The relativistic BUU approach analysis of retardation effects and thermal properties

The study of the nuclear equation of state (EOS) is one of the major goals in high energy heavy-ion collisions. However, it has turned out that the extraction of reliable information about the EOS is a nontrivial task. Theoretical investigations, like simulations of the Boltzmann-Uehling-Uhlenbect (BUU) equation have to include the momentum dependence of the mean-field potential and should also study the sensitivity of the observables on medium modifications of the nucleon-nucleon cross section. Therefore, at bombarding energies in the order of 1 GeV/nucleon an relativistic treatment, which consistently includes these features, is necessary. In this spirit, a relativistic transport approach has been proposed and investigated. Together with a relativistic generalization of the BUU transport equation one obtains equations of motion for the meson-fields which mediate the interaction. In this paper, the authors present results which include the full solution of these field-equations and compare to field theory proposed by. The numerical analysis shows that an explicit propagation of the mesons leads to negligible modifications of the time-evolution of the baryonic phase-space distribution up to at least several GeV per nucleon bombarding energy for heavy-ion collisions. How much this result is altered by the inclusion of the collision-term will be studied in the future