$\mathfrak{K}$-families and CPD-H-extendable families

Abstract

We introduce, for any set $S$, the concept of $\mathfrak{K}$-family between two Hilbert $C^{\ast }$-modules over two $C^{\ast }$-algebras, for a given completely positive definite (CPD-) kernel $\mathfrak{K}$ over $S$ between those $C^{\ast }$-algebras and obtain a factorization theorem for such $\mathfrak{K}$-families. If $\mathfrak{K}$ is a CPD-kernel and $E$ is a full Hilbert $C^{\ast }$-module, then any $\mathfrak{K}$-family which is covariant with respect to a dynamical system $(G,\eta ,E)$ on $E$, extends to a $\tilde{\mathfrak{K}}$-family on the crossed product $E{\times }_{\eta }G$, where $\tilde{\mathfrak{K}}$ is a CPD-kernel. Several characterizations of $\mathfrak{K}$-families, under the assumption that $E$ is full, are obtained and covariant versions of these results are also given. One of these characterizations says that such $\mathfrak{K}$-families extend as CPD-kernels, between associated (extended) linking algebras, whose $(2,2)$-corner is a homomorphism and vice versa. We discuss a dilation theory of CPD-kernels in relation to $\mathfrak{K}$-families.

22 pages, 6 figures

Cited by in corpus (2)

• Bures distance and transition probability for $\alpha$-CPD-kernels
• Block quantum dynamical semigroups of completely positive definite kernels