On the Unstable Directions and Lyapunov Exponents of Anosov Endomorphisms

Abstract

Despite the invertible setting, Anosov endomorphisms may have infinitely many unstable directions. Here we prove, under transitivity assumption, that an Anosov endomorphism on a closed manifold $M,$ is either special (that is, every $x\in M$ has only one unstable direction) or for a typical point in $M$ there are infinitely many unstable directions. Other result of this work is the semi rigidity of the unstable Lyapunov exponent of a $C^{1+\alpha }$ codimension one Anosov endomorphism and $C^1$ close to a linear endomorphism of ${\mathbb{T}}^n$ for $(n\ge 2).$ In the appendix we give a proof for ergodicity of $C^{1+\alpha },\alpha >0,$ conservative Anosov endomorphism.