The class of n-entire operators

TL;DR

This paper classifies certain symmetric operators with deficiency indices (1,1) using geometric criteria, extending classical notions of entire operators and linking spectral properties to de Branges space theory.

Contribution

It introduces a new classification scheme for symmetric operators based on geometric criteria, expanding the theory of entire operators and their spectral analysis.

Findings

Operators classified by geometric criteria have distinctive spectral properties.

Necessary and sufficient spectral conditions for operator classification are established.

Connections to de Branges spaces are utilized to analyze operator classes.

Abstract

We introduce a classification of simple, regular, closed symmetric operators with deficiency indices (1,1) according to a geometric criterion that extends the classical notions of entire operators and entire operators in the generalized sense due to M. G. Krein. We show that these classes of operators have several distinctive properties, some of them related to the spectra of their canonical selfadjoint extensions. In particular, we provide necessary and sufficient conditions on the spectra of two canonical selfadjoint extensions of an operator for it to belong to one of our classes. Our discussion is based on some recent results in the theory of de Branges spaces.