Non-equilibrium Phase Transitions in Condensed Matter and Cosmology: Spinodal Decomposition, Condensates and Defects∗

These lectures address the dynamics of phase ordering out of equilibrium in condensed matter and in quantum field theory in cosmological settings, emphasizing their similarities and differences. In condensed matter we describe the phenomenological approach based on the Time Dependent GinzburgLandau (TDGL) description. After a general discussion of the main experimental and theoretical features of phase ordering kinetics and the description of linear (spinodal) instabilities we introduce the scaling hypothesis and show how a dynamical correlation length emerges in the large N limit in condensed matter systems. The large N approximation is a powerful tool in quantum field theory that allows the study of non-perturbative phenomena in a consistent manner. We study the exact solution to the dynamics after a quench in this limit in Minkowski space time and in radiation dominated Friedman-Robertson-Walker Cosmology. There are some remarkable similarities between these very different settings such as the emergence of a scaling regime and of a dynamical correlation length at late times that describe the formation and growth of ordered regions. In quantum field theory and cosmology this length scale is constrained by causality and its growth in time is also associated with coarsening and the onset of a condensate. We provide a density matrix interpretation of the formation of defects and the classicalization of quantum fluctuations. ∗Lectures delivered at the NATO Advanced Study Institute: Topological Defects and the Non-Equilibrium Dynamics of Symmetry Breaking Phase Transitions †Laboratoire Associé au CNRS UMR 7589.