Quantum decoherence, entropy and thermalization in strong interactions at high energy. (I). Noisy and dissipative vacuum effects in toy models Original Research Article

Entropy is generated in high-multiplicity events by a dynamical separation of strongly interacting systems into partons and unobservable environment modes (almost constant field configurations) due to confinement. The effect is demonstrated in a non-relativistic single-particle model and a scalar field theory, where it amounts to quantum field Brownian motion. We analyze the quantum decoherence of partons, which formally corresponds to non-unitary time-evolution and causes entropy production, in terms of Schmidt and pointer states in the non-relativistic case. For the coupled scalar fields (partons and environment) we derive the Cornwall-Jackiw-Tomboulis effective action and equations of motion with the non-perturbative time-dependent variational method in TDHF approximation (to study the time-evolution of model structure functions in the sequel). We obtain a model-independent lower bound for the entropy in terms of two-point Wightman functions.