Poisson approximation for the number of visits to balls in nonuniformly hyperbolic dynamical systems

We study the number of visits to balls B_r(x), up to time t/mu(B_r(x)), for a class of non-uniformly hyperbolic dynamical systems, where mu is the SRB measure. Outside a set of `bad’ centers x, we prove that this number is approximately Poissonnian with a controlled error term. In particular, when r–>0, we get convergence to the Poisson law for a set of centers of mu-measure one. Our theorem applies for instance to the H'enon attractor and, more generally, to systems modelled by a Young tower whose return-time function has a exponential tail and with one-dimensional unstable manifolds. Along the way, we prove an abstract Poisson approximation result of independent interest.