Quasi-stationary description of fluctuations

A general method to evaluate fluctuations of the semiclassical one body Wigner function, in the framework of Landau's theory of quasi-stationary fluctuations, is presented. The model is valid far away from critical points, where the Boltzmann Nordheim Vlasov equation represents a good approximation of the average Wigner function. We discuss the different contributions of mean field fluctuations and fluctuations coming from the scattering processes, and apply the model to the evaluation of the damping of collective modes. The relaxation of giant resonances built on excited states is also discussed. (orig.)