Superfluid nuclear matter in BCS theory and beyond

Medium polarization effects are studied for ¹S₀ pairing in nuclear matter within BHF approach. The screening potential is calculated in the RPA limit, suitably renormalized to cure the low density mechanical instability of nuclear matter. The self-energy corrections are consistently included resulting in a strong     

Isospin-dependent relativistic microscopic optical potential in the Dirac Brueckner-Hartree-Fock method

There is growing evidence to suggest that the binding energy of nucleon in nuclear matter comes from a cancellation between large Lorentz scalar and vector potentials[1,2]. The relativistic approach has been of a great success in describing not only the ground state properties of stable nuclei, but also those of exotic nuclei. In the relativistic frame, the spin-orbit coupling can be deduced automatically, which is usually given by hand in the non-relativistic approach. The relativistic method…     

Saturation of nuclear matter and realistic interactions

In this communication we study symmetric nuclear matter for the Brueckner-Hartree-Fock approach, using two realistic nucleon-nucleon interactions (CD-Bonn and Bonn C). The single-particle energy is calculated self-consistently from the real on-shell self-energy. The relation between different expressions for the pressure is studied in cold nuclear matter. For best calculations the self-energy is calculated with the inclusion of hole-hole (hh) propagation. The effects of hh contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Using two different methods, namely, G-matrix and bare potential, the hh term is calculated. We found that using G-matrix brought about non-negligible contribution to the self-energy, but this difference is very small and can be ignored if compared with the large contribution coming from particle-particle term. The contribution of the hh term leads to a repulsive contribution to the Fermi energy which increases with density. For extended Brueckner-Hartree-Fock approach the Fermi energy at the saturation point fulfills the Hugenholtz-Van Hove relation.     

核势和核子有效质量的同位旋相关性

在Dirac Brueckner Hartree-Fock (DBHF)理论框架下研究了核子光学势和核子有效质量的同位旋相关性. 非对称核物质的计算采用了DBHF的核子自能的Dirac结构的新的分解方法, 核子自能的实部是用G矩阵在Hartree-Fock近似下计算得到, 而虚部从极化图得到. 用核子的薛定谔等价势可以得到核子矢量有效质量. 研究表明考虑了核势的能量相关性在丰中子核物质情况下核子矢量有效质量比质子的大.     

Correlations and the Dirac structure of the nucleon self-energy

The Dirac structure of the nucleon self-energy in symmetric nuclear matter as well as neutron matter is derived from a realistic meson exchange model for the nucleon-nucleon (NN) interaction. It is demonstrated that the effects of correlations on the effective NN interaction in the nuclear medium can be parameterized by means of an effective meson exchange. This analysis leads to a very intuitive interpretation of correlation effects and also provides an efficient parametrization of an effective interaction to be used in relativistic structure calculations for finite nuclei. Received: 29 January 2001 / Accepted: 5 May 2001     

Temperature-Dependent Imaginary Part of the Off-Shell Nucleon Self-Energy and the Second Order Correction of Real Part of the Nucleon Self-Energy

The imaginary part of the off-shell nucleon self-energy at finite temperature in nuclear matter, where the polarization and correlation contributions of exchanges of the meson are taken into account, is investigated based on Walecka's meson-nucleon model and thermofield dynamics. The second order correction of temperature-dependent real part of the nucleon self-energy is calculated in terms of the dispersion relation. The Schrodinger equivalent potential of relativistic microscopic optical potential of a nucleon at finite temperature in nuclear medium is also studied.     

On the Dirac structure of the nucleon self-energy in nuclear matter

The relativistic structure of the self-energy of a nucleon in nuclear matter is investigated including the imaginary and real components which arise from the terms of first and second order in the NN interaction. A parameterized form of the Brueckner G-matrix is used for the NN interaction. The effects of the terms beyond the DBHF approximation on quasiparticle energies and the optical potential for nucleon-nucleus scattering are discussed.     

Modifications of single-particle properties in nuclear matter induced by three-body forces

Within the self-consistent Green’s function formalism, we study the effects of three-body forces on the in-medium spectral function, self-energy and effective mass of the nuclear matter constituents, analyzing the density and momentum dependence.     

The mass of a bound Δ-isobar

The properties of the Δ -isobar when bound in the nuclear medium are studied. The pionnucleon resonance nature of the Δ -isobar yields self-energy corrections, i.e., an energy- and medium-dependent mass and, above pion-production threshold, an energy- and medium-dependent width. Their importance on nucleon-nucleon scattering, the three-nucleon bound state and nuclear matter are discussed. Other effects arising from the resonance nature of the Δ -isobar are the retardation of the two-body interaction, three-nucleon forces and e.m. exchange currents.     

In-medium two-nucleon properties in high electric fields

The quantum mechanical two — particle problem is considered in hot dense nuclear matter under the influence of a strong electric field such as the field of the residual nucleus in heavy — ion reactions. A generalized Galitskii-Bethe-Salpeter equation is derived and solved which includes retardation and field effects. Compared with the in-medium properties in the zero-field case, bound states are turned into resonances and the scattering phase shifts are modified. Four effects are observed due to the applied field: (i) A suppression of the Pauli-blocking below nuclear matter densities, (ii) the onset of pairing occurs already at higher temperatures due to the field, (iii) a field dependent finite lifetime of deuterons and (iv) the imaginary part of the quasiparticle self-energy changes its sign for special values of density and temperatures indicating a phase instability. The latter effect may influence the fragmentation processes. The lifetime of deuterons in a strong Coulomb field is given explicitly.     

In-medium two-nucleon properties in high electric fields

The quantum mechanical two — particle problem is considered in hot dense nuclear matter under the influence of a strong electric field such as the field of the residual nucleus in heavy — ion reactions. A generalized Galitskii-Bethe-Salpeter equation is derived and solved which includes retardation and field effects. Compared with the in-medium properties in the zero-field case, bound states are turned into resonances and the scattering phase shifts are modified. Four effects are observed due to the applied field: (i) A suppression of the Pauli-blocking below nuclear matter densities, (ii) the onset of pairing occurs already at higher temperatures due to the field, (iii) a field dependent finite lifetime of deuterons and (iv) the imaginary part of the quasiparticle self-energy changes its sign for special values of density and temperatures indicating a phase instability. The latter effect may influence the fragmentation processes. The lifetime of deuterons in a strong Coulomb field is given explicitly.     

Optical potentials in relativistic meson-nucleon model

The relativistic microscopic optical potentials (RMOP) at E < 300 MeV have been derived and investigated based on Walecka's meson-nucleon model. An effective lagrangian including nucleon, σ- and ω-mesons, which is required to reproduce the nuclear matter saturation properties, has been introduced and used to calculate the self-energy of a nucleon in the nuclear medium. Systematical analyses of the scattering data are performed with the RMOP. Finally, several effects, such as the meson-nucleon vertex form factor, isovector meson exchanges, non-linear σ-model are studied.     

Study of the Binding Energy of Relativistic Nuclear Matter in the Relativistic σ-ω-π Model

A relativistic σ-ω-π model is proposed to calculate the binding energy of relativistic nuclear matter. We put emphasis on the relativistic particle-hole, delta-hole excitation of pion propagator in nuclear matter. The renormalization of the nucleon self-energy in nuclear matter is made for the pseudo-vector πNN and πNΔ couplings by introducing corresponding form factor and by dispersion relation. We find that the density dependence correction to meson-NN coupling constants is very important to saturate the binding energy of nuclear matter. The density dependence correction to πNN and πNΔ coupling constants has the effect of softening the EOS of nuclear matter.     

Damping of Single-Particle in Slab Model at Finite Temperature

The temperature dependence of the self-energy of a particle is studied in semi-infinite nuclear matter by making use of interactions constrained by self-consistency. Using the finite temperature Green's function Matsubara formulism, and applying the theory of slab model to the single-particle states in ²⁰⁸Pb, the calculated results show that the imaginary parts of the self-energy of a particle at Fermi energy linearly increase with the increase of temperature.     

中子物质中超流性的自能色散效应

利用扩展的 Brueckner- Hartree- Fock理论与推广的 BCS方法研究了自能的色散效应和基态关联对中子物质中超流性和能隙的影响 .研究结果表明 ,自能的色散效应使中子物质中能隙减小;考虑基态关联后 ,超流性将进一步减弱. The effects of the dispersion and ground state correlation of the single particle self-energy on neutron matter superfluidity have been investigated in the framework of the Extended Brueckner-Hartree-Fock and the generalized BCS approaches. A sizable reduction of the energy gap is found due to the energy dependence of the self-energy. And the inclusion of the ground state correlations in the self-energy suppresses further the neutron matter superfluidity.     

Thermodynamical consistent CJT calculation in studying nuclear matter

We have attempted to apply the CJT formalism to study the nuclear matter. The thermodynamic potential is calculated in Hartree–Fock approximation in the CJT formalism. In the calculation, as the first step, we have neglected the medium effects to the mesons, the momentum dependence in the nucleon self-energy and the fluctuations of the vacuum. After these approximations, the numerical results are found very consistent with those obtained from the mean field calculation. In our calculation the thermodynamical consistency is also preserved.     

The nuclear symmetry energy from relativistic Brueckner-Hartree-Fock model

The microscopic mechanisms of the symmetry energy in nuclear matter are investigated in the framework of the relativistic Brueckner-Hartree-Fock (RBHF) model with a high-precision realistic nuclear potential, pvCDBonn A. The kinetic energy and potential contributions to symmetry energy are decomposed. They are explicitly expressed by the nucleon self-energies, which are obtained through projecting the G-matrices from the RBHF model into the terms of Lorentz covariants. The nuclear medium effects on the nucleon self-energy and nucleon-nucleon interaction in symmetry energy are discussed by comparing the results from the RBHF model and those from Hartree-Fock and relativistic Hartree-Fock models. It is found that the nucleon self-energy including the nuclear medium effect on the single-nucleon wave function provides a largely positive contribution to the symmetry energy, while the nuclear medium effect on the nucleon-nucleon interaction, i.e., the effective G-matrices provides a negative contribution. The tensor force plays an essential role in the symmetry energy around the density. The scalar and vector covariant amplitudes of nucleon-nucleon interaction dominate the potential component of the symmetry energy. Furthermore, the isoscalar and isovector terms in the optical potential are extracted from the RBHF model. The isoscalar part is consistent with the results from the analysis of global optical potential, while the isovector one has obvious differences at higher incident energy due to the relativistic effect.     

Dissociation of Hadrons in Quark Matter Within a Finite-Temperature Field-Theory Approach on the Light Front

We present a relativistic three-body equation to investigate the properties of nucleons in hot and dense nuclear/quark matter. Within the light-front approach we utilize a zero-range interaction to study the three-body dynamics. The relativistic in-medium equation is derived within a systematic Dyson equation approach that includes the dominant medium effects due to Pauli blocking and self-energy corrections. We present the in-medium nucleon mass and calculate the dissociation of the three-body system.     

Temperature Dependent Relativistic Microscopic Optical Potential and Mean Free Paths of Nucleons

The microscopic optical potential,mean free paths and Schrodinger equivalent potential of nucleons at finite temperature in nuclear matter are studied based on Walecka's model and thermo field dynamics.We let only the Hartree-Fock self-energy of nucleon represent to be the real part of the microscopic optical potential and the fourth order of meson exchange diagrams,i.e. the core polarization represent the imaginary part of microscopic optical potential in nuclear matter.The microscopic optical potential of finite nuclei is obtained with the local density approximation.