Effective Nuclear Model Research Articles

Compact stars in the pseudo-complex general relativity

The field equations of the pseudo-complex General Relativity (pc-GR) have an extra term, of repulsive character, which may halt the gravitational attractive collapse of matter distributions in the evolution process of compact stars. This additional extra term simulates the presence of dark energy in the Universe. On the first part of this contribution we consider the effect of this additional term of pc-GR on the structure of a white dwarf. Observations of type Ia supernova (SNe Ia) admit white dwarfs with masses as high as 2.3M⊙ − 2.6M⊙, surpassing this way the mass limit established by Chandrasekhar (1.44M⊙). In a more conventional theoretical description of a white dwarf, the electron degeneracy pressure ultimately stabilizes the star against gravitational collapse and establishes this way the Chandrasekhar maximum limit of the stelar mass; this mechanism can not explain however values of masses more expressive like those mentioned above. We investigate here a possible mechanism for carrying out such a hypothesis: the combination of the electron degeneracy and dark energy internal pressures. In this study we use a very simple model for the white dwarf mater which consists of nucleons and degenerate electrons, held together by the presence of the gravitational interaction and superimposed to a repulsive background of dark energy. In the pc-GR formalism, the corresponding modified Tolman-Oppenheimer-Volkoff (TOV) equations are solved and the mass-radius relations as well as the maximum mass of the white dwarf star are determined for different parameter configurations. In the second part of this contribution we explore the presence of this additional term and study the role of dark energy in the structure of neutron stars composed by nucleons, hyperons, mesons, and weakly interacting massive fermion dark matter particles (WIMPs) held together by the presence of the nuclear force and the gravitational interaction, superimposed to the repulsive background of dark energy. To describe the hadron-lepton sector we consider three different effective nuclear models, Zimanyi-Moszkowski, Boguta-Bodmer, and the analytic parametrized coupling model, which we extend to consider, in the baryonic sector, the presence of the whole fundamental baryon octet. By solving the corresponding pc-GR Tolman-Oppenheimer-Volkoff (TOV) equations we estimate the maximum gravitational mass of neutron stars.

An effective Nuclear Model: from Nuclear Matter to Finite Nuclei

The momentum and density dependence of mean fields in symmetric and asymmetric nuclear matter are analysed using the simple density dependent finite range effective interaction containing a single Gaussian term alongwith the zero-range terms. Within the formalism developed, it is possible to reproduce the various diverging predictions on the momentum and density dependence of isovector part of the mean field in asymmetric matter. The finite nucleus calculation is formulated for the simple Gaussian interaction in the framework of quasilocal density functional theory. The prediction of energies and charge radii of the interaction for the spherical nuclei compares well with the results of other effective theories.

Properties of Strange Matter in a Model with Effective Lagrangian**The project supported in part by National Natural Science Foundation of China under Grant Nos 19975060 and 19975010 and the Foundation from the Chinese Academy of Sciences under Grant No. KJ 951-A1-410

The strange hadronic matter with nucleons, -hyperons and -hyperons is studied by using an effective nuclear model in a mean-field approximation. The density and strangeness fraction dependence of the effective baryon masses as well as the saturation properties and stabilities of the strange hadronic matter are discussed.

Application of an effective gauge-invariant model to nuclear matter inthe relativistic Hartree-Fock approximation

An effective nuclear model describing ω-, ρ- and axial-mesonsas gauge fields is applied to nuclear matter in the relativisticHartree-Fock approximation. The isoscalar two-pion exchange issimulated by a scalar field s similar to that used in the conventionalrelativistic mean-field approach. Two more scalar fields are essentialingredients of the present treatment:the σ-field, the chiral partner of the pion, and the Σ-field,the Higgs field for the ω-meson. Two versions of the model areused depending on whether the σ-field is considered as adynamical variable or `frozen', by taking its mass as infinite. The modelcontains four free parameters in the first case and three in the second onewhich are fitted to the nuclear matter saturation conditions.The nucleon and meson effective masses, compressibility modulus andsymmetry energy are calculated. The results prove the reliability of theDirac-Hartree-Fock approach within the linear realization of the chiralsymmetry.

Asymmetric nuclear matter at finite temperature and density

Asymmetric nuclear matter is studied by using an effective nuclear model in a mean-field approximation. The density, temperature, and asymmetric parameter dependence of the effective baryon mass is discussed. The liquid-gas phase transition of a system with two independent conserved charges (baryon number and isospin) is studied using the stability conditions on the free energy and Gibbs conditions for phase equilibrium. The critical temperature is calculated with and without $\ensuremath{\rho}$ meson contribution, respectively.