Almost nonnegative curvature operator Betti-number conjecture

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Let mm be a positive integer, and let (Mm,g)(M^m,g) be a compact Riemannian manifold with diameter diam⁡(M)=1\operatorname{diam}(M)=1. Write Rm\mathcal{R}m for its curvature operator, and let bi(M)\text{b}_i(M) denote its ii-th Betti number. Almost nonnegative curvature operator Betti-number conjecture. There exists an ϵ(m)>0\epsilon(m)>0 such that, if

Rm≥−ϵg⊙g,\mathcal{R}m\ge -\epsilon g\odot g,

then

bi(M)≤(mi).\text{b}_i(M)\le \binom{m}{i}.

Moreover, equality holds if and only if MM is diffeomorphic to a torus. The conjecture proposes a stability version of the equality statement for compact manifolds with nonnegative curvature operator; the source gives no resolution, so its status remains open.

References

Primary source

Xin Peng, Bing Wang and Zhenjian Wang, “Structure of Torus Fibration Under the First Betti Number Restriction”, arXiv:2605.11552 (2026).

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