Explosive Percolation is Continuous, but with Unusual Finite Size Behavior

We study four Achlioptas-type processes with "explosive" percolation transitions. All transitions are clearly continuous, but their finite size scaling functions are not entirely holomorphic. The distributions of the order parameter, i.e., the relative size s(max)/N of the largest cluster, are double humped. But-in contrast to first-order phase transitions-the distance between the two peaks decreases with system size N as N-eta with eta > 0. We find different positive values of beta (defined via < s(max)/N > similar to (p - p(c))(beta) for infinite systems) for each model, showing that they are all in different universality classes. In contrast, the exponent Theta (defined such that observables are homogeneous functions of (p - p(c))N-Theta) is close to-or even equal to-1/2 for all models.