S. Marcos

On the sufficient conditions for the pseudospin symmetry in relativistic models

Abstract The reliability of the sufficient conditions for the pseudospin symmetry proposed for atomic nuclei has been analyzed, at a quantitative level, in the framework of the relativistic Hartree approximation (some effects of the exchange terms are also investigated). The contribution to the single-particle energy of the different terms appearing in the equation for the small component F of the Dirac spinor is calculated for the neutron pseudospin doublet states in the 40Ca and 208Pb nuclei. The F wave function is numerically calculated for the hypothetical case in which the symmetry is supposed to be exact.

Asymmetric nuclear matter in the relativistic approach

Abstract Bulk properties of asymmetric nuclear matter are studied in the Dirac-Hartree-Fock approximation. The model includes isoscalar (σ, ω) and isovector (π, ρ) mesons. The variations of binding energy, equilibrium density and compression modulus with increasing neutron excess are discussed and compared with predictions of non-relativistic Hartree-Fock calculations. The dependence of nucleon self-energies, effective masses and single-particle spectra on the neutron excess is also examined.

The excited dipole resonance: A finite-temperature sum rule approach

We present a systematic study of the evolution with excitation energy of the peak energy and width of the giant dipole resonance (GDR). The RPA moments m−1, m1 and m3 have been evaluated by means of a Thomas-Fermi method at finite temperatures (T < 3 MeV). We find that the peak energy decreases monotonically with temperature, although only by a small amount: ∼6% at T = 3 MeV. The width is found to increase by ∼20% in the same range of temperatures.

Magnetic susceptibility of neutron matter in a relativistic σ+ω+π+ϱ Hartree-Fock approach

Abstract A relativistic Hartree-Fock approach is used to study the magnetic susceptibility of a pure neutron system at relevant densities in neutron stars. Several combinations of mesons and couplings are used. The inclusion of isovector mesons crucially determines the possibility of a ferromagnetic transition. A π-meson pseudoscalar coupling favours the ferromagnetic phase whilst the pseudovector one inhibits it.

Magnetic properties of strongly asymmetric nuclear matter in a Dirac-Hartree-Fock approach

Abstract The magnetic susceptibility of strongly asymmetric nuclear matter, at relevant densities in neutron stars, is studied in the framework of a relativistic σ + ω + π + ϱ Hartree-Fock approach. The presence of protons, through their interaction with neutrons, means that formation of spontaneous magnetized matter occurs at lower densities than in pure neutron matter. A possible ferromagnetic transition is predicted at about four times the nuclear matter saturation density.

Semiclassical approximations in non-linear αω models

Abstract Extended Thomas-Fermi calculations up to second order in ħ have been performed for relativistic non-linear σω models and compared with the corresponding Hartree calculations. In several respects, the relativistic phenomenology quite resembles the one previously found in the non-relativistic context using Skyrme forces.

Description of nuclear systems within the relativistic Hartree–Fock method with zero-range self-interactions of the scalar field

An exact method is suggested to treat the nonlinear self-interactions (NLSI) in the relativistic Hartree–Fock (RHF) approach for nuclear systems. We consider here the NLSI constructed from the relativistic scalar nucleon densities including products of six and eight fermion fields. This type of NLSI corresponds to the zero-range limit of the standard cubic and quartic self-interactions of the scalar field. The method to treat the NLSI uses the Fierz transformation, which enables one to express the exchange (Fock) components in terms of the direct (Hartree) ones. The method is applied to nuclear matter and finite nuclei. It is shown that, in the RHF formalism, the NLSI, which are explicitly isovector-independent, generate scalar, vector and tensor nucleon self-energies with a strong isovector dependence. This strong isovector structure of the self-energies is due to the exchange terms of the RHF method. Calculations are carried out with a parametrization containing five free parameters. The model allows a description of both types of systems compatible with experimental data.

Magnetic susceptibility of neutron matter in a relativistic approach

Abstract A relativistic Hartree-Fock approach ( σ + ω ) is used to study the magnetic susceptibility of a pure neutron system at densities in the range of gravitationally stable neutron stars. A significant correlation is found between the expectation value of the relativistic spin operator and the magnetic susceptibility throughout this density range. The ferromagnetic transition is crucially determined by the Fock terms.

Investigation of a chiral model in the framework of a relativistic self-consistent calculation for atomic nuclei

The properties of finite nuclei are investigated in the framework of a chiral field theory using relativistic mean-field approximation. It is shown that, in contrast with the conventional point of view, the normal-type solutions for finite nuclei do exist. The authors have obtained these solutions and used them to calculate the nuclear bulk properties with two adjustable parameters. The mean-field normal solutions are not so far from the observed nuclei. The theory simultaneously contains also configurations of abnormal type which in some cases may appear to be much more strongly bound than those of the normal type. However, for conventional values of the scalar meson mass m sigma ( approximately 500 MeV) only one possibility remains-that of a normal configuration.

Pion tensor force and nuclear binding energy in the relativistic Hartree-Fock formalism

The binding energies of several isotopic families are studied within the relativistic Hartree-Fock approximation with the pseudovector coupling for the πN vertex, to find out a suitable strength for the effective pion tensor force (EPTF). An approximation for determining separately the contributions of the central and tensor forces generated by pion is considered. The results for heavy nuclei indicate that a realistic strength for the EPTF is smaller than a half of that appearing in the OPEP. This conclusion also applies to the results for the single-particle energies. Besides, it has been found that there is a genuine relativistic contribution of the EPTF in nuclear matter which is small but significant.