SELF-ORGANIZED CRITICALITY AS AN ABSORBING-STATE PHASE-TRANSITION

We explore the connection between self-organized criticality and phase transitions in models with absorbing states. sandpile models are foun d to exhibit criticality only when a pair of relevant parameters - dis sipation epsilon and driving field h - are set to their critical value s. The critical values of epsilon and h are both equal to zero. The fi rst result is due to the absence of saturation (no bound on energy) in the sandpile model, while the second result is common to other absorb ing-state transitions. The original definition of the sandpile model p laces it at the point (epsilon = 0,h = 0(+)): it is critical by defini tion. We argue power-law avalanche distributions are a general feature of models with infinitely many absorbing configurations, when they ar e subject to slow driving at the critical point. Our assertions are su pported by simulations of the sandpile at epsilon=h=0 and fixed energy density zeta (no drive, periodic boundaries), and of the slowly drive n pair contact process. We formulate a held theory for the sandpile mo del, in which the order parameter is coupled to a conserved energy den sity, which plays the role of an effective creation rate.