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# Séminaire

## Macroscopic fluctuations in non-equilibrium systems

Many natural systems are maintained in a stationary state through continuous exchange of matter, energy or information with their surroundings. These various currents break time-reversal

by generating a continuous increase of entropy. The behaviour of such non-equilibrium systems can not be accounted for by the Principles of Thermodynamics or by the Gibbs-Boltzmann laws of statistical physics. Although linear response theory and the Onsager-Machlup functional provide useful descriptions of large scale fluctuations in driven systems, they are only valid, at first order, in the vicinity of equilibrium.

In the last two decades, important advances in our understanding of processes far from equilibrium

have been achieved, for which rare events, large deviations and ﬂuctuations relations provide a

uniﬁed framework. The emergence of universal features can be studied thanks to a variational

principle, proposed by G. Jona-Lasinio and his collaborators, known as the Macroscopic Fluctu-

ation Theory (MFT). In this theory, optimal ﬂuctuations far from equilibrium are determined at

a coarse-grained scale by two coupled non-linear hydrodynamic equations. The objective of this

talk is to present these concepts and to illustrate them with some exact solutions of the MFT

equations.

### Orateur(s)

**Kirone Mallick**

IPhT, CEA Saclay

### Organisateur(s)

*PCC Seminar Team*

### Invité(e)(s) par

**Nolan Burban**