Heavy-ion collisions and the density dependence of the local mean field

We study the effect of the density dependence of the scalar and the vector part of the nucleonic self-energy in relativistic quantum molecular dynamics (RQMD) on observables like the transversal flow and the rapidity distribution. Linear and non-linear density dependences of the mean field are studied. The latter case can either be restricted to the scalar part of the mean field or be taken into account in both the scalar and vector parts. The mean field is determined from a non-linear extension of the Walecka model or from the Brueckner-Hartree-Fock G-matrix with the Reid soft-core potential. The transversal flow is very sensitive to these different approaches. In particular, a linear scaling of the flow with the effective mass of the considered models is observed. For the reaction Ar + KC1 at 1.8 GeV/nucleon a comparison with the data is given.