Timing and shape of stochastic autocatalytic burst formation.

Chemical, physical, and ecological systems passing through a saddle-node bifurcation will, momentarily, find themselves balanced at a semistable steady state. If perturbed by noise, such systems will escape from the zero-steady state, with escape time sensitive to noise. When the model is extended to include space, this leads to different points in space "escaping from zero" at different times, and uniform initial conditions nucleate into sharp peaks spreading randomly across a nearly uniform background, a phenomenon closely resembling nucleation during phase transition. We use Large Deviation Theory to determine burst shape and temporal scaling with respect to noise amplitude. These results give a prototype for a particular form of patternless symmetry breaking in the vicinity of a stability boundary and demonstrate how microscopic noise can lead to macroscopic effects in such a region.