JournalsggdVol. 4 , No. 1DOI 10.4171/ggd/72

Geometric characterization of flat groups of automorphisms

  • Udo Baumgartner

    University of Wollongong, Australia
  • Günter Schlichting

    TU München, Garching, Germany
  • George A. Willis

    The University of Newcastle, Callaghan, Australia
Geometric characterization of flat groups of automorphisms cover

Abstract

If ℋ is a flat group of automorphisms of finite rank n of a totally disconnected, locally compact group G, then each orbit of ℋ in the metric space ℬ(G) of compact, open subgroups of G is quasi-isometric to n-dimensional Euclidean space. In this note we prove the following partial converse: Assume that G is a totally disconnected, locally compact group such that ℬ(G) is a proper metric space and let ℋ be a group of automorphisms of G such that some (equivalently every) orbit of ℋ in ℬ(G) is quasi-isometric to n-dimensional Euclidean space, then ℋ has a finite index subgroup which is flat of rank n. We can draw this conclusion under weaker assumptions. We also single out a naturally defined flat subgroup of such groups of automorphisms.