arXiv subjects

Zlatko Lazović

Publications and source records attributed to Zlatko Lazović.

6 recordsLinked to original sources

arXiv2025

Clarkson-McCarthy inequality on a locally compact group

Let $G$ be a locally compact group, $μ$ its Haar measure, $\hat G$ its Pontryagin dual and $ν$ the dual measure. For any $A_θ\in L^1(G;\mathcal C_p)\cap L^2(G;\mathcal C_p)$, ($\mathcal C_p$ is Schatten ideal), and $1<p\le2$ we prove $$\int_{\hat G}\left\|\int_GA_θ\overline{ξ(θ)}\,\mathrm dμ(θ)\right\|_p^q\,\mathrm dν(ξ)\le \left(\int_G\|A_θ\|_p^p\,\mathrm dμ(θ)\right)^{q/p}, $$ where $q=p/(p-1)$. This appears to be a generalization of some earlier obtained inequalities, including Clarkson-McCarthy inequalities (in the case $G=\mathbf Z_2$), and Hausdorff-Young inequality. Some corollaries are also given.

math.FA↗

arXiv2024

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

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

math.OA↗

arXiv2017

Measures of noncompactness on the standard Hilbert $C^*$-module

We define a measure of noncompactness $λ$ on the standard Hilbert $C^*$-module $l^2(\mathcal A)$ over a unital $C^*$-algebra, such that $λ(E)=0$ if and only if $E$ is $\mathcal A$-precompact (i.e.\ it is $\varepsilon$-close to a finitely generated projective submodule for any $\varepsilon>0$) and derive its properties. Further, we consider the known, Kuratowski, Hausdorff and Istrăţescu measure of noncomapctnes on $l^2(\mathcal A)$ regarded as a locally convex space with respect to a suitable topology, and obtain their properties as well as some relationship between them and introduced measure of noncompactness $λ$.

math.OA↗

arXiv2017

Banach-Alaoglu theorem for Hilbert $H^*$-module

We provided an analogue Banach-Alaoglu theorem for Hilbert $H^*$-module. We construct a $Λ$-weak$^*$ topology on a Hilbert $H^*$-module over a proper $H^*$-algebra $Λ$, such that the unit ball is compact with respect to $Λ$-weak$^*$ topology.

math.OA↗

arXiv2016

Compact and "compact" operators on the standard Hilbert module over a $W^*$ algebra

We construct a topology on the standard Hilbert module $l^2(\mathcal A)$ over a unital $W^*$-algebra $\mathcal A$ such that any "compact" operator, (i.e.\ any operator in the norm closure of the linear span of the operators of the form $x\mapsto\left z$) maps bounded sets into totally bounded sets.

math.OA↗

arXiv2015

Fredholm operators on $C^*$-algebras

The aim of this note is to generalize the notion of Fredholm operator to an arbitrary $C^*$-algebra. Namely, we define "finite type" elements in an axiomatic way, and also we define Fredholm type element $a$ as such element of a given $C^*$-algebra for which there are finite type elements $p$ and $q$ such that $(1-q)a(1-p)$ is "invertible". We derive index theorem for such operators. In applications we show that classical Fredholm operators on a Hilbert space, Fredholm operators in the sense of Breuer, Atiyah and Singer on a properly infinite von Neumann algebra, and Fredholm operators on Hilbert $C^*$-modules over an unital $C^*$-algebra in the sense of Mishchenko and Fomenko are special cases of our theory.

math.OA↗