Noncommutative Joinings II

Abstract: This paper is a continuation of the authors' previous work on noncommutative joinings, and contains a study of relative independence of W$^*$-dynamical systems. We prove that, given any separable locally compact group $G$, an ergodic W$^{*}$-dynamical $G$-system $\mathfrak{M}$ with compact subsystem $\mathfrak{N}$ is disjoint relative to $\mathfrak{N}$ from its maximal compact subsystem $\mathfrak{M}{K}$ if and only if $\mathfrak{N}\cong\mathfrak{M}{K}$. This generalizes recent work of Duvenhage, which established the result for $G$ abelian.