Nonlinear dynamics of gross variables and the renormalization of transport coefficients

Abstract

The slowly decaying hydrodynamic modes in many-body systems are obtained from a theory which avoids perturbation methods. The theory is based on a projection-operator technique which is applied to quantities characterizing the state of the system at various levels of its description. The main result is that a true transport coefficient is shown to consist of two contributions (one which decays rapidly in time and another one which decays slowly), is non-Markoffian, and arises from the nonlinear interactions among the collective modes. This contribution is obtained in a closed analytical form which is further analyzed within the context of our present-day information derived from computer and laboratory experiments. The relationship between this work and similar earlier work on this problem is also discussed.