Tensorial Function Theory: From Berezin transforms to Taylor's Taylor series and back

Abstract

Let $H^{\infty}(E)$ be the Hardy algebra of a $W^{*}$-correspondence $E$ over a $W^{*}$-algebra $M$. Then the ultraweakly continuous completely contractive representations of $H^{\infty}(E)$ are parametrized by certain sets $\mathcal{AC}(\sigma)$ indexed by $NRep(M)$ - the normal *-representations $\sigma$ of $M$. Each set $\mathcal{AC}(\sigma)$ has analytic structure, and each element $F\in H^{\infty}(E)$ gives rise to an analytic operator-valued function $\hat{F}_{\sigma}$ on $\mathcal{AC}(\sigma)$ that we call the $\sigma$-Berezin transform of $F$. The sets ${\mathcal{AC}(\sigma)}_{\sigma\in\Sigma}$ and the family of functions ${\hat{F}_{\sigma}}_{\sigma\in\Sigma}$ exhibit "matricial structure" that was introduced by Joeseph Taylor in his work on noncommutative spectral theory in the early 1970s. Such structure has been exploited more recently in other areas of free analysis and in the theory of linear matrix inequalities. Our objective here is to determine the extent to which the matricial structure characterizes the Berezin transforms.