Quasisymmetric maps of boundaries of amenable hyperbolic groups

Abstract

In this paper we show that if $Y=N\times {\mathbb{Q}}_m$ is a metric space where $N$ is a Carnot group endowed with the Carnot-Caratheodory metric then any quasisymmetric map of $Y$ is actually bilipschitz. The key observation is that $Y$ is the parabolic visual boundary of a mixed type locally compact amenable hyperbolic group. The same results also hold for a larger class of nilpotent Lie groups $N$. As part of the proof we also obtain partial quasi-isometric rigidity results for mixed type locally compact amenable hyperbolic groups. Finally we prove a rigidity result for uniform subgroups of bilipschitz maps of $Y$ in the case of $N={\mathbb{R}}^n$.

To appear in the Indiana University Mathematics Journal, 19 pages