Non-Commutative Wiener-Wintner theorem for amenable group actions

Abstract

Let $G$ be a locally compact second countable amenable group acting on a finite von Neumann algebra $(\mathcal{M},τ)$ by trace-preserving automorphisms. In this article, we establish a Jacobs-de Leeuw-Glicksberg decomposition for this action, obtaining a decomposition of $\mathcal{M}$ into its almost periodic and weakly mixing components. As an application, we prove a noncommutative Wiener--Wintner theorem for amenable group actions on finite von Neumann algebras.