Sublacunary sequences that are strong sweeping out

Abstract

An increasing sequence $(a_n)$ of positive integers which satisfies $\frac{a_{n+1}}{a_n}>1+\eta$ for some positive $\eta$ is called a lacunary sequence. It has been known for over twenty years that every lacunary sequence is strong sweeping out which means that in every aperiodic dynamical system we can find a set $E$ of arbitrary small measure so that $\limsup_N\frac{1}{N} \sum_{n\le N}\mathbb{1}_E(T^nx)=1$ and $\liminf_N\frac{1}{N} \sum_{n\le N}\mathbb{1}_E(T^nx)=0$ almost everywhere. In this paper we improve this result by showing that if $(a_n)$ satisfies only $\frac{a_{n+1}}{a_n}>1+\frac1{(\log\log n)^{1-\eta}}$ for some positive $\eta$ then it is already strong sweeping out.