Noise-induced bound states

We investigate the presence of two-particle bound states in the stochastic dynamics generator of weakly coupled Ginzburg-Landau models, and study thei r dependence on the noise strength. For the space dimension d less than or equal to 3, by analyzing the Bethe-Salpeter equation in the ladder approxim ation, we show that a bound state appears but disappears again at a higher value of the noise intensity. Furthermore, we show that in the case of the polynomial interaction with a negative quartic term the bound state appears and disappears for the noise intensity much smaller than that for the inte raction with the quartic term positive. We also describe the curves giving the bound states masses in terms of the noise strength, which show the effe ct that, for a suitable noise intensity, the two-particle bound state mass becomes smaller than the one-particle mass. (C) 2001 Published by Elsevier Science B.V.