LAUSR

Let $${T : M \to M}$$T:M→M be a nonuniformly expanding dynamical system, such as logistic or intermittent map. Let $${v : M \to \mathbb{R}^d}$$v:M→Rd be an observable and $${v_n = \sum_{k=0}^{n-1} v \circ T^k}$$vn=∑k=0n-1v∘Tk denote the Birkhoff sums. Given a probability measure $${\mu}$$μ on M, we consider vn as a discrete time random process on the probability space $${(M, \mu)}$$(M,μ). In smooth ergodic theory there are various natural choices of $${\mu}$$μ, such as the Lebesgue measure, or the absolutely continuous T-invariant measure. They give rise to different random processes. We investigate relation between such processes. We show that in a large class of measures, it is possible to couple (redefine on a new probability space) every two processes so that they are almost surely close to each other, with explicit estimates of “closeness”. The purpose of this work is to close a gap in the proof of the almost sure invariance principle for nonuniformly hyperbolic transformations by Melbourne and Nicol.