Hyponormality and spectra of Toeplitz operators

Author:

Farenick Douglas,Lee Woo

Abstract

This paper concerns algebraic and spectral properties of Toeplitz operators T φ T_{\varphi } , on the Hardy space H 2 ( T ) H^{2}({\mathbb {T}}) , under certain assumptions concerning the symbols φ L ( T ) \varphi \in L^{\infty }({\mathbb {T}}) . Among our algebraic results is a characterisation of normal Toeplitz opertors with polynomial symbols, and a characterisation of hyponormal Toeplitz operators with polynomial symbols of a prescribed form. The results on the spectrum are as follows. It is shown that by restricting the spectrum, a set-valued function, to the set of all Toeplitz operators, the spectrum is continuous at T φ T_{\varphi } , for each quasicontinuous φ \varphi . Secondly, we examine under what conditions a classic theorem of H. Weyl, which has extensions to hyponormal and Toeplitz operators, holds for all analytic functions of a single Toeplitz operator with continuous symbol.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference27 articles.

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