Finite presentability of twisted Brin-Thompson groups

Abstract

Given a group $G$ acting faithfully on a set $S$, we characterize precisely when the twisted Brin-Thompson group $S{V}_G$ is finitely presented. The answer is that $S{V}_G$ is finitely presented if and only if we have the following: $G$ is finitely presented, the action of $G$ on $S$ has finitely many orbits of two-element subsets of $S$, and the stabilizer in $G$ of any element of $S$ is finitely generated. Since twisted Brin-Thompson groups are simple, a consequence is that any subgroup of a group admitting an action as above satisfies the Boone-Higman conjecture. In the course of proving this, we also establish a sufficient condition for a group acting cocompactly on a simply connected complex to be finitely presented, even if certain edge stabilizers are not finitely generated, which may be of independent interest.

arXiv comment20 pages. V2: Accepted version, to appear in Proc. Roy. Soc. Edinburgh Sect. A