Monte Carlo Simulation of Universal Short-Time Behavior in Critical Relaxation

The time evolution of the three-dimensional critical Ising model relaxing from a nonequilibrium initial state is studied by means of Monte Carlo simulation. We observe the characteristic initial increase of the (spatially) averaged magnetization predicted by Janssen et al. The exponent theta' that governs the initial behavior is determined, and the dependence of the long-time linear decay on the initial magnetization analyzed. Our simulation corroborates earlier results derived from continuum models.