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arXiv · 2302.00218

The projection constant for the trace class

Andreas Defant·Daniel Galicer·Martín Mansilla·Mieczysław Mastyło·Santiago Muro
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Abstract

We study the projection constant of the space of operators on $n$-dimensional Hilbert spaces, with the trace norm, $\mathcal S_1(n)$. We show an integral formula for the projection constant of $\mathcal S_1(n)$; namely $ \boldsymbol{\lambda}\big(\mathcal S_1(n)\big) = n \int_{\mathcal U_n} \vert \text{tr}(U) \vert \,dU \,, $ where the integration is with respect to the Haar probability measure on the group $\mathcal U_n$ of unitary operators. Using a probabilistic approach, we derive the limit formula $ \lim_{n\to \infty} \boldsymbol{\lambda}\big(\mathcal S_1(n)\big)/n = \sqrt{\pi}/2\,. $

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Andreas Defant, Daniel Galicer, Martín Mansilla, Mieczysław Mastyło, Santiago Muro. 2023-02-01. The projection constant for the trace class. https://doi.org/10.2140/apde.2025.18.527

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