Codimension-5 conjecture for noncollapsed Einstein 5-manifold limits

Let (X,d)(X,d) be a Gromov–Hausdorff limit of noncollapsed Einstein 55-manifolds. Let Rorb\mathcal{R}_{\mathrm{orb}} be the orbifold regular set and define the orbifold singular set by

Sorb=XRorb.\mathcal{S}_{\mathrm{orb}}=X\setminus\mathcal{R}_{\mathrm{orb}}.

Codimension-5 conjecture. The set Sorb\mathcal{S}_{\mathrm{orb}} is countable. In particular, away from a countable set of points, (X,d)(X,d) has the structure of a smooth Einstein 55-orbifold with singularities of the form R×R4/Γ\mathbb{R}\times\mathbb{R}^4/\Gamma along countably many geodesics. This conjecture would follow essentially from ruling out accumulation of singular points not lying on curves of the singular set, and it proposes an orbifold regularity theory off a codimension-55 set.

Sources & referencesView supporting material

Primary source

Yiqi Huang and Tristan Ozuch, “Regularity of Einstein 5-manifolds via 4-dimensional gap theorems”, arXiv:2512.21317 (2026).

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