Spectral properties of elementary operators. II

Abstract

Let A = (Ai,..., A") and B = (Bj,..., Bn) denote commutative n-tuples of operators on a Hubert space W. Let Rab denote the elementary operator on L(U) defined by Rab{X) = A1XB1 4--hA"XB".We obtain new expressions for the essential spectra of Rab and Rab\J (the restriction of Rab to a norm ideal J of (W)).We also study isolated points of joint spectra defined in the sense of R. Harte.