Rates in almost sure invariance principle for nonuniformly hyperbolic maps

TL;DR

This paper establishes the Almost Sure Invariance Principle with near-optimal error rates for a broad class of nonuniformly hyperbolic maps, including systems with slow mixing and flat points, extending previous results.

Contribution

It proves the ASIP for nonuniformly hyperbolic maps without assuming exponential contraction, covering new systems like billiards with flat points and falling balls.

Findings

ASIP with near-optimal error rates for nonuniformly hyperbolic maps.

Includes systems with slow mixing and flat points previously not covered.

Uses a novel approach building on renewal Markov shifts and full trajectory observables.

Abstract

We prove the Almost Sure Invariance Principle (ASIP) with close to optimal error rates for nonuniformly hyperbolic maps. We do not assume exponential contraction along stable leaves, therefore our result covers in particular slowly mixing invertible dynamical systems as Bunimovich flowers, billiards with flat points as in Chernov and Zhang (2005) and Wojtkowski' (1990) system of two falling balls. For these examples, the ASIP is a new result, not covered by prior works for various reasons, notably because in absence of exponential contraction along stable leaves, it is challenging to employ the so-called Sinai's trick (Sinai 1972, Bowen 1975) of reducing a nonuniformly hyperbolic system to a nonuniformly expanding one. Our strategy follows our previous papers on the ASIP for nonuniformly expanding maps, where we build a semiconjugacy to a specific renewal Markov shift and adapt the argument of Berkes, Liu and Wu (2014). The main difference is that now the Markov shift is two-sided, the observables depend on the full trajectory, both the future and the past.