English

A finitely generated branch group of exponential growth without free subgroups

Group Theory 2012-09-25 v2

Abstract

We will give an example of a branch group GG that has exponential growth but does not contain any non-abelian free subgroups. This answers question 16 from \cite{Bartholdi} positively. The proof demonstrates how to construct a non-trivial word wa,b(x,y)w_{a,b}(x,y) for any a,bGa,b \in G such that wa,b(a,b)=1w_{a,b}(a,b) = 1. The group GG is not just-infinite. We prove that every normal subgroup of GG is finitely generated as an abstract group and every proper quotient soluble. Further, GG has infinite virtual first Betti number but is not large.

Keywords

Cite

@article{arxiv.1207.6548,
  title  = {A finitely generated branch group of exponential growth without free subgroups},
  author = {Elisabeth Fink},
  journal= {arXiv preprint arXiv:1207.6548},
  year   = {2012}
}

Comments

16 pages, 1 figure