Milman's spectral conjecture for positively Ricci-curved spheres

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Let dd be a positive integer, let (Sd,g)(\mathbb{S}^d,g) be a Riemannian sphere, and let vol⁡g\operatorname{vol}_g denote its volume measure. Suppose that

Ric⁡g≥ρg\operatorname{Ric}_g\geq \rho g

for some ρ>0\rho>0. Let gcanρg^\rho_{\mathrm{can}} be the canonical metric on Sd\mathbb{S}^d rescaled so that

Ric⁡gcanρ=ρgcanρ.\operatorname{Ric}_{g^\rho_{\mathrm{can}}}=\rho g^\rho_{\mathrm{can}}.

Here λk(Sd,g,vol⁡g)\lambda_k(\mathbb{S}^d,g,\operatorname{vol}_g) denotes the kkth eigenvalue in the relevant weighted spectral problem. Milman's spectral conjecture. For every k≥1k\geq 1,

λk(Sd,g,vol⁡g)≥λk(Sd,gcanρ,vol⁡gcanρ).\lambda_k(\mathbb{S}^d,g,\operatorname{vol}_g)\geq\lambda_k(\mathbb{S}^d,g^\rho_{\mathrm{can}},\operatorname{vol}_{g^\rho_{\mathrm{can}}}).

This is one of Milman's proposed finite-dimensional extensions of the Gaussian contraction paradigm. The paper states that its corresponding conjecture is false in general, so this spectral claim is refuted.

References

Primary source

Shrey Aryan, “Spectral Obstructions to Contracting Transport Maps on Curved Spaces”, arXiv:2605.24705 (2026).

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