Covariant Boltzmann-Uehling-Uhlenbeck approach for heavy-ion collisions

We present a covariant transport theory for heavy-ion collisions based on the σ-ω model. The two-body collision term is introduced in line with relativistic classical kinetic theory assuming the free nucleon-nucleon cross section in the collision integral. Within this approach, we study collisions of ${}_{}{}^{16}{}_{}{}^{}$O${+}^{16}$O at 600 MeV/nucleon for two different parameter sets of the underlying Lagrangian density, i.e., different equations of state. The most striking result is the strong sensitivity of the transverse momentum distribution on the momentum dependence of the mean field which is self-consistently included in the relativistic approach. We find that residual two-particle collisions might even slightly reduce the transverse momentum $p_t$ due to an increase of stopping power obtained from the collisions. An increase of the cross section by a factor of 2 leads to a much smaller enhancement of $p_t$ than observed in nonrelativistic calculations with a momentum independent mean field. We furthermore present a first application to high-energy photon production and study the influence of the equation of state on the differential photon yield.