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Scalar and Mean Curvature Comparison on Compact Cylinder

Differential Geometry 2025-07-10 v1

Abstract

Let X X be a closed, oriented Riemannian manifold. Denote by (M=X×I,M=X×{0}X×{1},g) (M = X \times I, \partial M = X \times \lbrace 0 \rbrace \cup X \times \lbrace 1 \rbrace, g) a compact cylinder with smooth boundary, dimM3 \dim M \geqslant 3 . In this article, we address the following question: If g g is a Riemannian metric having (i) positive scalar curvature (PSC metric) on M M and nonnegative mean curvature on M \partial M ; and (ii) the g g -angle between normal vector field νg \nu_{g} along M \partial M and ξΓ(TI) \partial_{\xi} \in \Gamma(TI) being less than π4 \frac{\pi}{4} , then there exists a metric g~ \tilde{g} on M M such that g~X×{0} \tilde{g} |_{X \times \lbrace 0 \rbrace} is a PSC metric on XX×{0} X \cong X \times \lbrace 0 \rbrace . Equivalently, we show that if X X admits no PSC metric, but M M admits a PSC metric g g satisfying the angle condition, then the mean curvature on M \partial M must be negative somewhere. This generalizes a result of Gromov and Lawson (Ann. of Math. (2), 1980) for X=Tn X = \mathbb{T}^{n} .

Keywords

Cite

@article{arxiv.2507.07005,
  title  = {Scalar and Mean Curvature Comparison on Compact Cylinder},
  author = {Jie Xu},
  journal= {arXiv preprint arXiv:2507.07005},
  year   = {2025}
}

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