Nonequilibrium Dynamics of Scalar Fields in a Thermal Bath

Abstract

We study the approach to equilibrium for a scalar field which is coupled to a large thermal bath. Our analysis of the initial value problem is based on Kadanoff-Baym equations which are shown to be equivalent to a stochastic Langevin equation. The interaction with the thermal bath generates a temperature-dependent spectral density, either through decay and inverse decay processes or via Landau damping. In equilibrium, energy density and pressure are determined by the Bose-Einstein distribution function evaluated at a complex quasi-particle pole. The time evolution of the statistical propagator is compared with solutions of the Boltzmann equations for particles as well as quasi-particles. The dependence on initial conditions and the range of validity of the Boltzmann approximation are determined.

37 pages, 14 figures; references added

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• Leptogenesis
• The importance of flavor in leptogenesis
• Flavour Issues in Leptogenesis
• Non-thermal fixed points: effective weak-coupling for strongly correlated systems far from equilibrium
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