Normally hyperbolic invariant manifolds near strong double resonance
  In the present paper we consider a generic perturbation of a nearly integrable system of $n$ and a half degrees of freedom $ H_\epsilon(\theta,p,t)=H_0(p)+\epsilon H_1(\theta,p,t)$, with a strictly convex $H_0$. For $n=2$ we show that at a strong double resonance there exist 3-dimensional normally hyperbolic invariant cylinders going across. This is somewhat unexpected, because at a strong double resonance dynamics can be split into one dimensional fast motion and two dimensional slow motion. Slow motions are described by a mechanical system on a two-torus, which are generically chaotic.   The construction of invariant cylinders involves finitely smooth normal forms, analysis of local transition maps near singular points by means of Shilnikov's boundary alue problem, and Conley--McGehee's isolating block. 
Vadim Kaloshin and Ke Zhang
math.DS