
arXiv: 2402.05834
A closed connected oriented Riemannian manifold $N$ with non-vanishing Euler characteristic, non-negative curvature operator and $0< 2\text{Ric}_N<\text{scal}_N$ is area-rigid in the sense that any area non-increasing spin map $f\colon M\to N$ from a closed connected oriented Riemannian manifold $M$ with non-vanishing $\hat{A}$-degree and $\text{scal}_M\geq \text{scal}_N \circ f$ is a Riemannian submersion with $\text{scal}_M=\text{scal}_N \circ f$. This is due to Goette and Semmelmann and generalizes a result by Llarull. In this article, we show area-rigidity for not necessarily orientable manifolds with respect to a larger class of maps $f\colon M\to N$ by replacing the topological condition on the $\hat{A}$-degree by a less restrictive condition involving the so-called higher mapping degree. This includes fiber bundles over even dimensional spheres with enlargeable fibers, e.g. $\text{pr}_1\colon S^{2n}\times T^k \to S^{2n}$. We develop a technique to extract from a non-vanishing higher index a geometrically useful family of almost $\mathcal{D}$-harmonic sections. This also leads to a new proof of the fact that any closed connected spin manifold with non-negative scalar curvature and non-trivial Rosenberg index is Ricci flat.
36 pages, 3 figures; v2: minor improvements; To appear in J. Funct. Anal
Mathematics - Differential Geometry, Global geometric and topological methods (à la Gromov); differential geometric analysis on metric spaces, Dirac operator, higher index theory, Rigidity results, Spin and Spin\({}^c\) geometry, comparison geometry, Geometric Topology (math.GT), K-Theory and Homology (math.KT), scalar curvature rigidity, Mathematics - Geometric Topology, Differential Geometry (math.DG), Mathematics - K-Theory and Homology, FOS: Mathematics, Index theory and related fixed-point theorems on manifolds
Mathematics - Differential Geometry, Global geometric and topological methods (à la Gromov); differential geometric analysis on metric spaces, Dirac operator, higher index theory, Rigidity results, Spin and Spin\({}^c\) geometry, comparison geometry, Geometric Topology (math.GT), K-Theory and Homology (math.KT), scalar curvature rigidity, Mathematics - Geometric Topology, Differential Geometry (math.DG), Mathematics - K-Theory and Homology, FOS: Mathematics, Index theory and related fixed-point theorems on manifolds
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