Consequences of kinetic non-equilibrium for the nuclear equation-of-state in heavy ion collision

Highly compressed nuclear matter created in relativistic heavy collisions is to large extent governed by local non-equilibrium. As an idealized scenario colliding nuclear matter configurations are studied within both, relativistic mean field theory and using more realistic in-medium interactions based on the Dirac-Brueckner T-matrix. The equation of state in anisotropic matter is thereby governed by two competing effects: The enlarged phase space volume in colliding matter tends to soften the internal potential energy of the subsystems whereas the relative motion of the two currents leads to a strong additional repulsion in the system. An effective EOS constructed for anisotropic momentum configurations shows a significant net softening compared to ground state nuclear matter. This effect is found to be to large extend independent on the particular choice of the nuclear interaction. A critical discussion of standard transport approaches with respect to the considered non-equilibrium effects is given.