Profinite properties of Coxeter groups

Abstract

We prove a number of results about profinite completions of Coxeter groups. For example we prove Coxeter groups are good in the sense of Serre and that various splittings of Coxeter groups arising from actions on trees are detected by the profinite completion. As an application we prove a number of families of Coxeter groups are profinitely rigid amongst Coxeter groups. We also prove that Gromov-hyperbolic FC type, extra large type, and odd Coxeter groups are almost profinitely rigid amongst Coxeter groups. In the appendix, Sam Fisher and Sam Hughes show that the Atiyah Conjecture holds for all Coxeter groups, and that ${\ell }^2$-Betti numbers and their positive characteristic analogues are profinite invariants of Coxeter groups and of virtually compact special groups.

with an appendix by Sam P Fisher and Sam Hughes. v2: removed an erroneous proposition (results unaffected), changed font size, 45 pages. v1: 50 pages