A diameter gap for irreducible compact symmetric spaces of fixed rank
Abstract
We prove that, for every positive integer r, the positive normalized diameters of isometric quotients of simply connected irreducible compact Riemannian symmetric spaces of rank r have a uniform positive lower bound. The bound is independent of the dimension and of the acting group, which need not be connected. For the higher-dimensional Grassmannian families, we obtain an explicit bound for positive-dimensional acting groups by constructing nonconstant invariant functions of bounded trigonometric degree. The real and complex cases use moment maps. The quaternionic case follows from a quartic rigidity theorem proved by means of invariant four-forms and the classification of compact quaternionic symmetric spaces. We also give examples showing why the rank and the relative scales of product factors must be controlled.
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BibTeX
@misc{chen2026diameter,
title = {{A diameter gap for irreducible compact symmetric spaces of fixed rank}},
author = {Zhiqi Chen and Shaoqiang Deng and Hui Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.21535},
eprint = {2609.21535},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21535},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A diameter gap for irreducible compact symmetric spaces of fixed rank
AU - Zhiqi Chen
AU - Shaoqiang Deng
AU - Hui Zhang
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2609.21535
UR - https://arxiv.org/abs/2609.21535
AB - We prove that, for every positive integer r, the positive normalized diameters of isometric quotients of simply connected irreducible compact Riemannian symmetric spaces of rank r have a uniform positive lower bound. The bound is independent of the dimension and of the acting group, which need not be connected. For the higher-dimensional Grassmannian families, we obtain an explicit bound for positive-dimensional acting groups by constructing nonconstant invariant functions of bounded trigonometric degree. The real and complex cases use moment maps. The quaternionic case follows from a quartic rigidity theorem proved by means of invariant four-forms and the classification of compact quaternionic symmetric spaces. We also give examples showing why the rank and the relative scales of product factors must be controlled.
ER -