Abstract
A new approach is proposed to derive a stochastic differential equation from a master equation. Starting from the Liouvillian in a Fock space formulation and using a functional integral representation in terms of coherent states the authors get the corresponding Langevin equation. As examples aggregation and segregation processes with different probability rates are analyzed. In the case of a state dependent growth rate it results in a generalized Kardar-Zhang equation including the kind of noise which is a purely Gaussian one in this model.