Black Strings and Black Holes: Worldsheet Spectra and Near-Extremal Limits
Abstract
We study aspects of the Euclidean partition function of the (SL(2,ℝ)× U(1))/U(1) gauged WZW model. The target space geometry is either a smooth horizonless geometry with a linear-dilaton asymptotic region, or the Horne--Horowitz black string, depending on which circles we unwind as the time-direction. We first study the worldsheet spectrum and obtain the character decomposition via the holonomy integrals. Next, we obtain the spacetime spectrum of the horizonless geometry by directly performing the unfolded modular integrals, and recover the Maldacena-Ooguri-Son spectrum in the ungauged limit. When the chirally charged three-dimensional black string is dimensionally reduced, the target space is instead a two-dimensional charged black hole. We study the near extremal regime of the black hole and black string. For the two dimensional black hole, we propose two candidate towers of states that produce the expected 3/2log T of the AdS2 throat from the worldsheet discrete series representation. These towers appear only below the temperature at which the full amplitude becomes divergent. We comment on the contribution of these states in the near-extremal limit of the full partition function.
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BibTeX
@misc{li2026black,
title = {{Black Strings and Black Holes: Worldsheet Spectra and Near-Extremal Limits}},
author = {Ziyi Li},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18591},
eprint = {2610.18591},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18591},
}
RIS
TY - UNPB
TI - Black Strings and Black Holes: Worldsheet Spectra and Near-Extremal Limits
AU - Ziyi Li
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18591
UR - https://arxiv.org/abs/2610.18591
AB - We study aspects of the Euclidean partition function of the (SL(2,ℝ)× U(1))/U(1) gauged WZW model. The target space geometry is either a smooth horizonless geometry with a linear-dilaton asymptotic region, or the Horne--Horowitz black string, depending on which circles we unwind as the time-direction. We first study the worldsheet spectrum and obtain the character decomposition via the holonomy integrals. Next, we obtain the spacetime spectrum of the horizonless geometry by directly performing the unfolded modular integrals, and recover the Maldacena-Ooguri-Son spectrum in the ungauged limit. When the chirally charged three-dimensional black string is dimensionally reduced, the target space is instead a two-dimensional charged black hole. We study the near extremal regime of the black hole and black string. For the two dimensional black hole, we propose two candidate towers of states that produce the expected 3/2log T of the AdS_2 throat from the worldsheet discrete series representation. These towers appear only below the temperature at which the full amplitude becomes divergent. We comment on the contribution of these states in the near-extremal limit of the full partition function.
ER -