Operators invariant relative to a completely nonunitary contraction

Given a contraction A on a Hilbert space H, an operator T on H is said to be A-invariant if = for every x in H such that ||Ax||=||x||. In the special case in which both defect indices of A are equal to 1, we show that every A-invariant operator is the compression to H of an unbounded linear transfor...

Full description

Saved in:
Bibliographic Details
Published in:arXiv.org 2017-04
Main Authors: Bercovici, H, Timotin, D
Format: Article
Language:English
Subjects:
Hilbert space
Invariants
Linear transformations
Operators
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Given a contraction A on a Hilbert space H, an operator T on H is said to be A-invariant if = for every x in H such that ||Ax||=||x||. In the special case in which both defect indices of A are equal to 1, we show that every A-invariant operator is the compression to H of an unbounded linear transformation that commutes with the minimal unitary dilation of A. This result was proved by Sarason under the additional hypothesis that A is of class C_{00}, leading to an intrinsic characterization of the truncated Toeplitz operators. We also adapt to our more general context other results about truncated Toeplitz operators.
ISSN:2331-8422