Nonequilibrium quantum-field dynamics and off-shell transport for image-theory in image dimensions Original Research Article

We solve the Kadanoff–Baym equations for nonequilibrium initial configurations of the ϕ4-theory in 2+1 dimensions and compare to explicit solutions of generalized transport equations for the same theory. The latter transport equations are derived from the Kadanoff–Baym equation in a first order gradient expansion in phase-space and explicitly retain the off-shell dynamics as inherent in the time-dependent spectral functions. The solutions of these equations compare very well with the exact solutions of the full Kadanoff–Baym equations with respect to the occupation numbers of the individual modes, the spectral evolution as well as the chemical equilibration process. Furthermore, the proper equilibrium off-shell distribution is reached for large times contrary to the quasiparticle Boltzmann limit. We additionally present a direct comparison of the solution of the generalized transport equations in the Kadanoff–Baym and Botermans–Malfliet form; both solutions are found to agree very well with each other.