Given a Tonelli Hamiltonian of class C 2 on the cotangent bundle of a compact surface, we show that there is an open dense set of potentials in the C 2 topology for which the Aubry set is hyperbolic in its energy level.
IntroductionLet M be a smooth compact Riemannian manifold without boundary of dimension n ≥ 2, and H : T * M → R be a Tonelli Hamiltonian of class C 2 . As shown by Mather [27], one can construct a compact invariant subset of T * M which enjoys several variational properties and has the distinguished feature of being a Lipschitz graph over M . This set, called the Aubry set associated to H and denoted byÃ(H), captures many important features of the Hamiltonian dynamics.Fathi [16] established a bridge between the Aubry-Mather theory and the properties of viscosity solutions/subsolutions of the critical Hamilton-Jacobi equation associated with H, giving rise to the weak KAM theory. The differentials of critical (viscosity) subsolutions are uniquely determined on the projection ofÃ(H) onto M (denoted by A(H)), and all critical subsolutions are indeed C 1,1 on the projected Aubry set A(H). We refer the reader to Section 2.1 below for a precise definition of the Aubry set and more details in weak KAM theory.A famous open problem concerning the structure ofÃ(H) is the so-called "Mañé conjecture" [25] which states that, for a generic Hamiltonian, the Aubry set is either a hyperbolic equilibrium or a hyperbolic periodic orbit. In [19,20], the second and third author obtained several results in the direction of proving the validity of the Mañé conjecture. However, all that results heavily rely on the assumption of the existence of a sufficiently smooth critical (sub-)solution. The goal of this paper is to combine some of the techniques developed in [19,20] Is it true that generically the Aubry set is hyperbolic? As mentioned by Herman at the beginning of [22, Section 6], the subject of the instabilities of Hamiltonian flows and the problem of topological stability "lacks any non-trivial result". Our main theorem solves in the affirmative Herman's problem on surfaces for the C 2 -topology.0 The second and third authors are supported by the program "Project ANR-07-BLAN-0361, Hamilton-Jacobi et théorie KAM faible". AF is also supported by NSF Grants DMS-0969962 and DSM-1262411. GC is supported by CONACYT Grant 178838. LR is also supported by the ANR project GCM, program "Blanche", project number NT09-504490. 1 Theorem 1.1. Let H : T * M → R be a Tonelli Hamiltonian of class C 2 , and assume that dim M = 2. Then there is an open dense set of potentials V ⊂ C 2 (M ) such that, for every V ∈ V, the Aubry set associated to the Hamiltonian H + V is hyperbolic in its energy level.The proof of Theorem 1.1 relies on the properties of Green bundles which can be associated with each orbit of the Aubry set. The basic idea is based on the following dichotomy for Green bundles: either they are always transverse, in which case one gets hyperbolicity of the Aubry set; or the Green bundles coincide along a given or...