Simple theories of prethermalization

Prethermalization has emerged as an important and useful concept in modern quantum theory. It describes the situation where a system does not quickly settle down to equilibrium. Instead it settles to a long-lived, transient, temporary state that it will leave, eventually. Though somewhat inaccurate, one can compare this to a supercooled liquid that can dwell for a long time in the liquid phase, until it eventually freezes. The comparison is however not accurate in the following respect: the supercooled liquid will freeze (thermalize) quickly once it is made to realize that it should freeze. In contrast, the prethermalized system is just thermalizing slowly, so that other processes can develop meanwhile, and 'prethermalization' is the prominent one among those 'other processes'. The phenomenon has come to the center of attention because recent experiments with synthetic quantum matter allow to study such processes in great detail, and in isolation from outside disturbances. This motives and spurs the theory. The present project tries to formulate a simple, practical, and quantitative theory of prethermalization.