English

Compact perturbations and consequent hereditarily polaroid operators

Functional Analysis 2015-11-05 v1

Abstract

A Banach space operator AB(X)A\in B({\cal{X}}) is polaroid, APA\in {\cal{P}}, if the isolated points of the spectrum σ(A)\sigma(A) are poles of the operator; AA is hereditarily polaroid, AHPA\in{\cal{HP}}, if every restriction of AA to a closed invariant subspace is polaroid. Operators AHPA\in{\cal{HP}} have SVEP on Φsf(A)={λ:Aλ\Phi_{sf}(A)=\{\lambda: A-\lambda is semi Fredholm }\}: This, in answer to a question posed by Li and Zhou (Studia Math. 221(2014), 175-192), proves the necessity of the condition Φsf+(A)=\Phi_{sf}^+(A)=\emptyset. A sufficient condition for AB(X)A\in B({\cal{X}}) to have SVEP on Φsf(A)\Phi_{sf}(A) is that its component Ωa(A)={λΦsf(A):ind(Aλ)0}\Omega_a(A)=\{\lambda\in\Phi_{sf}(A): \rm{ind}(A-\lambda)\leq 0\} is connected. We prove: If AB(H)A\in B({\cal{H}}) is a Hilbert space operator, then a necessary and sufficient condition for there to exist a compact operator KK such that A+KHPA+K\in{\cal{HP}} is that Ωa(A)\Omega_a(A) is connected.

Keywords

Cite

@article{arxiv.1511.01408,
  title  = {Compact perturbations and consequent hereditarily polaroid operators},
  author = {B. P. Duggal},
  journal= {arXiv preprint arXiv:1511.01408},
  year   = {2015}
}

Comments

10 Pages

R2 v1 2026-06-22T11:37:37.373Z