Equilibrium behavior in a nonequilibrium system: Ising-doped voter model on complete graph.

Abstract

While the Ising model belongs to the realm of equilibrium statistical mechanics, the voter model is an example of a nonequilibrium system. We examine an opinion formation model, which is a mixture of Ising and voter agents with concentrations p and 1-p, respectively. Although in our model for p<1 a detailed balance is violated, on a complete graph the average magnetization in the stationary state for any p>0 is shown to satisfy the same equation as for the pure Ising model (p=1). Numerical simulations confirm such a behavior. Variance of magnetization and susceptibility in our model increase for decreasing p and diverge at the temperature at which magnetization vanishes. Simulations on a random graph also show that a small concentration of Ising agents is sufficient to induce a ferromagnetic ordering.