Approach to Hyperuniformity in the One-Dimensional Facilitated Exclusion Process
S. Goldstein, J. L. Lebowitz, E. R. Speer
TL;DR
This work analyzes fluctuations in the one-dimensional Facilitated Exclusion Process at densities approaching the freezing threshold ρ_c = 1/2. It characterizes the infinite-time limiting measure ν_ρ and reveals a renewal-structure that governs interval-occupancy variances, yielding distinct scaling regimes for the variance V_ρ(L) depending on parity of L and on δ = 1/2 − ρ. The main result proves three regimes: a small-L constant behavior, an intermediate L^{3/2} growth, and a large-L linear growth matching ρ(1−ρ)L, with a hyperuniform behavior at ρ = 1/2 for odd L. The analysis hinges on the renewal process with long-tailed gaps described by Catalan-number statistics and a careful δ → 0 limit, linking to higher-dimensional observations and broader hyperuniformity phenomena.
Abstract
For the one-dimensional Facilitated Exclusion Process with initial state a product measure of density $ρ=1/2-δ$, $δ\ge0$, there exists an infinite-time limiting state $ν_ρ$ in which all particles are isolated and hence cannot move. We study the variance $V(L)$, under $ν_ρ$, of the number of particles in an interval of $L$ sites. Under $ν_{1/2}$ either all odd or all even sites are occupied, so that $V(L)=0$ for $L$ even and $V(L)=1/4$ for $L$ odd: the state is hyperuniform, since $V(L)$ grows more slowly than $L$. We prove that for densities approaching 1/2 from below there exist three regimes in $L$, in which the variance grows at different rates: for $L\ggδ^{-2}$, $V(L)\simeqρ(1-ρ)L$, just as in the initial state; for $A(δ)\ll L\llδ^{-2}$, with $A(δ)=δ^{-2/3}$ for $L$ odd and $A(δ)=1$ for $L$ even, $V(L)\simeq CL^{3/2}$ with $C=2\sqrt{2/π}/3$; and for $L\llδ^{-2/3}$ with $L$ odd, $V(L)\simeq1/4$. The analysis is based on a careful study of a renewal process with a long tail. Our study is motivated by simulation results showing similar behavior in higher dimensions; we discuss this background briefly.