P\'{o}lya-type inequalities on spheres and hemispheres

TL;DR

This paper investigates Pólya-type inequalities for Laplace-Beltrami eigenvalues on spheres and hemispheres, characterizing when Pólya's conjecture holds or fails, and deriving bounds that measure deviations from Weyl asymptotics.

Contribution

It provides a detailed analysis of Pólya's conjecture on spheres and hemispheres, including conditions for its validity and new inequalities with sharp bounds.

Findings

Pólya's conjecture holds for hemispheres with Neumann boundary conditions.

Pólya's conjecture fails for Dirichlet conditions on spheres when dimension exceeds two.

Derived inequalities offer sharp bounds and measure deviations from Weyl asymptotics.

Abstract

Given an eigenvalue $\lambda$ of the Laplace-Beltrami operator on $n-$spheres or $-$hemispheres, with multiplicity $m$ such that $\lambda=\lambda_{k}=\dots = \lambda_{k+m-1}$, we characterise the lowest and highest orders in the set $\left\{k,\dots,k+m-1\right\}$ for which P\'{o}lya's conjecture holds and fails. In particular, we show that P\'{o}lya's conjecture holds for hemispheres in the Neumann case, but not in the Dirichlet case when $n$ is greater than two. We further derive P\'{o}lya-type inequalities by adding a correction term providing sharp lower and upper bounds for all eigenvalues. This allows us to measure the deviation from the leading term in the Weyl asymptotics for eigenvalues on spheres and hemispheres. As a direct consequence, we obtain similar results for domains which tile hemispheres. We also obtain direct and reversed Li-Yau inequalities for $\mathbb{S}^2$ and $\mathbb{S}^4$, respectively.