Noise-induced dynamical transition in systems with symmetric absorbing states

Model systems with absorbing states have featured prominently in the quest for a fundamental understanding of far-from-equilibrium phase transitions and critical phenomena. A clear picture of how systems with multiple absorbing states behave is still emerging. These include cases where several competing species can drive each other to extinction. The static phase diagram for systems with two symmetric absorbing states has recently been shown to have a much richer structure than those with a single absorbing state, featuring in particular order-disorder transitions of several different types. We have investigated the effect of noise strength on the macroscopic ordering dynamics of systems of this kind. Using an explicit stochastic microscopic model, we present evidence for a phase transition in the coarsening dynamics, from an Ising-like to a voter-like behaviour, as the noise strength is increased past a nontrivial critical value. By mapping to a thermal diffusion process, we argue that the transition arises due to locally-absorbing states being entered more readily in the high-noise regime, which in turn prevents surface tension from driving the ordering process.