English

Weakly maximal subgroups in regular branch groups

Group Theory 2017-05-30 v3

Abstract

Let GG be a finitely generated regular branch group acting by automorphisms on a regular rooted tree TT. It is well-known that stabilizers of infinite rays in TT (aka parabolic subgroups) are weakly maximal subgroups in GG, that is, maximal among subgroups of infinite index. We show that, given a finite subgroup QGQ\leq G, GG possesses uncountably many automorphism equivalence classes of weakly maximal subgroups containing QQ. In particular, for Grigorchuk-Gupta-Sidki type groups this implies that they have uncountably many automorphism equivalence classes of weakly maximal subgroups that are not parabolic.

Keywords

Cite

@article{arxiv.1502.07283,
  title  = {Weakly maximal subgroups in regular branch groups},
  author = {Khalid Bou-Rabee and Paul-Henry Leemann and Tatiana Nagnibeda},
  journal= {arXiv preprint arXiv:1502.07283},
  year   = {2017}
}

Comments

11 pages; a few corrections; to appear in J. Algebra

R2 v1 2026-06-22T08:38:01.327Z