The almost simple fixer-ratio conjecture

Let GG be an almost simple primitive permutation group, meaning that G0\trianglelefteqslantGAut(G0)G_0\trianglelefteqslant G\leqslant\operatorname{Aut}(G_0) for a non-abelian simple group G0G_0, with G0=soc(G)G_0=\operatorname{soc}(G). Let ρ0(G)\rho_0(G) be the fixer-ratio invariant defined by

ρ0(G):=max{KHΩ:KG is a fixer}.\rho_0(G):=\max\left\{\frac{|K|}{|H|\sqrt{|\Omega|}}:K\leqslant G\text{ is a fixer}\right\}.

Almost simple fixer-ratio conjecture. We have

ρ0(G)1\rho_0(G)\leqslant 1

for all almost simple primitive groups GG. This is presented in the source as an equivalent formulation of the bounded fixer-ratio conjecture for primitive groups, via suitable product actions. Its status is open in the supplied source.

Sources & referencesView supporting material

Primary source

Hong Yi Huang, Cai Heng Li and Yi Lin Xie, “Fixers and derangements of finite permutation groups”, arXiv:2404.18753 (2025).

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