GAUSSIAN WHITE-NOISE AS A MANY-PARTICLE PROCESS - THE KARDAR-PARISI-ZHANG EQUATION

A new approach is proposed to derive a stochastic differential equatio n from a Master equation. Starting from the Liouvillian in a Fock spac e formulation and using a functional integral representation in terms of coherent states we get the corresponding Langevin equation. As exam ples aggregation and segregation processes with different probability rates are analysed. In the case of a state dependent growth rate it re sults in a generalized Kardar-Parisi-Zhang equation 7! including the kind of noise which is a purely Gaussian one in this model.