On simplicity of intermediate C*-algebras

Abstract: We prove simplicity of all intermediate $C^*$-algebras $C^*_{r}(\Gamma)\subseteq \mathcal{B} \subseteq \Gamma\ltimes_r C(X)$ in the case of minimal actions of $C^*$-simple groups $\Gamma$ on compact spaces $X$. For this, we use the notion of stationary states, recently introduced by Hartman and Kalantar (arXiv:1712.10133v2). We show that the Powers' averaging property holds for the reduced crossed product $\Gamma\ltimes_r \mathcal{A}$ for any action $\Gamma\curvearrowright \mathcal{A}$ of a $C^*$-simple group $\Gamma$ on a unital $C^*$-algebra $\mathcal{A}$, and use it to prove a one-to-one correspondence between stationary states on $\mathcal{A}$ and those on $\Gamma\ltimes_r \mathcal{A}$.