Contact processes with quenched disorder on Zᵈ and on Erdos-Renyi graphs

In real systems impurities and defects play an important role in determining their properties. Here we will consider what probabilists have called the contact process in a random environment and what physicists have more precisely named the contact process with quenched disorder. We will concentrate our efforts on the special case called the random dilution model, in which sites independently and with probability p are active and particles on them give birth at rate λ, while the other sites are inert and particles on them do not give birth. We show that the resulting inhomogeniety can make dramatic changes in the behavior in the supercritical, subcritical, and critical behavior. In particular, the usual exponential decay of the desnity of particles in the subcritical phase becomes a power law (the Griffiths phase), and polynomial decay at the critical value becomes a power of log.