Totally disconnected locally compact groups with just infinite locally normal subgroups

Abstract

We obtain a characterization of totally disconnected, locally compact groups $G$ with the following property: given a locally normal subgroup $K$ of $G$, then there is an open subgroup of $K$ that is a direct factor of an open subgroup of $G$. This property is motivated by J. Wilson's structure theory of just infinite groups, and indeed, when $G$ has trivial quasi-centre, the condition turns out to be equivalent to the condition that $G$ is locally isomorphic to a finite direct product of just infinite profinite groups. In the latter situation we obtain some global structural features of $G$, building on an earlier result of Barnea--Ershov--Weigel and also using tools developed by P.-E. Caprace, G. Willis and the author for studying local structure in totally disconnected locally compact groups.