Square roots and lattices

Abstract

We construct a point set in the Euclidean plane that elucidates the relationship between the fine-scale statistics of the fractional parts of $\sqrt{n}$ and directional statistics for a shifted lattice. We show that the randomly rotated, and then stretched, point set converges in distribution to a lattice-like random point process. This follows closely the arguments in Elkies and McMullen's original analysis for the gap statistics of $\sqrt{n}$ mod 1 in terms of random affine lattices [Duke Math. J. 123 (2004), 95-139]. There is, however, a curious subtlety: the limit process emerging in our construction is NOT invariant under the standard $\mathrm{SL}(2,\mathbb{R})$-action on ${\mathbb{R}}^2$.

10 pages; 4 figures; to appear in L'Enseignement Mathématique