DAMAGE SPREADING IN RANDOM-FIELD SYSTEMS

We investigate how a quenched random field influences the damage-sprea ding transition in kinetic Ising models. To this end we generalize a r ecent master equation approach and derive an effective field theory fo r damage spreading in random-held systems. This theory is applied to t he Glauber Ising model with a bimodal random-field distribution. We fi nd that the random field influences the spreading transition by two di fferent mechanisms with opposite effects. First, the random field favo urs the same particular direction of the spin variable at each site in both systems which reduces the damage. Second, the random held suppre sses the magnetization which in turn tends to increase the damage. The competition between these two effects leads to a rich behaviour.