Criticality of a dissipative self-organizing process in a dynamic population

Abstract

We derive a general formulation of the self-organized branching process by considering sandpile dynamics in an evolving population characterized by "birth" (excitation) and "death" (de-excitation) of active sites ($z=1$). New active sites are born in empty sites ($z=0$) with a probability of $\eta$, whereas active sites die, thus becoming empty, with a probability $\lambda$. Subsequently, when an active site becomes unstable ($z=2$), it topples by transferring two grains to two randomly chosen sites with probability $\alpha$ or, by transferring only one grain to a randomly selected site (while retaining the other) with probability $\beta=1+\frac{\lambda}{\eta}-2\alpha$, thus remaining active after toppling. We show that when sandpile dynamics occurs in an evolving population, self-organized criticality, characterized by a power-law avalanche size distribution with exponent $\tau_s=3/2$ and power-law avalanche duration distribution with exponent $\tau_T=2$ at very high dimension $n >> 1$, is achieved even in the presence of dissipation ($\epsilon = 1-\alpha - \beta > 0$), contrary to previous claims.