Absolute continuity, Lyapunov exponents and rigidity I : geodesic flows

Abstract

We consider volume-preserving perturbations of the time-one map of the geodesic flow of a compact surface with negative curvature. We show that if the Liouville measure has Lebesgue disintegration along the center foliation then the perturbation is itself the time-one map of a smooth volume-preserving flow, and that otherwise the disintegration is necessarily atomic.

29 pages. Small error in statement of Theorem A corrected from previous version ("k points" replaced by "k orbits")