English

Almost-automorphisms of trees, cloning systems and finiteness properties

Group Theory 2021-04-15 v2

Abstract

We prove that the group of almost-automorphisms of the infinite rooted regular dd-ary tree Td\mathcal{T}_d arises naturally as the Thompson-like group of a so called dd-ary cloning system. A similar phenomenon occurs for any R\"over-Nekrashevych group Vd(G)V_d(G), for GAut(Td)G\le Aut(\mathcal{T}_d) a self-similar group. We use this framework to expand on work of Belk and Matucci, who proved that the R\"over group, using the Grigorchuk group for GG, is of type FF_\infty. Namely, we find some natural conditions on subgroups of GG to ensure that Vd(G)V_d(G) is of type FF_\infty, and in particular we prove this for all GG in the infinite family of \v{S}uni\'c groups. We also prove that if GG is itself of type FF_\infty then so is Vd(G)V_d(G), and that every finitely generated virtually free group is self-similar, so in particular every finitely generated virtually free group GG yields a type FF_\infty R\"over-Nekrashevych group Vd(G)V_d(G).

Keywords

Cite

@article{arxiv.1709.06524,
  title  = {Almost-automorphisms of trees, cloning systems and finiteness properties},
  author = {Rachel Skipper and Matthew C. B. Zaremsky},
  journal= {arXiv preprint arXiv:1709.06524},
  year   = {2021}
}

Comments

44 pages, 11 figures. v2: accepted version, published in J. Topol. Anal