Abstract:
The classical work by Onsager and Machlup (1953) describes the dynamics of small fluctuations in a process of relaxation to equilibrium. Recently there have been fast progress in extending this approach in various directions, both for macroscopic and mesoscopic systems. After a short review, I will concentrate on the generic structure of steady dynamical fluctuations in open systems with a small number of degrees of freedom, which is not restricted to close to equilibrium or to weak noise. We identify a natural collection of fluctuation observables and give an explicit formula for the large time asymptotics of the probability of fluctuations. The emergence and the limitation of certain familiar variational principles becomes understood from the decoupling between the time-symmetric and time-antisymmetric sectors when close to equilibrium. For systems subject to non-Gaussian noise, a new observable is recognized to play an important role.

[1] C. Maes and K. Netocny, Europhys. Lett. 82 (2008) 30003.
[2] C. Maes, K. Netocny, and B. Wynants, Physica A 387 (2008) 2675.
[3] C. Maes, K. Netocny, and B. Wynants, arXiv:cond-mat/0709.4327.