IR extremality and UV softness in string bootstrap
Abstract
Whether string amplitudes can be characterized by extremality within the space of consistent S-matrices is an intriguing question. We address this question within the framework of positivity bootstrap. We compute positivity bounds by minimizing the F4 Wilson coefficient while fixing subleading coefficients, and show that the Veneziano amplitude lies close to the boundary of the allowed region. However, this numerical proximity does not imply exact extremality, as demonstrated by explicit counterexamples. When additional KLT-motivated UV softness is imposed, the Veneziano amplitude is found to uniquely minimize the F4 coefficient for 4≤ D≤10, connecting the extremality of the Veneziano amplitude to its stringy UV behavior and offering a new perspective on what makes string theory special.
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BibTeX
@misc{wan2026extremality,
title = {{IR extremality and UV softness in string bootstrap}},
author = {Shi-Lin Wan and Ji-Yang Wang and Shuang-Yong Zhou},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27084},
eprint = {2610.27084},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27084},
}
RIS
TY - UNPB
TI - IR extremality and UV softness in string bootstrap
AU - Shi-Lin Wan
AU - Ji-Yang Wang
AU - Shuang-Yong Zhou
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.27084
UR - https://arxiv.org/abs/2610.27084
AB - Whether string amplitudes can be characterized by extremality within the space of consistent S-matrices is an intriguing question. We address this question within the framework of positivity bootstrap. We compute positivity bounds by minimizing the F^4 Wilson coefficient while fixing subleading coefficients, and show that the Veneziano amplitude lies close to the boundary of the allowed region. However, this numerical proximity does not imply exact extremality, as demonstrated by explicit counterexamples. When additional KLT-motivated UV softness is imposed, the Veneziano amplitude is found to uniquely minimize the F^4 coefficient for 4≤ D≤10, connecting the extremality of the Veneziano amplitude to its stringy UV behavior and offering a new perspective on what makes string theory special.
ER -