A transference principle for involution-invariant functional Hilbert spaces

TL;DR

This paper establishes a transference principle for involution-invariant Hilbert spaces, providing a unitary equivalence and explicit kernel formulas, with applications to several complex domains and von Neumann's inequality analogs.

Contribution

It introduces a new transference scheme for involution-invariant Hilbert spaces, linking them via explicit kernels and unitary maps, applicable to various complex domains.

Findings

Unitary equivalence between certain Hilbert spaces and involution-invariant subspaces.

Explicit formula for the reproducing kernel in the transferred space.

Application to domains like symmetrized bidisc and tetrablock, enabling von Neumann inequality analogs.

Abstract

Let $\sigma : \mathbb C^d \rightarrow \mathbb C^d$ be an affine-linear involution such that $J_\sigma = -1$ and let $U, V$ be two domains in $\mathbb C^d.$ Let $\phi : U \rightarrow V$ be a $\sigma$-invariant $2$-proper map such that $J_\phi$ is affine-linear and let $\mathscr H(U)$ be a $\sigma$-invariant reproducing kernel Hilbert space of complex-valued holomorphic functions on $U.$ It is shown that the space $\mathscr H_\phi(V):=\{f \in \mathrm{Hol}(V) : J_\phi \cdot f \circ \phi \in \mathscr H(U)\}$ endowed with the norm $\|f\|_\phi :=\|J_\phi \cdot f \circ \phi\|_{\mathscr H(U)}$ is a reproducing kernel Hilbert space and the linear mapping $\varGamma_\phi$ defined by $ \varGamma_\phi(f) = J_\phi \cdot f \circ \phi,$ $f \in \mathrm{Hol}(V),$ is a unitary from $\mathscr H_\phi(V)$ onto $\{f \in \mathscr H(U) : f = -f \circ \sigma\}.$ Moreover, a neat formula for the reproducing kernel $\kappa_{\phi}$ of $\mathscr H_\phi(V)$ in terms of the reproducing kernel of $\mathscr H(U)$ is given. The above scheme is applicable to symmetrized bidisc, tetrablock, $d$-dimensional fat Hartogs triangle and $d$-dimensional egg domain. Although some of these are known, this allows us to obtain an analog of von Neumann's inequality for contractive tuples naturally associated with these domains.