Regularity of Lyapunov Exponents for Diffeomorphisms with Dominated Splitting

TL;DR

This paper investigates the regularity and differentiability of Lyapunov exponents in families of diffeomorphisms with dominated splittings, providing formulas and applications to entropy and rigidity phenomena.

Contribution

It establishes the regularity of Lyapunov exponents relative to invariant bundle regularities and derives formulas for derivatives under certain conditions.

Findings

Lyapunov exponents are at least as regular as the sum of bundle regularities.

The derivative formulas for Lyapunov exponents are obtained under specific conditions.

Critical points of Lyapunov exponents imply rigidity and structural decompositions.

Abstract

We consider families of diffeomorphisms with dominated splittings and preserving a Borel probability measure, and we study the regularity of the Lyapunov exponents associated to the invariant bundles with respect to the parameter. We obtain that the regularity is at least the sum of the regularities of the two invariant bundles (for regularities in $[0,1]$), and under suitable conditions we obtain formulas for the derivatives. Similar results are obtained for families of flows, and for the case when the invariant measure depends on the map. We also obtain several applications. Near the time one map of a geodesic flow of a surface of negative curvature the metric entropy of the volume is Lipschitz with respect to the parameter. At the time one map of a geodesic flow on a manifold of constant negative curvature the topological entropy is differentiable with respect to the parameter, and we give a formula for the derivative. Under some regularity conditions, the critical points of the Lyapunov exponent function are non-flat (the second derivative is nonzero for some families). Also, again under some regularity conditions, the criticality of the Lyapunov exponent function implies some rigidity of the map, in the sense that the volume decomposes as a product along the two complimentary foliations. In particular for area preserving Anosov diffeomorphisms, the only critical points are the maps smoothly conjugated to the linear map, corresponding to the global extrema.