Density dependent hadron field theory.

In symmetric nuclear matter and stable nuclei one uses very often strictly phenomenological approaches, both in non-relativistic and relativistic formulation. In this contribution, a fully microscopic approach to nucleon-nucleon (NN) interactions in symmetric and asymmetric nuclear matter and extensions to hypernuclear matter will be discussed. Dirac-Brueckner theory is used to derive inmedium interactions [1] from well established free-space NN meson exchange potentials. By means of the Density Dependent Relativistic Hadron (DDRH) field theory [2, 3] the nuclear matter results for the in-medium interactions are used in a theoretically well defined approach in calculations for infinite nuclear matter, neutron stars and ground states of finite nuclei [3, 4] and hypernuclei [5]. In DDRH field theory interactions of baryons in a nuclear environment are described by density dependent meson-baryon vertices. They are introduced as functionals depending on Lorentz-scalars of the baryon field operators. In this way correlations and many-body effects are taken into account in an elegant and transparent formulation [3] by a Lagrangian L = LB +LM +Lint with baryonic (LB), mesonic (LM ) and interaction (Lint) parts which for nonstrange systems is: