Recent results obtained by applying the method of self-consistent Green's functions to nuclei and nuclear matter are reviewed. Particular attention is given to the description of experimental data obtained from the (e,e ′ p) and (e,e ′ 2N) reactions that determine one and two-nucleon removal probabilities in nuclei since the corresponding amplitudes are directly related to the imaginary parts of the single-particle and two-particle propagators. For this reason and the fact that these amplitudes can now be calculated with the inclusion of all the relevant physical processes, it is useful to explore the efficacy of the method of self-consistent Green's functions in describing these experimental data. Results for both finite nuclei and nuclear matter are discussed with particular emphasis on clarifying the role of short-range correlations in determining various experimental quantities. The important role of long-range correlations in determining the structure of lowenergy correlations is also documented. For a complete understanding of nuclear phenomena it is therefore essential to include both types of physical correlations. We demonstrate that recent experimental results for these reactions combined with the reported theoretical calculations yield a very clear understanding of the properties of all protons in the nucleus. We propose that this knowledge of the properties of constituent fermions in a correlated many-body system is a unique feature of nuclear physics.

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Resolution of discrete final states in the16 O(e,e ′ pp) 14 C reaction may provide an interesting tool to discriminate between contributions from one-and two-body currents in this reaction. This is based on the observation that the 0 + ground state and first 2 + state of 14 C are reached predominantly by the removal of a 1 S0 pair from 16 O in this reaction, whereas other states mostly arise by the removal of a 3 P pair. This theoretical prediction has been supported recently by an analysis of the pair momentum distribution of the experimental data [1]. In this paper we present results of reaction calculations performed in a direct knock-out framework where final-state interaction and one-and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of 16 O and include both long-range and short-range correlations. The kinematics chosen in the calculations is relevant for recent experiments at NIKHEF and Mainz. We find that the knock-out of a 3 P proton pair is largely due to the (two-body) ∆-current. The 1 S0 pair knock-out, on the other hand, is dominated by contributions from the one-body current and therefore sensitive to two-body short-range correlations. This opens up good perspectives for the study of these correlations in the 16 O(e,e ′ pp) reaction involving the lowest few states in 14 C. In particular the longitudinal structure function f00, which might be separated with super-parallel kinematics, turns out to be quite sensitive to the NN potential that is adopted in the calculations.

The influence of short-range correlations on the momentum and energy distribution of nucleons in nuclei is evaluated assuming a realistic meson-exchange potential for the nucleon-nucleon interaction. Using the Green-function approach the calculations are performed directly for the finite nucleus 16 O avoiding the local density approximation and its reference to studies of infinite nuclear matter. The nucleon-nucleon correlations induced by the short-range and tensor components of the interaction yield an enhancement of the momentum distribution at high momenta as compared to the Hartree-Fock description. These high-momentum components should be observed mainly in nucleon knockout reactions like (e, e ′ p) leaving the final nucleus in a state of high excitation energy. Our analysis also demonstrates that non-negligible contributions to the momentum distribution should be found in partial waves which are unoccupied in the simple shell-model. The treatment of correlations beyond the Brueckner-Hartree-Fock approximation also yields an improvement for the calculated ground-state properties.

A comprehensive description of all single-particle properties associated with the nucleus 40 Ca is generated by employing a nonlocal dispersive optical potential capable of simultaneously reproducing all relevant data above and below the Fermi energy. The introduction of nonlocality in the absorptive potentials yields equivalent elastic differential cross sections as compared to local versions but changes the absorption profile as a function of angular momentum suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential to allow for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by (e, e ′ p) and (p, 2p) reactions are correctly incorporated, including the energy distribution of about 10% high-momentum nucleons, as experimentally determined by data from Jefferson Lab. These high-momentum nucleons provide a substantial contribution to the energy of the ground state, indicating a residual attractive contribution from higher-body interactions for 40 Ca of about 0.64 MeV/A.PACS numbers: 21.10. Pc,24.10.Ht,11.55.Fv The properties of a nucleon that is strongly influenced by the presence of other nucleons have traditionally been studied in separate energy domains. Positive energy nucleons are described by fitted optical potentials mostly in local form [1,2]. Bound nucleons have been analyzed in static potentials that lead to an independent-particle model modified by the interaction between valence nucleons as in traditional shell-model calculations [3,4]. The link between nuclear reactions and nuclear structure is provided by considering these potentials as representing different energy domains of one underlying nucleon self-energy. This idea was implemented in the dispersive optical model (DOM) by Mahaux and Sartor [5]. By employing dispersion relations, the method provides a critical link between the physics above and below the Fermi energy with both sides being influenced by the absorptive potentials on the other side.The DOM provides an ideal strategy to predict properties for exotic nuclei by utilizing extrapolations of these potentials towards the respective drip lines [6,7]. The main stumbling block so far has been the need to utilize the approximate expressions for the properties of nucleons below the Fermi energy that were developed by Mahaux and Sartor [5] to correct for the normalizationdistorting energy dependence of the Hartree-Fock (HF) potential. By restoring the proper treatment of nonlocality in the HF contribution, it was possible to overcome this problem [8] although the local treatment of the absorptive potentials yielded a poor description of the nuclear charge density and particle number.In the present work we have for the first time treated the nonlocality of these potentials for the nucleus 40 Ca with the aim to include all available data below the Fermi energy that can be linked to the nucleon single-particle propagator [9] while maintaining a correct description of the el...

The short-range and tensor components of the bare nucleon-nucleon interaction induce a sizeable depletion of low momenta in the ground state of a nuclear many-body system. The self-consistent Green's function method within the ladder approximation provides an \textit{ab-initio} description of correlated nuclear systems that accounts properly for these effects. The momentum distribution predicted by this approach is analyzed in detail, with emphasis on the depletion of the lowest momentum state. The temperature, density, and nucleon asymmetry (isospin) dependence of the depletion of the Fermi sea is clarified. A connection is established between the momentum distribution and the time-ordered components of the self-energy, which allows for an improved interpretation of the results. The dependence on the underlying nucleon-nucleon interaction provides quantitative estimates of the importance of short-range and tensor correlations in nuclear systems

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...