There are no deviations for the ergodic averages of the Giulietti-Liverani horocycle flows on the two-torus
Résumé
We show that the ergodic averages for the horocycle flow on the two-torus associated by Giulietti and Liverani to an Anosov diffeomorphism either grow linearly or are bounded, in other words there are no deviations. For this, we use topological invariance of the Artin-Mazur zeta function to exclude resonances outside of the open unit disc. Transfer operators acting on suitable spaces of anisotropic distributions and their Ruelle determinants are the key tools in the proof. As a bonus, we show that for any smooth Anosov diffeomorphism F on the two-torus, the correlations for the measure of maximal entropy and smooth observables decay with a rate strictly smaller than exp(-h_top(F)). We compare our results with related work of Forni.