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arXiv · 2608.18112

Counterexamples to a conjectured Schatten norm inequality

Zhekai Pang
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Abstract

For $p\geq 1$ and $m\geq 2$, let $c_p(m)$ be the least constant such that \[ \left\|\sum_{k=1}^m A_k\right\|_p \leq c_p(m)\left\|\sum_{k=1}^m |A_k|\right\|_p \] for all square complex matrices. Tang and Zhang recently conjectured a closed formula for $c_p(m)$, obtained from a common-left equiangular rank-one family. We disprove that formula for every $m\geq2$ and every $1<p<2$.

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Zhekai Pang. 2026-06-25. Counterexamples to a conjectured Schatten norm inequality. https://arxiv.org/abs/2608.18112

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