Eventual negativity of averaged Ricci curvature in higher eigenspaces

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Let VℓV_\ell denote the eigenspace indexed by ℓ\ell in the Zeitlin model on SU(N)SU(N), and let r~ℓ(N)\widetilde{r}_\ell(N) be the averaged Ricci curvature in that eigenspace. Eventual negativity conjecture. For each fixed ℓ>1\ell>1, r~ℓ(N)\widetilde{r}_\ell(N) becomes negative for sufficiently large NN, and

r~ℓ(N)⟶−Hℓ−12as N⟶∞,\widetilde{r}_\ell(N)\longrightarrow-\frac{H_\ell-1}{2}\quad\text{as }N\longrightarrow\infty,

where HℓH_\ell is the ℓth\ell^{\text{th}} harmonic number. Numerical tables and plots exhibit this sign transition and support the stated limit, but no proof or resolution is given.

References

Primary source

Leandro Lichtenfelz, Klas Modin and Stephen C. Preston, “Ricci curvature for hydrodynamics on the sphere”, arXiv:2508.09833 (2025).

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