Closed nodal lines and interior hot spots of the second eigenfunction of the Laplacian on surfaces

الأصل · EN

We build a one-parameter family of S¹-invariant metrics on the unit disc with fixed total area for which the second eigenvalue of the Laplace operator in the case of both Neumann and Dirichlet boundary conditions is simple and has an eigenfunction with a closed nodal line. In the case of Neumann boundary conditions, we also prove that this eigenfunction attains its maximum at an interior point, and thus provide a counterexample to the hot spots conjecture on a simply connected surface. This is a consequence of the stronger result that within this family of metrics any given (finite) number of S¹-invariant eigenvalues can be made to be arbitrarily small, while the non-invariant spectrum becomes arbitrarily large.