Amadeu Delshams,Rafael de la Llave, Tere M.~Seara A geometric mechanism for diffusion in Hamiltonian systems overcoming the large gap problem: Announcement of results (995K, PS) ABSTRACT. We present a geometric mechanism for diffusion in Hamiltonian systems. We also present tools that allow to verify it in a concrete model. In particular, we verify it in a system which presents the large gap problem.