Differing averaged and quenched large deviations for random walks in random environments in dimensions two and three

TL;DR

This paper investigates the differences between quenched and averaged large deviation rate functions for random walks in random environments across various dimensions, revealing dimension-dependent behaviors and new distinctions.

Contribution

It establishes new results on when quenched and averaged large deviation rate functions are equal or differ, especially in low dimensions, contrasting with higher-dimensional cases.

Findings

In space-time RWRE, $I_q$ and $I_a$ are equal only at the typical velocity in 1+1 dimensions.

In 2+1 dimensions, $I_a$ is strictly less than $I_q$ near the typical velocity.

In space-only RWRE, $I_q$ and $I_a$ are not equal on any open set containing the typical velocity for certain non-nestling walks.

Abstract

We consider the quenched and the averaged (or annealed) large deviation rate functions $I_q$ and $I_a$ for space-time and (the usual) space-only RWRE on $\mathbb{Z}^d$. By Jensen's inequality, $I_a\leq I_q$. In the space-time case, when $d\geq3+1$, $I_q$ and $I_a$ are known to be equal on an open set containing the typical velocity $\xi_o$. When $d=1+1$, we prove that $I_q$ and $I_a$ are equal only at $\xi_o$. Similarly, when d=2+1, we show that $I_a<I_q$ on a punctured neighborhood of $\xi_o$. In the space-only case, we provide a class of non-nestling walks on $\mathbb{Z}^d$ with d=2 or 3, and prove that $I_q$ and $I_a$ are not identically equal on any open set containing $\xi_o$ whenever the walk is in that class. This is very different from the known results for non-nestling walks on $\mathbb{Z}^d$ with $d\geq4$.