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The projection constant for the trace class

Andreas Defant, Daniel Galicer, Martin Mansilla, Mieczysław Mastyło and Santiago Muro

Vol. 18 (2025), No. 2, 527–548
Abstract

We study the projection constant of the space of operators on n-dimensional Hilbert spaces with the trace norm 𝒮1(n). We show an integral formula for the projection constant of 𝒮1(n); namely, λ(𝒮1(n)) = n𝒰n|tr (U)|dU, where the integration is with respect to the Haar probability measure on the group 𝒰n of unitary operators. Using a probabilistic approach, we derive the limit formula lim nλ(𝒮1(n))n = π2.

Keywords
projection constant, trace class operators, harmonics, local invariants in Banach spaces
Mathematical Subject Classification
Primary: 46B06, 46B07, 47B10
Secondary: 33C55, 43A15, 46G25
Milestones
Received: 29 May 2023
Accepted: 18 February 2024
Published: 5 February 2025
Authors
Andreas Defant
Institut für Mathematik
Carl von Ossietzky Universität Oldenburg
Oldenburg
Germany
Daniel Galicer
Departamento de Matemática
Universidad de Buenos Aires and IMAS-CONICET
Ciudad Universitaria
Buenos Aires
Argentina
Martin Mansilla
Departamento de Matemática
Universidad de Buenos Aires and IMAS-CONICET
Ciudad Universitaria
Buenos Aires
Argentina
Mieczysław Mastyło
Faculty of Mathematics and Computer Science
Adam Mickiewicz University in Poznań
Poznań
Poland
Santiago Muro
Facultad de Cs. Exactas, Ingenieria y Agrimensura
Universidad Nacional de Rosario and CIFASIS-CONICET
Rosario
Argentina

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