Rigidit\'e, expansion et entropie en dynamique non-archim\'edienne (Rigidity, expansion and entropy in non-Archimedean dynamics)

Abstract

We prove a rigidity property in non-Archimedean dynamics, reminiscent of Zdunik theorem in complex dynamics: every rational map whose equilibrium measure charges an interval in the Berkovich projective line is affine Bernoulli. Our proof is inspired by the construction of the affine model of multimodal maps by Parry and by Milnor and Thurston. This rigidity result allows us to show that the topological entropy of any tame rational map is the logarithm of an integer. To that end we analyze the properties of the multiplicative (sub)coboundary given by the spherical derivative and we establish a link between the sign of the Lyapunov exponent and the locus of wild ramification.