Freiburg 1999 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 40: Theorie V

HK 40.2: Talk

Wednesday, March 24, 1999, 15:45–16:00, A

Stochastic interpretation of Kadanoff-Baym equations — •Carsten Greiner and Stefan Leupold — Institut für Theoretische Physik, Universität Giessen

We show that the nonperturbative transport equations, the so called ‘Kadanoff-Baym equations’, within the (non-)equilibrium real time Green’s function description can be be understood as the ensemble average over stochastic equations of Langevin type. The inherent presence of noise and dissipation related by the fluctuation-dissipation theorem guarantees that the modes or particles become thermally populated on average in the long-time limit. Our interpretation leads to a more intuitive physical picture of the process of thermalization and of the interpretation of the Kadanoff-Baym equations. One also immediately understands that the emerging wave equations for long wavelength modes with momenta |k|≪ T behave nearly as classical fields. We also demonstrate how the problem of so called ill-defined pinch singularities arising in a strictly perturbative expansion in out of equilibrium quantum field theory is resolved by a clear physical necessity of damping within the one-particle propagator. As possible applications we mention the nonequilibrium description of so called disoriented chiral condensates and also the dilepton production of vector meson decays in out of equilibrium situations in relativistic heavy ion collisions.