English

Non-closed subgroups of weakly branch groups

Group Theory 2025-11-20 v1

Abstract

For a weakly branch group GG acting on a regular enough rooted tree, we provide two constructions of continuous families of distinct subgroups that are not closed in the profinite topology on GG. On the one hand, we construct a continuous family of distinct non-closed subgroups such that each HH in the family is not ERF, that is, contains subgroups not closed in the profinite topology on HH. On the other hand, under an additional assumption on GG, we construct a continuous family of ERF subgroups which are not closed in the congruence (and in the profinite) topology on GG.

Keywords

Cite

@article{arxiv.2511.15277,
  title  = {Non-closed subgroups of weakly branch groups},
  author = {Jorge Fariña-Asategui and Paul-Henry Leemann and Tatiana Nagnibeda},
  journal= {arXiv preprint arXiv:2511.15277},
  year   = {2025}
}

Comments

11 pages

R2 v1 2026-07-01T07:44:59.166Z