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Spectral scalar curvature and codimension-two width
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Category:Differential geometry Lean version:not yet
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Spectral scalar curvature, Urysohn width, and macroscopic dimension. Every complete connected smooth boundaryless n-manifold, n ≥ 3, satisfying $-4\Delta+\mathrm{Scal}\ge1$ as a quadratic-form inequality admits a continuous map to a simplicial complex of dimension at most $n-2$ whose entire fibers have diameter bounded only by n in the original metric. This strengthens Gromov's width conclusion to spectral scalar curvature. Universal covers of closed positive-scalar-curvature manifolds also have continuous macroscopic dimension at most $n-2$ for every n ≥ 2.

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released 2026-10-05  |  2 theorems · 6 lemmas · 8 proofs · 10,781 words  |  PLAY LEVEL 1 »  (pdf)
For every n ≥ 4, a complete connected smooth Riemannian n-manifold without boundary satisfying $-4\Delta+\mathop{\mathrm{Scal}}\nolimits \ge1$ as a quadratic-form inequality admits a continuous map to a simplicial complex of dimension at most $n-2$ whose entire fibers have diameter bounded only in terms of n. The bound is measured in the original metric. This extends the uniform Urysohn width theorem from a pointwise scalar-curvature lower bound to a spectral lower bound.
released 2026-10-05  |  1 theorem · 7 lemmas · 11 proofs · 10,039 words  |  PLAY LEVEL 2 »  (pdf)
Every connected complete smooth Riemannian three-manifold without boundary satisfying $-4\Delta+\mathop{\mathrm{Scal}}\nolimits \ge\lambda\gt 0$ as a quadratic-form inequality admits a continuous map to a graph whose entire fibers have diameter at most $500/\sqrt\lambda$ in the original metric. No orientability, spin, compactness, or bounded-geometry assumption is required.
released 2026-09-23  |  PDF only  |  PLAY LEVEL 3 »  (pdf)
We prove the quantitative continuous form of Gromov's scalar-curvature conjecture in every dimension n ≥ 4. Every complete connected smooth boundaryless n-manifold with scalar curvature at least one admits a continuous map to a simplicial complex of dimension at most $n-2$ whose entire fibers have diameter bounded only in terms of n. We also obtain the continuous macroscopic-dimension conclusion for universal covers of closed manifolds with positive scalar curvature in every dimension n ≥ 2.

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