On the eigenvalues of the Laplacian on fibred manifolds

Abstract

We prove various comparison theorems of the $i$-th eigenvalue ${\lambda }_i$ of the Laplacian on fibred Riemannian manifolds by using fiberwise spherical and Euclidean (or hyperbolic) symmetrization. In particular we generalize the Lichnerowicz inequality and the Faber-Krahn inequality to fiber bundles, and prove a counterpart to Cheng's ${\lambda }_1$ comparison theorem under a lower Ricci curvature bound. By applying these, it is shown that ${\lambda }_1,\cdots ,{\lambda }_k$ of a fiber bundle given by a Riemannian submersion with totally geodesic fibers of sufficiently positive Ricci curvature are respectively equal to ${\lambda }_1,\cdots ,{\lambda }_k$ of its base, and ${\lambda }_1$ of a (possibly singular) fibration with Euclidean subsets as fibers is no less than ${\lambda }_1$ of the disk bundle obtained by replacing each fiber with a Euclidean disk of the same dimension and volume.

arXiv admin note: substantial text overlap with arXiv:2108.12651