Test for amenability for extensions of infinite residually finite groups

María Isabel Cortez, Jaime Gómez

Published 2024-01-10Version 1

Let $G$ be a countable group that admits a minimal equicontinuous action on the Cantor set (for example, a residually finite group). We show that the family of almost automorphic actions of $G$ on the Cantor set, is a test for amenability for $G$. More precisely, we show that if $G$ is non-amenable, then for every minimal equicontinuous system $(Y, G)$, such that $Y$ is a Cantor set, there exists a Toeplitz subshift with no invariant probability measures, whose maximal equicontinuous factor is $(Y,G)$. Consequently, we obtain that $G$ is amenable if and only if every Toeplitz $G$-subshift has at least one invariant probability measure.