EXACT DERIVATION OF THE LANGEVIN AND MASTER-EQUATIONS FOR HARMONIC QUANTUM BROWNIAN-MOTION

A many-particle Hamiltonian, where the interaction term conserves the number of particles, is considered. A master equation for the populati ons of the different levels is derived in an exact way. It results in a local equation with time-dependent coefficients, which can be identi fied with the transition probabilities in the golden rule approximatio n. A reinterpretation of the model as a set of coupled harmonic oscill ators enables one to obtain for one of them an exact local Langevin eq uation, with time-dependent coefficients. (C) 1998 Elsevier Science B. V. All rights reserved.