EMERGENCE OF A WIENER PROCESS AS A RESULT OF THE QUANTUM-MECHANICAL INTERACTION WITH A MACROSCOPIC MEDIUM

We analyze a modified version of the Coleman-Hepp model, which is able to take into account energy-exchange processes between the incoming p article and the linear array made up of N spin-1/2 systems. We bring t o light the presence of a Wiener dissipative process in the weak-coupl ing, macroscopic (N --> infinity) limit. In such a limit and a restric ted portion of the total Hilbert space, the particle undergoes a sort of Brownian motion, while the flee Hamiltonian of the spin array serve s as a Wiener process. No partial trace is computed over the states of the spin system (which plays the role of ''reservoir''). The mechanis m of appearance of the stochastic process is discussed and contrasted to other noteworthy examples in the literature. The links with van Hov e's ''lambda(2)T'' limits are emphasized.