20 research outputs found

    The Boltzmann Equation in Classical and Quantum Field Theory

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    Improving upon the previous treatment by Mueller and Son, we derive the Boltzmann equation that results from a classical scalar field theory. This is obtained by starting from the corresponding quantum field theory and taking the classical limit with particular emphasis on the path integral and perturbation theory. A previously overlooked Van-Vleck determinant is shown to control the tadpole type of self-energy that can still appear in the classical perturbation theory. Further comments on the validity of the approximations and possible applications are also given.Comment: 22 pages, 3 eps figures. Version to appear in Physical Review

    2PI nonequilibrium versus transport equations for an ultracold Bose gas

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    The far-from-equilibrium dynamics of an ultracold, one-dimensional Bose gas is studied. The focus is set on the comparison between the solutions of fully dynamical evolution equations derived from the 2PI effective action and their corresponding kinetic approximation in the form of Boltzmann-type transport equations. It is shown that during the time evolution of the gas a kinetic description which includes non-Markovian memory effects in a gradient expansion becomes valid. The time scale at which this occurs is shown to exceed significantly the time scale at which the system's evolution enters a near-equilibrium drift period where a fluctuation dissipation relation is found to hold and which would seem to be predestined for the kinetic approximation.Comment: 24 pages, 7 figures. References adde

    Pathophysiologie der neurogenen Blasendysfunktion

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