On eigenvalue inequalities of Schmuckenschlager

Abstract

About ten years ago, Schmuckenschläger proved that the lowest eigenvalue of Dirichlet Laplacian for the intersection of two balls (i.e., convex, symmetric and compact subsets of $\mathbb{R}^n$ with non-empty interior) is less than the sum of the lowest eigenvalue for each. His arguments rely on Kac's formula, the log-concavity of Gaussian measures, the symmetry of balls and Lieb's classical result for the intersection of two domains. In this note we revisit Schmuckenschläger's proof and propose a direct and elementary Lieb-free approach to these inequalities.