Diffeomorphisms with positive metric entropy
  We obtain a dichotomy for $C^1$-generic, volume-preserving diffeomorphisms: either all the Lyapunov exponents of almost every point vanish or the volume is ergodic and non-uniformly Anosov (i.e. nonuniformly hyperbolic and the splitting into stable and unstable spaces is dominated). This completes a program first put forth by Ricardo Ma\~n\'e. 
Artur Avila, Sylvain Crovisier and Amie Wilkinson
math.DS