Representing Locally Hilbert Spaces and Functional Models for Locally Normal Operators

TL;DR

This paper advances the spectral theory of locally normal operators by establishing a spectral theorem using projective limits of multiplication operators, and introduces a functional model based on inductive systems of measure spaces.

Contribution

It develops a new functional model for locally normal operators via inductive limits of $L^2$ spaces and proves a spectral theorem in terms of projective limits of multiplication operators.

Findings

Spectral theorem for locally normal operators established.

Functional model using inductive limits of $L^2$ spaces developed.

Connection with analysis on fractal sets suggested.

Abstract

The aim of this article is to explore in all remaining aspects the spectral theory of locally normal operators. In a previous article we proved the spectral theorem in terms of locally spectral measures. Here we prove the spectral theorem in terms of projective limits of certain multiplication operators with functions which are locally of type $L^\infty$. In order to do this, we first investigate strictly inductive systems of measure spaces and point out the concept of representing locally Hilbert space for which we obtain a functional model as a strictly inductive limit of $L^2$ type spaces. Then, we first obtain a functional model for locally normal operators on representing locally Hilbert spaces combined with a spectral multiplicity model on a pseudo-concrete functional model for the underlying locally Hilbert space, under a certain technical condition on the directed set. Finally, under the same technical condition on the directed set, we derive the spectral theorem for locally normal operators in terms of projective limits of certain multiplication operators with functions which are locally of type $L^\infty$ in two forms. As a consequence of the main result we sketch the direct integral representation of locally normal operators under the same technical assumptions and the separability of the locally Hilbert space. Examples of strictly inductive systems of measure spaces involving the Hata tree-like self-similar set, which justify the technical condition on a relevant case and which may open a connection with analysis on fractal sets, are included.