A starlike 3-dimensional counterexample to the hot spots conjecture

Abstract

We construct a bounded Lipschitz domain in ${\mathbb{R}}^3$ that is starlike about the origin and whose first positive Neumann eigenvalue is simple. A corresponding eigenfunction, after a choice of sign, has its unique global maximum at the origin. The construction uses domains with increasingly fine angular structure and convergence to a weighted eigenvalue problem whose first positive eigenfunction is radial.