DISSIPATIVE BEHAVIOR OF A QUANTUM SYSTEM INTERACTING WITH A MACROSCOPIC MEDIUM

The modified Coleman-Hepp (AgBr) model describes the interaction betwe en an ultrarelativistic quantum mechanical particle Q and an N-spin ar ray D (a macroscopic medium in the N --> infinity limit). We prove tha t the energy operator for D essentially behaves as a Wiener process in the weak-coupling, macroscopic limit, in a restricted state space. No assumptions are made on the spectrum of the Hamiltonian of the macros copic system D. The mechanism of appearance of such a stochastic proce ss and its relevance to issues like dissipation and irreversibility ar e briefly discussed.