Fluctuations out of equilibrium.

A generalized fluctuation-dissipation theorem involving slowly varying parameters is presented. Application of the Langevin method, the method of moments and of a multiscale technique reveal that not only dissipation but also dispersive contributions determine the spectral functions of fluctuations in arbitrary statistical systems. The non-Joule dispersive contribution is characterized by a novel non-local effect due to the additional phase shift between the force and the response of the system. This phase shift occurs as a result of parametric control to the system. The general formalism is illustrated by concrete examples and applications.This article is part of the theme issue 'Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 2)'.