Some remarks on the optimization of eigenvalue problems involving the p-Laplacian

Given a bounded domain Ω ⊂ Rn, numbers p > 1, ∝ ≥ 0 and A ∈ /0, /Ω/], consider the optimization problem: find a subset D ⊂ Ω, of measure A, for which the first eigenvalue of the operator u → - div(/∇u/p-2 ∇u) + ∝ΧD/u/p-2u with the Dirichlet boundary condition is as small as possible. We show that the optimal configuration D is connected with the corresponding positive eigenfunction u in such a way that there exists a number t ≥ 0 for which D = { u ≤ t}. We also give a new proof of symmetry of optimal solutions in the case when Ω is Steiner symmetric and p = 2.