Crossover from dynamical percolation class to directed percolation class on a two dimensional lattice

Abstract

We study the crossover phenomena from the dynamical percolation class (DyP) to the directed percolation class (DP) in the model of diseases spreading, Susceptible-Infected-Refractory-Susceptible (SIRS) on a two-dimensional lattice. In this model, agents of three species S, I, and R on a lattice react as follows: $S+I\rightarrow I+I$ with probability $\lambda$, $I\rightarrow R$ after infection time $\tau_I$ and $R\rightarrow I$ after recovery time $\tau_R$. Depending on the value of the parameter $\tau_R$, the SIRS model can be reduced to the following two well-known special cases. On the one hand, when $\tau_R \rightarrow 0$, the SIRS model reduces to the SIS model. On the other hand, when $\tau_R \rightarrow \infty$ the model reduces to SIR model. It is known that, whereas the SIS model belongs to the DP universality class, the SIR model belongs to the DyP universality class. We can deduce from the model dynamics that, SIRS will behave as an SIS model for any finite values of $\tau_R$. SIRS will behave as SIR only when $\tau_R=\infty$. Using Monte Carlo simulations we show that as far as the $\tau_R$ is finite the SIRS belongs to the DP university class. We also study the phase diagram and analyze the scaling behavior of this model along the critical line. By numerical simulation and analytical argument, we find that the crossover from DyP to DP is described by the crossover exponent $1/\phi=0.67(2)$.