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Article Dans Une Revue Journal of the American Mathematical Society Année : 2020

On the Measure of Maximal Entropy for Finite Horizon Sinai Billiard Maps

Résumé

The Sinai billiard map $T$ on the two-torus, i.e., the periodic Lorentz gas, is a discontinuous map. Assuming finite horizon, we propose a definition $h_*$ for the topological entropy of $T$. We prove that $h_*$ is not smaller than the value given by the variational principle, and that it is equal to the definitions of Bowen using spanning or separating sets. Under a mild condition of sparse recurrence to the singularities, we get more: First, using a transfer operator acting on a space of anisotropic distributions, we construct an invariant probability measure $\mu_*$ of maximal entropy for $T$ (i.e., $h_{\mu_*}(T)=h_*$), we show that $\mu_*$ has full support and is Bernoulli, and we prove that $\mu_*$ is the unique measure of maximal entropy and it is different from the smooth invariant measure except if all non grazing periodic orbits have multiplier equal to $h_*$. Second, $h_*$ is equal to the Bowen--Pesin--Pitskel topological entropy of the restriction of $T$ to a non-compact domain of continuity. Last, applying results of Lima and Matheus, as upgraded by Buzzi, the map $T$ has at least $C e^{nh_*}$ periodic points of period $n$ for all $n \in \mathbb{N}$.

Dates et versions

hal-01832765 , version 1 (09-07-2018)

Identifiants

Citer

Viviane Baladi, Mark Demers. On the Measure of Maximal Entropy for Finite Horizon Sinai Billiard Maps. Journal of the American Mathematical Society, 2020, 33 (2), pp.381-449. ⟨10.1090/jams/939⟩. ⟨hal-01832765⟩
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