Why this conference?

Eighty years ago Lars Onsager published two fundamental papers on irreversible processes. There, he generalised a number of previous observations and conjectures (e.g. Thomson thermoelectric theory or Helmoltz's theory of liquid junctions), connecting - for the first time in a universal way - relaxations and fluctuations in mesoscopic processes.
The importance of Onsager's contribution was to recognize time-reversal symmetry as sufficient to establish reciprocal relations between transport coefficients, as well as a variational principle guiding the dynamics of fluctuations. A key passage was postulating that time-correlations obey the same equations of corresponding macro-variables. For instance, time-correlations of local temperature fluctuations satisfy the Fourier's law.

In successive years and in several different contexts, Onsager's theory was put in contact with the theory of fluctuations - originated by Einstein's work on Brownian motion - and with linear response theory, leading to the Fluctuation-Dissipation relation and to the Green-Kubo formula for transport coefficients, which both have a great value for applications as well as a deep fundamental meaning.
In Onsager's and Kubo's theories, all relations remain "simple" provided that some kind of time-reversal symmetry holds. As soon as such a symmetry is lost, simplicity of linear response and transport coefficients is no more guaranteed. Time-reversal symmetry is broken in widespread natural phenomena: a constraint against equilibration is usually given by non-equilibrium boundary conditions. If such boundaries are constant (or - better - their unavoidable relaxation occurs on much larger timescales), one speaks of a non-equilibrium stationary state (NESS). In other situations the constraint against equilibration is given by dynamics itself which becomes exceedingly slow, as in glassy systems. In all those cases response theory must be generalized, paying a price in simplicity.

In particular, equilibrium fluctuation dissipation relations (EFDR) predict linear response to be proportional to an equilibrium time-correlator involving the work done (or dissipated) by the applied perturbation. This thermal analogy, which makes EFDR easy to be applied, is lost when considering the perturbation of a system already far from equilibrium, e.g. in a NESS or during aging.

Several generalised relations (GFDR) have been recently proposed: they still connect the perturbed system to the unperturbed one, but require a detailed microscopic knowledge of the system. For such a reason they are less appealing than their equilibrium counterpart. Some GFDR may take a simple form in particular situations, e.g. an effective temperature may replace the thermostat temperature in a range of well separated timescales for aging glassy systems, but this scenario is far from being general. More frequently, one faces a situation where the EFDR is modified by additional contributions of more complex nature.

It is the purpose of this workshop to discuss all those recent ideas, comparing them and debating about the existence (or the reason of a lack) of an unifying principle for non-equilibrium fluctuation-response theory.

Main Topics:

* linear (and non-linear) response theory far from equilibrium
* FDR for stationary states and non-stationary (aging) relaxations
* FDR for hydrodynamics fluctuations
* applications of FDR (nanophysics, biophysics, granular materials)

There will be

* 16 plenary talks (45 minutes)
* 10 contributed talks (15 minutes)
* posters