Horizontal diameter rigidity conjecture for singular Riemannian foliations on spheres

Let F\mathcal{F} be a singular Riemannian foliation on the unit sphere Sn\mathbb{S}^{n}. A curve is horizontal if it meets the leaves of F\mathcal{F} perpendicularly, and dH(p,q)d_{\mathcal{H}}(p,q) denotes the infimum of the lengths of horizontal curves joining pp and qq. Define the horizontal diameter by

diamHSn=sup{dH(p,q)p,qSn}.diam_{\mathcal{H}}\mathbb{S}^{n}=\sup\{d_{\mathcal{H}}(p,q)\mid p,q\in\mathbb{S}^{n}\}.

Horizontal diameter rigidity conjecture. For any singular Riemannian foliation on a unit sphere Sn\mathbb{S}^{n}, we have

diamHSn=π.diam_{\mathcal{H}}\mathbb{S}^{n}=\pi.

This asserts that the horizontal geometry of every singular Riemannian foliation on a round unit sphere has the same diameter as the sphere's antipodal distance. The result was proved for many classes of foliations, but the general case remains open in the supplied context.

Sources & referencesView supporting material

Primary source

Yi Shi, “Horizontal diameter of unit spheres with polar foliations and infinitesimally polar actions”, arXiv:1907.12442 (2021).

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