The amenability constant of the Fourier algebra

Volker Runde

Published 2004-09-23, updated 2005-01-06Version 3

For a locally compact group $G$, let $A(G)$ denote its Fourier algebra and $\hat{G}$ its dual object, i.e. the collection of equivalence classes of unitary represenations of $G$. We show that the amenability constant of $A(G)$ is less than or equal to $\sup \{\deg(\pi) : \pi \in \hat{G} \}$ and that it is equal to one if and only if $G$ is abelian.