Zhang's unitary-orbit nn-tuple Schatten inequality conjecture

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Let A1,…,An∈MmA_1,\ldots,A_n\in\mathbb{M}_m, and let ∣A∣|A| denote the positive operator (A∗A)1/2(A^*A)^{1/2}. Zhang's conjecture. For p>2p>2, there exist n(n−1)2+1\frac{n(n-1)}{2}+1 unitary matrices UU and Ui,jU_{i,j}, with 1≤i<j≤n1\le i<j\le n, such that

U∣∑i=1nAi∣pU∗+∑1≤i<j≤nUi,j∣Ai−Aj∣pUi,j∗≤np−1∑i=1n∣Ai∣p.U\left|\sum_{i=1}^n A_i\right|^pU^*+\sum_{1\le i<j\le n}U_{i,j}\left|A_i-A_j\right|^pU_{i,j}^*\le n^{p-1}\sum_{i=1}^n|A_i|^p.

For 0<p≤20<p\le2, the inequality is reversed. This is described as a tuple generalization and strengthening of an earlier operator inequality; no resolution is supplied in the source.

References

Primary source

Teng Zhang, “Clarkson–McCarthy type inequalities, part I: _p–_p and _q–_p Schatten p-estimates”, arXiv:2410.21961 (2026).

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