Spectra of subnormal pairs

Abstract

In this short note we present an example related to joint spectra of subnormal pairs of bounded operators. A counterexample to the equality between Taylor's spectrum and the closure of the defect spectrum is given. This example is related to the author's modification of N. Sibony's counterexample to Corona Theorem on domains that fail to be strictly pseudoconvex.

Keywords

• subnormal operator
• corona
• joint spectrum