Almost nonnegative curvature operator Betti-number conjecture

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

Rmϵgg,\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.

Sources & referencesView supporting material

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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