Narrow Results

In the mean field approximation of the relativistic σ-ω-ρ model, the magnetic fields are incorporated, and it's influence on the properties of n-p-e neutron star matter are studied. When the strength of the magnetic field is weaker than ~10¹⁸G, the particles' fractions and chemical potentials, matter's energy density and pressure hardly change with the magnetic field; when the strength of the magnetic field is stronger than ~10²⁰G, the above quantities change with the magnetic field evidently. Furthermore, the pressure is studied in both thermodynamics and hydrodynamics. The difference between these two ways exits in the high density region, that is, the thermal self-consistency may not be satisfied in this region if the magnetic field is considered.

High density behavior of nuclear symmetry energy is studied on the basis of the stiffest density dependence of asymmetric contribution to energy per nucleon in charge neutral n + p + e + $\mu$ matter under beta equilibrium. The density dependence of nuclear symmetry energy obtained in this way is neither very stiff nor soft at high densities and is found to be in conformity with recent observations of neutron stars.

Many calculations of the neutron star (NS) equation of state (EOS) have been performed over the years. Recent observations of NSs have begun to play an important role in finding the realistic EOS. In this paper, we compare mass–radius relations derived from various EOSs with observational data of NSs. In addition, we adjust EOSs to be consistent with observational data from NSs and employ Bayesian statistical analyses to obtain constraints on the EOS. Our results show that the EOS needs to be softened in the medium density region ($2{\rho }_0$–$4{\rho }_0$, where ${\rho }_0$ is the saturation density) and to have a rapid change of stiffness around an energy density of $\sim$ 650 MeV/fm³.

In the present paper, we study exotic phases in hot neutron–proton–electron (NPE) matter. It is shown that for densities lower than the normal nuclear matter inhomogeneous (exotic or pasta) phases may be present. This is believed to occur due to the so-called frustration mechanism, i.e., a close competition between the surface and Coulomb energy which, in certain cases, favors exotic phases instead of homogeneous matter. These structures may have important effects in the cooling of neutron stars, for example, affecting the neutrino opacity.

Relativistic mean-field theory with parameter sets FSUGold and IU-FSU is extended to study the properties of neutron star matter in β equilibrium by including Kaon condensation. The mixed phase of normal baryons and Kaon condensation cannot exist in neutron star matter for the FSUGold model and the IU-FSU model. In addition, it is found that when the optical potential of the K^- in normal nuclear matter U_K ≳ -100 MeV, the Kaon condensation phase is absent in the inner cores of the neutron stars.

In this paper, magnetic field and equation of state (EoS) of neutron star matter are studied under relativistic mean field theory. A nonzero mass term of magnetic field in the Lagrangian is introduced, which depends on baryon density of charged particles. The magnetic field has not been treated as external as usual and the calculations of magnetic field strength at finite temperature reveal the existence of inflection points in certain densities.

In this theoretical study, we report an investigation of the equations of state (EoSs) of hyper-nuclear matter and its composition as a function of density within the framework of effective field theory motivated relativistic mean field model. We have used G2 force parameter along with various hyperon–meson coupling ratios by allowing the mixing and the breaking of SU(6) symmetry to predict the EoSs, keeping the nucleonic coupling constant intact. We have estimated the properties of nonrotating and rapidly rotating configuration of compact stars by employing four different representative sets of equations of state. The obtained results of the mass and radius for the compact stars are compared with the recent mass observations. Further, we have studied the stability and sensitivity of rotational frequency (at sub-millisecond period) on the configuration of the compact stars because the angular frequency is significantly smaller than the mass-shedding (Keplerian) frequency in slow rotation regime. Moreover, the yield of hyperon as a function of density for various hyperon–meson couplings are also estimated.

The magnetic susceptibility of spin-polarized neutron matter is calculated at both zero and finite temperature within (i) the microscopic framework of the Brueckner-Hartree-Fock formalism, and (ii) using the Skyrme and Gogny phenomenological forces. The microscopic results show no indication of a ferromagnetic transition at any density and temperature. In the case of the Skyrme interaction, it is shown that the critical density at which ferromagnetism takes place decreases with temperature. This unexpected feature is associated to an anomalous behavior of the entropy that becomes larger for the polarized phase than for the unpolarized one above a certain critical density. For the Gogny force, the results show two different behaviors: whereas the D1P parametrization exhibits a ferromagnetic transition at a density of ρ ~ 1.31 fm^-3 whose onset increases with temperature, no sign of such a transition is found for D1 at any density and temperature, in agreement with the microscopic calculations.