"Going beyond perturbation theory in reaction-diffusion problems"
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The simplest reaction-diffusion problems are considered. They
consist on particles of a single species A that can
 diffuse with diffusion constant D and that can perform annihilation
(2A->nothing) or branching (A->2A) or, alternatively,
A->3A. It is shown that mean field methods and perturbative expansions
around it completely miss some simple
 properties as the structure of the phase diagram as found by Monte
Carlo simulations. It is shown that methods that go
beyond perturbation theory allows to quantitatively reproduce Monte
Carlo results in a very simple way.