Dirichlet–Voronoi domain and injectivity radius of flag manifolds — equivariant cell structure on O(3)∕O(1)3

Garnier, Arthur

doi:10.2140/agt.2026.26.2181

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Dirichlet–Voronoi domain and injectivity radius of flag manifolds — equivariant cell structure on $O(3)/O(1)^3$

Arthur Garnier

Algebraic & Geometric Topology 26 (2026) 2181–2214

DOI: 10.2140/agt.2026.26.2181

Abstract

In the first part of this work, we study Dirichlet–Voronoi domains for discrete isometry groups of Riemannian manifolds, in view of constructing cell structures on homogeneous (complete, real) flag manifolds, equivariant with respect to the action of the Weyl group. We give general results, allowing us to build such a structure from an admissible one on the domain. In particular, the injectivity radius plays a key role in the method.

The second part starts with the computation of the injectivity radius of (real and complex) flag manifolds; a first step towards the application of the method developed in the first part. Then, with the help of the quaternion algebra, we investigate the particular case of the flag manifold $O (3) ∕ O {(1)}^{3}$ of ${SL}_{3} (ℝ)$ : we prove that the results of the first part apply and derive a new $𝔖_{3}$ -equivariant cell structure on it, whose cellular complex of $ℤ [𝔖_{3}]$ -modules is determined.

Keywords

flag manifold, Weyl group, equivariant CW structure, Dirichlet domain, equivariant algebraic topology

Mathematical Subject Classification

Primary: 14M15, 57M60, 57R91

Secondary: 22E99, 53C21

References

Publication

Received: 25 June 2024

Revised: 26 February 2025

Accepted: 29 May 2025

Published: 22 June 2026

Authors

Arthur Garnier
LAMFA Université de Picardie Jules Verne, CNRS UMR 7352 Amiens France

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Volume 26, issue 6 (2026)