The symmetry energy for nuclear matter and its relation to the neutron skin in finite nuclei is discussed. The symmetry energy as a function of density obtained in a self-consistent Green function approach is presented and compared to the results of other recent theoretical approaches. A partial explanation of the linear relation between the symmetry energy and the neutron skin is proposed. The potential of several experimental methods to extract the neutron skin is examined.

A fully self-consistent treatment of short-range correlations in nuclear matter is presented. Different implementations of the determination of the nucleon spectral functions for different interactions are shown to be consistent with each other. The resulting saturation densities are closer to the empirical result when compared with (continuous choice) Brueckner-Hartree-Fock values. Arguments for the dominance of short-range correlations in determining the nuclear-matter saturation density are presented. A further survey of the role of long-range correlations suggests that the inclusion of pionic contributions to ring diagrams in nuclear matter leads to higher saturation densities than empirically observed. A possible resolution of the nuclear-matter saturation problem is suggested. Several different remedies for this serious problem have been proposed over the years. The intrinsic structure of the nucleon and its related strong coupling to the ∆-isobar inevitably requires the consideration of three-body (or more-body) forces. When three-body forces are considered in variational calculations it is possible to achieve better saturation properties only when an adhoc repulsive short-range component of this three-body force is added [6,7]. It has also been suggested that a relativistic treatment of the nucleon in the medium using a DiracBrueckner approach provides the necessary ingredients for a better description of saturation [8,9,10,11].All many-body methods developed for nuclear matter have focused on a proper treatment of short-range correlations (SRC) without the benefit of experimental information on the influence of these correlations on the properties of the nucleon in the medium. This influence can now be clearly identified by considering recent results from (e,e ′ p) reactions [12,13,14] and theoretical calculations of the nucleon spectral function in nuclear matter [15,16,17]. A recent analysis of the (e,e ′ p) reaction on 208 Pb in a wide range of missing energies and for missing momenta below 270 MeV/c yields information on the occupation numbers of all the deeply-bound proton orbitals. These data indicate that all these orbitals are depleted by the same amount of about 15% [18]. These occupation numbers are associated with the orbits which yield an accurate fit to the (e,e ′ p) cross section. The properties of these occupation numbers suggest that the main effect of the global depletion of these meanfield orbitals is due to SRC. Indeed, the effect of the coupling of hole states to low-lying collective excitations only affects occupation numbers of states in the immediate vicinity of the Fermi energy [19]. In addition, nuclear matter momentum distributions display such an overall global depletion due to short-range and tensor correlations [17,20,21]. The latter results formed the basis of the now corroborated prediction [22,23] for the occupation numbers in 208 Pb [18].Most of this depleted single-particle (sp) strength is located at energies more than 100 MeV above the Fermi energy [17,20,22]. This ap...

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Long-range correlations, which are partially responsible for the observed fragmentation and depletion of low-lying single-particle strength, are studied in the Green's function formalism. The self-energy is expanded up to second order in the residual interaction. We compare two methods of implementing self-consistency in the solution of the Dyson equation beyond Hartree-Fock, for the case of the 16 O nucleus. It is found that the energy-bin method and the BAGEL method lead to globally equivalent results. In both methods the final single-particle strength functions are characterized by exponential tails at energies far from the Fermi level.