On the Dirichlet and Serrin Problems for the Inhomogeneous Infinity Laplacian in Convex Domains: Regularity and Geometric Results

Given an open bounded subset Omega of , which is convex and satisfies an interior sphere condition, we consider the pde in Omega, subject to the homogeneous boundary condition u = 0 on a,Omega. We prove that the unique solution to this Dirichlet problem is power-concave (precisely, 3/4 concave) and it is of class C (1)(Omega). We then investigate the overdetermined Serrin-type problem, formerly considered in Buttazzo and Kawohl (Int Math Res Not, pp 237-247, 2011), obtained by adding the extra boundary condition on a,Omega; by using a suitable P-function we prove that, if Omega satisfies the same assumptions as above and in addition contains a ball which touches a,Omega at two diametral points, then the existence of a solution to this Serrin-type problem implies that necessarily the cut locus and the high ridge of Omega coincide. In turn, in dimension n = 2, this entails that Omega must be a stadium-like domain, and in particular it must be a ball in case its boundary is of class C-2.