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

TL;DR

This paper explores the relationship between Berezin transforms and Taylor's matricial structure in the context of Hardy algebras over W*-correspondences, aiming to characterize Berezin transforms through this structure.

Contribution

It investigates how the matricial structure introduced by Taylor characterizes Berezin transforms within Hardy algebras of W*-correspondences.

Findings

Matricial structure helps in understanding Berezin transforms.

Analytic operator-valued functions are associated with algebra elements.

The study extends noncommutative spectral theory and free analysis.

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.