Atypical behaviors of a tagged particle in asymmetric simple exclusion

Sunder Sethuraman, S. R. S. Varadhan

Published 2023-11-13Version 1

Consider the asymmetric nearest-neighbor exclusion process (ASEP) on ${\mathbb Z}$ with single particle drift $\gamma>0$, starting from a Bernoulli product invariant measure $\nu_\rho$ with density $\rho$. It is known that the position $X_{N}$ of a tagged particle, say initially at the origin, at time $N$ satisfies an a.s. law of large numbers $\frac{1}{N}X_N \rightarrow \gamma(1-\rho)$ as $N\uparrow\infty$. In this context, we study the `typical' behavior of the tagged particle and `bulk' density evolution subject to `atypical' events $\{X_N\geq AN\}$ or $\{X_N\leq AN\}$ for $A\neq \gamma(1-\rho)$. We detail different structures, depending on whether $A<0$, $0\leq A< \gamma(1-\rho)$, $\gamma(1-\rho)<A< \gamma$, or $A\geq \gamma$, under which these atypical events are achieved, and compute associated large deviation costs. Among our results is an `upper tail' large deviation principle in scale $N$ for $\frac{1}{N}X_N$.