Domain deformations and eigenvalues of the Dirichlet Laplacian in a Riemannian manifold

Abstract

For any bounded regular domain $\Omega$ of a real analytic Riemannian manifold $M$ we denote by $\lambda_{k}(\Omega)$ the $k$-th eigenvalue of the Dirichlet Laplacian of $\Omega$. In this paper, we consider $\lambda_k$ as a functional on the set of domains of fixed volume in $M$. We introduce and investigate a natural notion of critical domain for this functional. In particular, we obtain necessary and sufficient conditions for a domain to be critical, locally minimizing or locally maximizing for $\lambda_k$. These results rely on Hadamard type variational formulae that we establish in this general setting. As an application, we obtain a characterization of critical domains of the trace of the heat kernel under Dirichlet boundary conditions.