Dimension-free maximal symmetric modulus conjecture

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For Z∈MdZ\in\mathbb{M}_d, define the maximal symmetric modulus by

∣Z∣∨=∣Z∣∨∣Z∗∣.|Z|_{\vee}=|Z|\vee|Z^*|.

For A,B∈MdA,B\in\mathbb{M}_d, consider whether there are unitaries U,V∈MdU,V\in\mathbb{M}_d and a constant c∨(d)c_{\vee}(d) such that

∣A+B∣∨≤c∨(d)(U∣A∣∨U∗+V∣B∣∨V∗).|A+B|_{\vee}\le c_{\vee}(d)\left(U|A|_{\vee}U^*+V|B|_{\vee}V^*\right).

Maximal symmetric modulus conjecture. For every dimension dd, one may choose c∨(d)=1c_{\vee}(d)=1. The assertion would settle the corresponding finite-dimensional question in its strongest proposed form; it is not resolved in the supplied text.

References

Primary source

Jean-Christophe Bourin and Eun-Young Lee, “Averages over matrix unitary orbits and spectral order”, arXiv:2606.15624 (2026).

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