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A perturbed elementary operator and range-kernel orthogonality
Authors:B. P. Duggal
Affiliation:Department of Mathematics, College of Science UAEU, P.O. Box 17551, Al Ain, United Arab Emirates
Abstract:Let $ B(mathcal{H})$ denote the algebra of operators on a Hilbert $ mathcal{H}$. If $ A_j$ and $ B_jin B(mathcal{H})$ are commuting normal operators, and $ C_j$ and $ D_jin B(mathcal{H})$ are commuting quasi-nilpotents such that $ A_jC_j-C_jA_j=B_jD_j-D_jB_j=0$, then define $ M_j, N_jin B(mathcal{H})$ and $ {mathcal E}, Ein B(B(mathcal{H}))$ by $ M_j=A_j+C_j$, $ N_j=B_j+D_j$, $ {mathcal E}(X)=A_1XA_2+B_1XB_2$ and $ E(X)=M_1XM_2+N_1XN_2$. It is proved that $ E^{-1}(0)subseteq H_0({mathcal E})={mathcal E}^{-1}(0)$ and $ Xin E^{-1}(0)Longrightarrow vertvert Xvertvertleq k textrm{dist}(X, {mathcal E}(B(mathcal{H})))$, where $ kgeq 1$ is some scalar and $ H_0({mathcal E})$ is the quasi-nilpotent part of the operator $ {mathcal E}$.

Keywords:Hilbert space   elementary operator   normal operator   quasi-nilpotent operator   generalized scalar operator   orthogonality
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