English

Measures of noncompactness in Hilbert $C^*$-modules

Operator Algebras 2024-09-05 v1 Functional Analysis

Abstract

Consider a countably generated Hilbert CC^*-module M\mathcal M over a CC^*-algebra A\mathcal A. There is a measure of noncompactness λ\lambda defined, roughly as the distance from finitely generated projective submodules, which is independent of any topology. We compare λ\lambda to the Hausdorff measure of noncompactness with respect to the family of seminorms that induce a topology recently iontroduced by Troitsky, denoted by χ\chi^*. We obtain λχ\lambda\equiv\chi^*. Related inequalities involving other known measures of noncompactness, e.g. Kuratowski and Istr\u{a}\c{t}escu are laso obtained as well as some related results on adjontable operators.

Keywords

Cite

@article{arxiv.2409.02514,
  title  = {Measures of noncompactness in Hilbert $C^*$-modules},
  author = {Dragoljub J. Kečkić and Zlatko Lazović},
  journal= {arXiv preprint arXiv:2409.02514},
  year   = {2024}
}

Comments

14 pages

R2 v1 2026-06-28T18:33:41.213Z