Studies on the structure of nuclear systems are performed, which are based on realistic nucleon-nucleon interactions. Such realistic interactions induce two-body correlations in the nuclear many-body wave function. In particular one finds deviations of the single-particle Green's function from the mean field prediction of a Hartree-Fock theory. Such modifications give rise to a modification in the response function of the nuclear system. This response function characterizes the excitation modes of the nuclear system. It is also the most relevant ingredient for the study of the propagator of a meson in the nuclear medium. This meson propagators, on the other hand, ~are very important to study modifications of the nucleon nucleon force in the nuclear medium and thereby influence the self-consistent evaluation of the single-particle Green's function.
The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the Green's function in nuclear matter using realistic nucleon-nucleon interactions. The results are compared with recent experimental data derived from (e,e'p) reactions on 12C. A rather good agreement is obtained if the Green's functions are calculated in a non-perturbative way.
The self-energy of nucleons in asymmetric nuclear matter is evaluated employing different realistic models for the nucleon-nucleon interaction. Starting from the Brueckner-Hartree-Fock approximation without the usual angle-average in the two-nucleon propagator the effects of the hole-hole contributions are investigated within the self-consistent Green's function approach. Special attention is paid to the isospin-dependence of correlations, which can be deduced from the spectral functions of nucleons in asymmetric matter.