Solubilizers in profinite groups

Abstract

The solubilizer of an element $x$ of a profinite group $G$ is the set of the elements $y$ of $G$ such that the subgroup of $G$ generated by $x$ and $y$ is prosoluble. We propose the following conjecture: the solubilizer of $x$ in $G$ has positive Haar measure if and only if $g$ centralizes "almost all" the non-abelian chief factors of $G$. We reduce the proof of this conjecture to another conjecture concerning finite almost simple groups: there exists a positive $c$ such that, for every finite simple group $S$ and every $(a,b)\in (Aut(S)\setminus \{1\}) \times Aut(S)$, the number of $s$ is $S$ such that $\langle a, bs\rangle $ is insoluble is at least $c|S|$. Work in progress by Fulman, Garzoni and Guralnick is leading to prove the conjecture when $S$ is a simple group of Lie type. In this paper we prove the conjecture for alternating groups.