Spectral Fredholm Theory and Transitivity in Banach bimodules

Abstract

In this paper, we extend Fredholm theory in von Neumann algebras established by Breuer to spectral Fredholm theory. We consider 2 by 2 upper triangular operator matrices with coefficients in a von Neumann algebra and give the relationship between the generalized essential spectra in the sense of Breuer of such matrices and of their diagonal entries. Next, we prove that if a generalized Fredholm operator in the sense of Breuer has 0 as an isolated point of its spectrum, then the corresponding spectral projection is finite. Finally, we define the generalized B-Fredholm operator in a von Neumann algebra as a generalization in the sense of Breuer of the classical B-Fredholm operators on Hilbert and Banach spaces. We provide sufficient conditions under which a sum of a generalized B-Fredholm operator and a finite operator in a von Neumann algebra is again a generalized B-Fredholm operator. Finally, motivated by the connections between supercyclicity and semi-Fredholm theory, in the last section of the paper, we characterize disjoint supercyclic and disjoint Furstenberg semi-transitive operators on a large class of Banach bimodules.