  In the context of the search for the QCD critical point using non-Gaussian
fluctuations, we obtain the evolution equations for non-Gaussian cumulants to
the leading order of the systematic expansion in the magnitude of thermal
fluctuations. We develop a diagrammatic technique in which the leading order
contributions are given by tree diagrams. We introduce a Wigner transform for
multipoint correlators and derive the evolution equations for three- and
four-point Wigner functions for the problem of nonlinear stochastic diffusion
with multiplicative noise.
