Active phase for activated random walks on the lattice in all dimensions

We show that the critical density of the Activated Random Walk model on Z(d) is strictly less than one when the sleep rate lambda is small enough, and tends to 0 when lambda -> 0, in any dimension d > 1. As far as we know, the result is new for d = 2. We prove this by showing that, for high enough density and small enough sleep rate, the stabilization time of the model on the ddimensional torus is exponentially large. To do so, we fix the the set of sites where the particles eventually fall asleep, which reduces the problem to a simpler model with density one. Taking advantage of the Abelian property of the model, we show that the stabilization time stochastically dominates the escape time of a one-dimensional random walk with a negative drift. We then check that this slow phase for the finite volume dynamics implies the existence of an active phase on the infinite lattice.