Principal eigenvalues for k-Hessian operators by maximum principle methods

For fully nonlinear k-Hessian operators on bounded strictly (k-1)-convex domains Omega of N-domennsional Euclidian space, a characterization of the principal eigenvalue associated to a k-convex and negative principal eigenfunction will be given as the supremum over values of a spectral parameter for which {em admissible viscosity supersolutions} obey a minimum principle. The admissibility condition is phrased in terms of the natural closed convex cone (in the sèace of symmetric NxN matrices) which is an elliptic set in the sense of Krylov (Trans. AMS, 1995) which corresponds to using k-convex functions as admissibility constraints in the formulation of viscosity subsolutions and supersolutions. Moreover, the associated principal eigenfunction is constructed by an iterative viscosity solution technique, which exploits a compactness property which results from the establishment of a global Hoelder estimate for the unique k-convex solutions of the approximating equations.