Extended flexibility of Lyapunov exponents for Anosov diffeomorphisms

TL;DR

This paper extends the understanding of Lyapunov exponent flexibility in conservative Anosov diffeomorphisms, introducing new deformation techniques and providing examples where exponents surpass linear bounds, with implications for entropy and robustness.

Contribution

It introduces a novel deformation method for conservative Anosov diffeomorphisms, demonstrating extended Lyapunov exponent flexibility beyond previous techniques.

Findings

Examples with unstable exponents larger than linear parts.

Examples with entropy exceeding linear entropy.

Lyapunov exponents are continuous and robust under perturbations.

Abstract

Bochi-Katok-Rodriguez Hertz proposed in [BKH21] a program on the flexibility of Lyapunov exponents for conservative Anosov diffeomorphisms, and obtained partial results in this direction. For conservative Anosov diffeomorphisms with strong hyperbolic properties we establish extended flexibility results for their Lyapunov exponents. We give examples of Anosov diffeomorphisms with the strong unstable exponent larger than the strong unstable exponent of the linear part. We also give examples of derived from Anosov diffeomorphisms with the metric entropy entropy larger than the entropy of the linear part. These results rely on a new type of deformation which goes beyond the previous Shub-Wilkinson and Baraviera-Bonatti techniques for conservative systems having some invariant directions. In order to estimate the Lyapunov exponents even after breaking the invariant bundles, we obtain an abstract result (Theorem 3.1) which gives bounds on exponents of some specific cocycles and which can be applied in various other settings. We also include various interesting comments in the appendices: our examples are $\mathcal{C}^2$ robust, the Lyapunov exponents are continuous (with respect to the map) even after breaking the invariant bundles, a similar construction can be obtained for the case of multiple eigenvalues.