Geometric invariants for a class of submodules of analytic Hilbert modules via the sheaf model

TL;DR

This paper develops geometric invariants for submodules of analytic Hilbert modules using sheaf theory, focusing on the structure of associated coherent sheaves and their zero sets, to classify submodules via vector bundle invariants.

Contribution

It introduces a hermitian structure for coherent sheaves associated to submodules and establishes invariants based on the kernel decomposition along zero sets.

Findings

Existence of a unique local kernel decomposition along zero sets.

Construction of a holomorphic frame for a vector bundle on the zero set.

Complex geometric invariants serve as unitary invariants for submodules.

Abstract

Let $\Omega \subseteq \mathbb C^m$ be a bounded connected open set and $\mathcal H \subseteq \mathcal O(\Omega)$ be an analytic Hilbert module, i.e., the Hilbert space $\mathcal H$ possesses a reproducing kernel $K$, the polynomial ring $\mathbb C[\boldsymbol{z}]\subseteq \mathcal H$ is dense and the point-wise multiplication induced by $p\in \mathbb C[\boldsymbol{z}]$ is bounded on $\mathcal H$. We fix an ideal $\mathcal I \subseteq \mathbb C[\boldsymbol{z}]$ generated by $p_1,\ldots,p_t$ and let $[\mathcal I]$ denote the completion of $\mathcal I$ in $\mathcal H$. The sheaf $\mathcal S^\mathcal H$ associated to analytic Hilbert module $\mathcal H$ is the sheaf $\mathcal O(\Omega)$ of holomorphic functions on $\Omega$ and hence is free. However, the subsheaf $\mathcal S^{\mathcal [\mathcal I]}$ associated to $[\mathcal I]$ is coherent and not necessarily locally free. Building on the earlier work of \cite{BMP}, we prescribe a hermitian structure for a coherent sheaf and use it to find tractable invariants. Moreover, we prove that if the zero set $V_{[\mathcal I]}$ is a submanifold of codimension $t$, then there is a unique local decomposition for the kernel $K_{[\mathcal I]}$ along the zero set that serves as a holomorphic frame for a vector bundle on $V_{[\mathcal I]}$. The complex geometric invariants of this vector bundle are also unitary invariants for the submodule $[\mathcal I] \subseteq \mathcal H$.