English

More on wreath products of cellular automata

Group Theory 2023-05-30 v1 Dynamical Systems

Abstract

We prove that if a subgroup HH of the automorphism group Aut(ΣZ)\mathrm{Aut}(\Sigma^{\mathbb{Z}}) of a non-trivial full shift acts on points of finite support with a free orbit, then for every finitely-generated abelian group AA, the abstract group AHA \wr H also embeds in Aut(ΣZ)\mathrm{Aut}(\Sigma^{\mathbb{Z}}). The groups admitting an action with such a free orbit include AZA \wr {\mathbb{Z}} for AA a finite abelian group, and finitely-generated free groups. The class of such groups is also closed under commensurability and direct products. We obtain for example that ZZ{\mathbb{Z}} \wr {\mathbb{Z}}, Z2(Z2Z){\mathbb{Z}}_2 \wr ({\mathbb{Z}}_2 \wr {\mathbb{Z}}) and Z(Z2Z){\mathbb{Z}} \wr ({\mathbb{Z}}_2 \wr {\mathbb{Z}}) embed in Aut(ΣZ)\mathrm{Aut}(\Sigma^{\mathbb{Z}}). To our knowledge, the group ZZ{\mathbb{Z}} \wr {\mathbb{Z}} is the first example of a finitely-generated torsion-free subgroup of Aut(ΣZ)\mathrm{Aut}(\Sigma^{\mathbb{Z}}) with infinite cohomological dimension. It answers an implicit question of Kim and Roush and an explicit question of the author. We also explore a simpler variant of the construction that gives some near-misses to iterated permutational wreath products, as well as some Neumann groups.

Keywords

Cite

@article{arxiv.2305.17946,
  title  = {More on wreath products of cellular automata},
  author = {Ville Salo},
  journal= {arXiv preprint arXiv:2305.17946},
  year   = {2023}
}

Comments

18 pages, 2 figures