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The degree condition in Llarull's theorem on scalar curvature rigidity

Differential Geometry 2026-04-17 v2

Abstract

Llarull's scalar curvature rigidity theorem states that a 1-Lipschitz map f:MSnf: M\to S^n from a closed connected Riemannian spin manifold MM with scalar curvature scaln(n1)\mathrm{scal}\ge n(n-1) to the standard sphere SnS^n is an isometry if the degree of ff is nonzero. We investigate if one can replace the condition deg(f)0\mathrm{deg}(f)\neq0 by the weaker condition that ff is surjective. The answer turns out to be "no" for n3n\ge3 but "yes" for n=2n=2. If we replace the scalar curvature by Ricci curvature, the answer is "yes" in all dimensions.

Keywords

Cite

@article{arxiv.2507.05459,
  title  = {The degree condition in Llarull's theorem on scalar curvature rigidity},
  author = {Christian Baer and Rudolf Zeidler},
  journal= {arXiv preprint arXiv:2507.05459},
  year   = {2026}
}

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