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

Abstract

Llarull's scalar curvature rigidity theorem states that a 1-Lipschitz map $f:M\to S^n$ from a closed connected Riemannian spin manifold $M$ with scalar curvature $\mathrm{scal}\ge n(n-1)$ to the standard sphere $S^n$ is an isometry if the degree of $f$ is nonzero. We investigate if one can replace the condition $\mathrm{deg}(f)\ne 0$ by the weaker condition that $f$ is surjective. The answer turns out to be "no" for $n\ge 3$ but "yes" for $n=2$. If we replace the scalar curvature by Ricci curvature, the answer is "yes" in all dimensions.

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References in corpus (3)

• Rigidity of 3D spherical caps via $\mu$-bubbles
• Scalar curvature rigidity of warped product metrics
• Abstract cone operators and Lipschitz rigidity for scalar curvature on singular manifolds