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

Let A1,,AnMmA_1,\ldots,A_n\in\mathbb{M}_m, and let A|A| denote the positive operator (AA)1/2(A^*A)^{1/2}. Zhang's conjecture. For p>2p>2, there exist n(n1)2+1\frac{n(n-1)}{2}+1 unitary matrices UU and Ui,jU_{i,j}, with 1i<jn1\le i<j\le n, such that

Ui=1nAipU+1i<jnUi,jAiAjpUi,jnp1i=1nAip.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<p20<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.

Sources & referencesView supporting material

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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