Coherent noise, scale invariance and intermittency in large systems
  We introduce a new class of models in which a large number of "agents" organize under the influence of an externally imposed coherent noise. The model shows reorganization events whose size distribution closely follows a power law over many decades, even in the case where the agents do not interact with each other. In addition the system displays "aftershock" events in which large disturbances are followed by a string of others at times which are distributed according to a 1/t law. We also find that the lifetimes of the agents in the system possess a power-law distribution. We explain all of these results using an approximate analytic treatment of the dynamics and discuss a number of variations on the basic model relevant to the study of particular physical systems. 
Kim Sneppen (Nordita) and M. E. J. Newman (Santa Fe Institute)