Semi-Fredholm theory in C*-algebras
Abstract
Keckic and Lazovic introduced an axiomatic approach to Fredholm theory by considering Fredholm-type elements in an unital C*-algebra as a generalization of C*-Fredholm operators on the standard Hilbert C*-module introduced by Mishchenko and Fomenko and of Fredholm operators on a properly infinite von Neumann algebra introduced by Breuer. In this paper, we establish the semi-Fredholm theory in unital C*-algebras as a continuation of the approach by Keckic and Lazovic. We introduce the notion of semi-Fredholm-type elements and semi-Weyl-type elements. We prove that the difference between the set of semi-Fredholm elements and the set of semi-Weyl elements is open in the norm topology, that the set of semi-Weyl elements is invariant under perturbations by finite type elements, and several other results generalizing their classical counterparts. Also, we illustrate applications of our results to the special case of properly infinite von Neumann algebras and we obtain a generalization of the punctured neighborhood theorem in this setting.
Keywords
Cite
@article{arxiv.2002.04905,
title = {Semi-Fredholm theory in C*-algebras},
author = {Stefan Ivkovic},
journal= {arXiv preprint arXiv:2002.04905},
year = {2023}
}
Comments
This preprint has not undergone peer review (when applicable) or any post-submission improvements or corrections. The Version of the Record of this article is published in the Banach Journal of Mathematical Analysis and is available online at https://doi.org/10.1007/s43037-023-00277-y