English

The Saxl hypergraph of a permutation group

Group Theory 2025-05-21 v1 Combinatorics

Abstract

Given a permutation group GSym(Ω)G \le \mathrm{Sym}(\Omega), a subset BB of Ω\Omega is said to be a base if its pointwise stabiliser in GG is trivial, and the base size b(G)b(G) is the minimum size of a base. In the notable case b(G)=2b(G) = 2, Burness and Giudici define the Saxl graph of GG to be the graph on Ω\Omega with bases of size 2 as edges. Later work of Freedman et al. extends this notion to any group for which b(G)2b(G) \ge 2, taking the pairs of points contained in bases of size b(G)b(G) for edges. We study an alternative generalisation, the Saxl hypergraph, where bases of size b(G)b(G) are themselves the edges. In particular, we consider groups with complete Saxl hypergraphs, primitive groups whose Saxl hypergraphs have flag-spanning tours, and appropriate generalisations of Burness and Giudici's Common Neighbour Conjecture.

Keywords

Cite

@article{arxiv.2505.13849,
  title  = {The Saxl hypergraph of a permutation group},
  author = {Melissa Lee and Anthony Pisani},
  journal= {arXiv preprint arXiv:2505.13849},
  year   = {2025}
}

Comments

31 pages

R2 v1 2026-07-01T02:23:47.400Z