Limiting distributions for RWCRE in the sub-ballistic regime and in the critical Gaussian regime

Abstract

Random Walks in Cooling Random Environments (RWCRE) is a model of random walks in dynamic random environments where the environment is frozen between a fixed sequence of times (called the cooling map) where it is resampled. Naturally the limiting distributions for this model depend both on the structure of the cooling sequence and on distribution $μ$ from which the environments are sampled. Previous results have considered the cases where $μ$ is such that the corresponding model of random walks in a fixed random environment (RWRE) is either (1) recurrent, (2) has a Gaussian limit with diffusive scaling (the $κ> 2$ case), or (3) has positive speed and a stable, non-Gaussian limit (the $κ\in (1,2)$ case). In this paper we examine the limiting distributions in two other transient regimes: the sub-ballistic, non-stable regime (i.e., $κ\in (0,1)$), and the Gaussian regime with non-diffusive scaling (i.e., $κ= 2$). In the first case we show that the limiting distributions are either Gaussian or a mixture of Gaussian and independent sums of Mittag-Leffler random variables, while in the second case the limiting distributions are always Gaussian but with a scaling that differs from the standard deviation by factor (which can oscillate, but which remains confined to some interval $[β,1]$) that depends very delicately on the properties of the cooling map.