Extensions of automorphisms of self-similar groups

Francesco Matucci, Pedro V. Silva

Published 2018-06-25Version 1

In this work we study automorphisms of synchronous self-similar groups, the existence of extensions to automorphisms of the full group of automorphisms of the infinite rooted tree on which these groups act on. When they do exist, we obtain conditions for the continuity of such extensions with respect to the depth metric, but we also construct examples of groups where such extensions do not exist. We study the case of the lamplighter group $\mathcal{L}_k = \mathbb{Z}_k \wr \mathbb{Z}$ and show that all of its automorphisms admit a continuous extension and determine necessary and sufficient conditions for when the automorphism group of $\mathcal{L}_k$ is finitely generated.