On dualities of actions

Abstract

We introduce the notion of the weak tracial approximate representability of a discrete group action on a unital $C^*$-algebra which could have no projections like the Jiang-Su algebra $\mathcal{Z}$. Then we show a duality between the weak tracial Rokhlin property and the weak tracial approximate representability. More precisely, when $G$ is a finite abelian group and $\alpha:G\curvearrowright A$ is a group action on a unital simple infinite dimensional $C^*$-algebra, we prove that 1. $\alpha$ has the weak tracial Rokhlin property if and only if $\hat{\alpha}$ has the weak tracial approximate representability. 2. $\alpha$ has the weak tracial approximate representability if and only if $\hat{\alpha}$ has the weak tracial Rokhlin property.