A diffeomorphism f has a C 1 -robust homoclinic tangency if there is a C 1 -neighbourhood U of f such that every diffeomorphism in g ∈ U has a hyperbolic set Λ g , depending continuously on g, such that the stable and unstable manifolds of Λ g have some non-transverse intersection. For every manifold of dimension greater than or equal to three, we exhibit a local mechanism (blender-horseshoes) generating diffeomorphisms with C 1 -robust homoclinic tangencies.Using blender-horseshoes, we prove that homoclinic classes of C 1 -generic diffeomorphisms containing saddles with different indices and that do not admit dominated splittings (of appropriate dimensions) display C 1 -robust homoclinic tangencies.keywords: chain recurrence set, dominated splitting, heterodimensional cycle, homoclinic class, homoclinic tangency, hyperbolic set.MSC 2000: 37C05, 37C20, 37C25, 37C29, 37C70.1 Introduction
Framework and general settingA homoclinic tangency is a dynamical mechanism which is at the heart of a great variety of non-hyperbolic phenomena: persistent coexistence of infinitely many sinks [22], Hénon-like strange attractors [5,20], super-exponential growth of the number of periodic points [19], and non-existence of symbolic extensions [15], among others. Moreover, homoclinic bifurcations (homoclinic tangencies and heterodimensional cycles) are conjectured to be the main source of non-hyperbolic dynamics (Palis denseness conjecture, see [23]).In this paper, we present a local mechanism generating C 1 -robust homoclinic tangencies. Using this construction, we show that the occurrence of robust tangencies is a quite general phenomenon in the non-hyperbolic setting, specially when the dynamics does not admit a suitable dominated splitting. * This paper was partially supported by CNPq, Faperj, and PRONEX (Brazil) and the Agreement in Mathematics Brazil-France. We acknowledge the warm hospitality of I.M.P.A, Institute de Mathématiques de Bourgogne, and PUC-Rio during the stays while preparing this paper 1 Let us now give some basic definitions (in Section 2, we will state precisely the definitions involved in this paper). A transitive hyperbolic set Λ has a homoclinic tangency if there is a pair of points x, y ∈ Λ such that the stable leaf W s (x) of x and the unstable leaf W u (y) of y have some non-transverse intersection Given a hyperbolic set Λ of a diffeomorphism f , for g close to f , we denote by Λ g the hyperbolic set of g which is the continuation of Λ (i.e., Λ g is close to Λ and the dynamics of f on Λ and g on Λ g are conjugate).
Definition 1.1 (Robust cycles).• Robust homoclinic tangencies: A transitive hyperbolic set Λ of a C r -diffeomorphism f has a C r -robust homoclinic tangency if there is a C r -neighborhood N of f such that for every g ∈ N the continuation Λ g of Λ for g has a homoclinic tangency.• Robust heterodimensional cycles: A diffeomorphism f has a C r -robust heterodimensional cycle if there are transitive hyperbolic sets Λ and Σ of f whose stable bundles have different dimensions and a C r -n...