Nonequilibrium Dynamics and Off-Shell Transport of Relativistic Quantum Fields

S. Juchem, W. Cassing, C. Greiner University of Giessen, 2 University of Frankfurt The dynamics of quantum many-body systems are a challenging task for far-from-equilibrium conditions as appearing in high energy heavy-ion collisions or cosmological problems. It is of fundamental importance to describe abinitio thermalization by taking into account all quantum aspects of the particles (or fields) rather than invoking semi-classical approximation schemes – as inherent in the Boltzmann limit – from the beginning [1, 2] and to develop tractable approximation schemes that retain the essential quantum dynamics. We here consider the equilibration of the scalar φtheory in 2+1 space-time dimensions. The evolution equations for the Green function iG(x, y) =< φ(y)φ(x) > are derived self-consistently by a loop expansion of the two-particle irreducible (2PI) action [3]. When considering contributions up to the three-loop order one obtains a Kadanoff-Baym equation incorporating two types of selfenergies: a) the tadpole diagram that produces a mean field while b) the sunset diagram contains the influence of scattering processes and leads to a non-locality in time (memory integrals). We recall that equilibration requires the inclusion of collisions as inherent in the sunset diagram [2]. Due to the numerical expense we here restrict to homogeneous systems in space and solve the Kadanoff-Baym (KB) equations in momentum space.