Universal power law tails of time correlation functions

The universal power law tails of single particle and multiparticle time correlation functions are derived from a unifying point of view, solely using the hydrodynamic modes of the system. The theory applies to general correlation functions and to systems more general than classical fluids. Moreover, it is argued that the collisional transfer part of the stress-stress correlation function in dense classical fluids has the same long-time tail similar to t(-1-d/2) as the velocity autocorrelation function in Lorentz gases.