Large deviations for random walk in a space--time product environment

We consider random walk $(X_n)_{n\geq0}$ on $\mathbb{Z}^d$ in a space--time product environment $ω\inΩ$. We take the point of view of the particle and focus on the environment Markov chain $(T_{n,X_n}ω)_{n\geq0}$ where $T$ denotes the shift on $Ω$. Conditioned on the particle having asymptotic mean velocity equal to any given $ξ$, we show that the empirical process of the environment Markov chain converges to a stationary process $μ_ξ^{\infty}$ under the averaged measure. When $d\geq3$ and $ξ$ is sufficiently close to the typical velocity, we prove that averaged and quenched large deviations are equivalent and when conditioned on the particle having asymptotic mean velocity $ξ$, the empirical process of the environment Markov chain converges to $μ_ξ^{\infty}$ under the quenched measure as well. In this case, we show that $μ_ξ^{\infty}$ is a stationary Markov process whose kernel is obtained from the original kernel by a Doob $h$-transform.

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