Influence Of Nuclear Symmetry Energy On Properties Of Neutron Star Outer Core Matter

The evolution,structure of neutron stars and the properties of its matter are summarized,and the influence of nuclear symmetry energy on nuclear matter and neutron star matter are described in this article.Based on the mean-field approximation of relativistic ?-?-? model,the expressions of energy density,pressure and nuclear symmetry energy of nuclear matter were derived,and the influence of nuclear symmetry energy on neutron star outer core matter is studied.The studies in this paper are divided into two parts.The first part,based on the relativistic ?-?-? model with the nonlinear self-interaction of ? meson and density-dependent nucleon-meson coupling constants,respectively,the influences of the parameters of nucleon-nucleon interaction on the properties of nuclear matter are studied.The results showed that the parameters of nucleon-nucleon interaction can effectively modify the equation of state of nuclear matter and incompressibility coefficient predicted by models,the density-dependent of nuclear symmetry energy was mainly impacted by the parameter a_?,which indicated that the properties of nuclear symmetry energy were mainly reflected by the isospin vector-vector ? meson.The second part,on the base of previous works,combined the constraint of the neutron star,we selected some appropriate model to study the influence of nuclear symmetry energy on properties of neutron star outer core matter,and compared with the results of the skyrme models.It is found that greater nuclear symmetry energy in high density region and slope at saturation density produce greater proton fraction and pressure of neutron star outer core matter.And the density threshold of proton superfluidity and the direct URCA process,which are model dependent,decrease as the nuclear symmetry energy increases.The density threshold of direct URCA process is greater than 4?₀ except the model NL1and DDC1,but the incompressibility coefficient of NL1 and DDC1 has exceeded the reasonable value,so the direct URCA process will appear in the greater density region.