Nucleon properties in the nuclear medium

Abstract

Recent developments in the many-body theory of interacting fermions are discussed employing a self-consistent Green function approach. This scheme is outlined and its application to nuclear systems is presented. Special attention is paid to the consistent inclusion of short-range and long-range correlations induced by realistic nucleonnucleon interactions. Such correlations lead to occupation probabilities which deviate from the simple mean-field or shell-model description. The scheme is extended to incorporate relativistic effects. Also applications of field theoretical models for hadrons in a nuclear medium and their relation to QCD are discussed. This review was received in February 1992. 0034-4885/92/111947+77% 30.00 @ 1992 IOP Publishing Ltd 1947 ments (de Witt Huberts 1990, Dieperink and de Witt Huberts 1990, Sick and de Witt perfected at the NiKHEF faciiiiy in rQmsieraam with high-resoiuiion {e, e'p] expei'l-W H Dickhoff and H Muther between two nucleons. A commonly adopted description mode for the interaction which includes the coupling to these excited states involves the exchange of the bosonic $-&:&on a;&?; !& :he two-pion continuum with scalar-isoscalar quantum numbers usually referred to as the o-meson. In more elaborate descriptions the coupled problem of nucleons and A'sprovides a very convenient and physically appealing description. A review of the meson-exchange description of the nuclear interaction has recently been given by interactions between qp electrons in a solid in terms of the exchange of the relevant bosonic excitation modes of the system, like lattice phonons which occur at low energy, or plasmons which occur at higher energy (but couple strongly).An important requirement imposed on these meson-exchange interactions is that when used in a scattering equation for two nucleons an accurate fit of the experimental data up to pion production threshold is obtained. Other more phenomenological interactions have been constructed which also yield an accurate description of twonucleon scattering and bound-state data. Such interactions together with the mesonexchange descriptions, are referred to as ree!istic interactions when they accurately describe all experimental data in the two-nucleon system up to 140 MeV excitation energy. A crucial ingredient in the description of these data is the presence of a mechanism which suppresses the probability of finding the two-nucleon state at short relative distance. In older descriptions this was accomplished by using a pnenomenological hard-core repulsion. In a meson-exchange picture this is accomplished by the exchange of the o-meson which leads to a strong repulsion at short distance. That the scattering data require this notion is hardy surprising, since when two nucieons are smashed together violently a wealth of excitations can be generated when the constituents of the nucleons come close together. It should therefore be no surprise that any mechanism which describes this suppression of the two-nucleon state at short range supplemented by the exchan...

Self-consistent Green's function method for nuclei and nuclear matter

“…4.6 for the fully self-consistent results. The latter results formed the basis of the now corroborated prediction [54,146,147] for the occupation numbers in 208 Pb [143].…”

“…Most of this depleted sp strength is located at energies more than 100 MeV above the Fermi energy [60,61,54]. This appearance of strength at high energy is another important aspect of the influence of short-range and tensor correlations.…”

“…Some of this work has been reviewed in Refs. [54,1]. The main emphasis in the present review is on the progress that has been made recently in implementing the self-consistency condition on the single-particle (sp) propagators in consort with the summation of ladder diagrams for the effective interaction.…”

Off-shell behavior of nucleon self-energy in asymmetric nuclear matter

“…As it does not account for hole-hole ladder terms one does not obtain a spectral distribution for energies ω < ε F . The depletion of the occupation numbers for the hole states (k < k F ), however, can be determined from the single-particle strength at the quasi particle poles of the single-particle Greens function [20] z(k) = 1 − ∂ℜeU (|k|, ω) ∂ω…”

Collective excitations and ground state correlations

“…This implies that the Lehmann representation of the single-particle Green function is not any longer given by only one pole but must be presented in the general form (see e.g. [6])…”