On the number of gaps of sequences with Poissonian Pair Correlations

Abstract: A sequence $(x_n)$ on the torus is said to have Poissonian pair correlations if $# {1\le i\neq j\le N: |x_i-x_j| \le s/N}=2sN(1+o(1))$ for all reals $s>0$, as $N\to \infty$. It is known that, if $(x_n)$ has Poissonian pair correlations, then the number $g(n)$ of different gap lengths between neighboring elements of ${x_1,\ldots,x_n}$ cannot be bounded along every index subsequence $(n_t)$. First, we improve this by showing that the maximum among the multiplicities of the neighboring gap lengths of ${x_1,\ldots,x_n}$ is $o(n)$, as $n\to \infty$. Furthermore, we show that, for every function $f: \mathbf{N}^+\to \mathbf{N}^+$ with $\lim_n f(n)=\infty$, there exists a sequence $(x_n)$ with Poissonian pair correlations and such that $g(n) \le f(n)$ for all sufficiently large $n$. This answers negatively a question posed by G. Larcher.