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arXiv · 2610.01043

Extreme points of the unit ball and isometries of noncommutative quasi-Banach Marcinkiewicz spaces

Kai Fang·Yi Gao·Jinghao Huang·Fedor Sukochev
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Abstract

We characterize extreme points of the (positive) unit ball of Marcinkiewicz spaces with respect to their natural quasi-norms. Having these results at hand, we show that every positive isometry on a noncommutative Marcinkiewicz space is of elementary form. In particular, a linear mapping on a noncommutative Marcinkiewicz space over an atomic von Neumann algebra with all atoms having the same trace is a positive surjective isometry if and only if it is the restriction of a Jordan $*$-isomorphism which preserves the singular value functions. We also study (not necessarily positive) surjective isometries on weak $L_p$-spaces affiliated a $σ$-finite non-atomic von Neumann algebra for $1 0$, as well as one-parameter groups of isometries on the latter two.

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Kai Fang, Yi Gao, Jinghao Huang, Fedor Sukochev. 2026-10-01. Extreme points of the unit ball and isometries of noncommutative quasi-Banach Marcinkiewicz spaces. https://arxiv.org/abs/2610.01043

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