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JOURNALS // Funktsional'nyi Analiz i ego Prilozheniya // Archive

Funktsional. Anal. i Prilozhen., 2020 Volume 54, Issue 4, Pages 74–84 (Mi faa3809)

This article is cited in 4 papers

Compact Operators and Uniform Structures in Hilbert $C^*$-Modules

E. V. Troitskiiab, D. V. Fufaevab

a Moscow Center for Fundamental and Applied Mathematics, Moscow, Russia
b Department of Mechanics and Mathematics, Lomonosov Moscow State University, Moscow, Russia

Abstract: Quite recently a criterion for the $\mathcal{A}$-compactness of an ajointable operator $F\colon\M\to\mathcal{N}$ between Hilbert $C^*$-modules, where $\mathcal{N}$ is countably generated, was obtained. Namely, a uniform structure (a system of pseudometrics) in $\mathcal{N}$ was discovered such that $F$ is $\mathcal{A}$-compact if and only if $F(B)$ is totally bounded, where $B\subset\M$ is the unit ball.
We prove that (1) for a general $\mathcal{N}$, $\mathcal{A}$-compactness implies total boundedness, (2) for $\mathcal{N}$ with $\mathcal{N}\oplus K\cong L$, where $L$ is an uncountably generated $\ell_2$-type module, total boundedness implies compactness, and (3) for $\mathcal{N}$ close to be countably generated, it suffices to use only pseudometrics of “frame-like origin” to obtain a criterion for $\mathcal{A}$-compactness.

Keywords: Hilbert $C^*$-Module, uniform structure, totally bounded set, compact operator, $\mathcal{A}$-compact operator, frame.

UDC: 917.98

Received: 15.06.2020
Revised: 15.07.2020
Accepted: 21.07.2020

DOI: 10.4213/faa3809


 English version:
Functional Analysis and Its Applications, 2020, 54:4, 287–294

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© Steklov Math. Inst. of RAS, 2024