Higher-order hyperuniformity of random measures

Abstract

We study higher-order hyperuniformity through the large-scale variance of local $k$-point patterns, and write $\HU_k$ for the resulting condition; $\HU_1$ is ordinary hyperuniformity. The conditions $\HU_k$ need not coincide: for every $k\geq1$ there exists an $\mathbb R$-invariant weakly mixing simple point process that belongs to $\HU_j$ for all $j\leq k$ but not to $\HU_{k+1}$. Randomly translated lattices belong to $\HU_k$ for every $k$, whereas sufficiently small non-degenerate iid perturbations of lattices and projection determinantal point processes already belong to $\HU_1\setminus\HU_2$. For regular Euclidean cut-and-project processes we give an exact criterion for $\HU_k$. For ball windows, $\HU_k$ is equivalent to $\HU_1$ in internal dimensions two and three, whereas in every internal dimension $m\geq4$ we construct ball-window examples in $\HU_1\setminus\HU_2$. Finally, the nonperiodic Kurasov--Sarnak Fourier-quasicrystalline point process is stealthy---its first-order spectrum has a gap at the origin---yet does not belong to $\HU_2$.