Intermediate-scale statistics for real-valued lacunary sequences

We study intermediate-scale statistics for the fractional parts of the sequence $(\alpha a_n{)}_{n=1}^{\mathrm{\infty }}$, where $(a_n{)}_{n=1}^{\mathrm{\infty }}$ is a positive, real-valued lacunary sequence, and $\alpha \in \mathbb{R}$. In particular, we consider the number of elements $S_N(L,\alpha )$ in a random interval of length $L\mathrm{/}N$, where $L=O\left(N^{1-\epsilon }\right)$, and show that its variance (the number variance) is asymptotic to $L$ with high probability w.r.t. $\alpha$, which is in agreement with the statistics of uniform i.i.d. random points in the unit interval. In addition, we show that the same asymptotics holds almost surely in $\alpha \in \mathbb{R}$ when $L=O\left(N^{1\mathrm{/}2-\epsilon }\right)$. For slowly growing $L$, we further prove a central limit theorem for $S_N(L,\alpha )$ which holds for almost all $\alpha \in \mathbb{R}$.