides the near-horizon region, which has recently been proposed as a toy model for a finite-temperature semiclassical black hole microstate. In this setup, the spectral form factor may or may not have a linear ramp, depending on the details of the brickwall construction. However, we argue that even in cases that do show a ramp, this ramp does not originate from level correlations associated with quantum chaos. Then we calculate the normal mode spectrum for a genuine microstate geometry (superstratum) and find evidence of chaos, both with a ramp and level repulsion. We conclude that the eigenvalue spectrum of normal modes can indeed serve as a tool for investigating the quantum dynamics of fuzzballs; however, the brickwall models are incapable of capturing this phenomenon.
ER -