Studies On Baryon Direct URCA Processes In Neutron Star

The study on the properties of the thermal evolution of neutron star is one of the hot issues in the field of nuclear astrophysics. This paper is mainly in the framework of the relativistic mean field(RMF) and relativistic Hartree-Fork theories. With the consideration of the SU(3) flavor symmetry hyperon-meson coupling, the δ meson and the interaction of tensor and mesons, this paper obtains the following three results in the direct URCA processes in neutron stars.Firstly, we study the properties of the baryon direct URCA process in neutron stars by using GM1 and TM1 parameters based on the framework of RMF theory. On the one hand, we adopt two methods of hyperon-meson coupling parameters, the SU(6) spin-flavor and SU(3) flavor symmetry, to study the properties of the nucleon and hyperon direct URCA processes in neutron star matter. The calculated results show that the existence of hyperons reduces the abundance of protons and leptons and results in less the neutrino emissivity of the nucleon direct Urca processes. On the other hand, we investigate the influence of degree of fredom of hyperons on the total neutrino emissivity and neutrino luminosity for the baryon direct URCA processes. The results show that the neutrino emissivity of the nucleon direct URCA processes for SU(3) flavor symmetry is higher than that in SU(6) symmetry in the most area of the baryon number density. The IV hyperon direct URCA processes have the similar trend. In addition, Whether or not hyperons appear in neutron star, the total neutrino luminosity for the baryon direct URCA processes increases firstly and then decreases. This means that the same neutrino luminosity corresponds to two different mass neutron stars.Secondly, we study the influence of the isovector scalar ? meson on the nucleon and hyperon direct URCA processes in hyperonic neutron star. The calculation results show that with the inclusion of ? meson, the effective masses of nucleons and hyperons split. And the fractions of p, Λ、Σ0、Σ- significantly increase. The presence of the ? meson also makes that the neutrino emissivity of the nucleon and hyperon direct Urca processes increases, and thus accelerates the cooling of neutron star matter.Finally, We stud the influences of the tensor couplings of vector mesons ω and ρ on the nucleon direct URCA processes and the 01 nucleon superuidity within the relativistic Hartree-Fock approximation in npe? matter.The results show that the inclusion of the tensor couplings of vector mesons ω and ρ leads to obvious enhancement of the neutrino emissivity for the nucleon direct URCA processes when the nucleon density ρ?0.42fm-3. Besides that, It is found that the tensor couplings of vector mesons ω and ρ lead to a clear growth of the 01 neutron pairing gap in the density range of existing 01 neutron superuidity. Specifically, the peak value of the 01 neutron pairing gap increases by 44% over the cprresponding value without the tensor couplings of vector mesons ω and ρ. In addition, in the density ranges of ρ = 0.0~0.079fm-3 and ρ =0.079~0.383fm-3, the 01 pairing gap of proton with the tensor couplings of vector mesons ω and ρ is first lower and then higher the corresponding values without the tensor couplings of vector mesons ω and ρ, respectively. These changes must change the properties of neutron star cooling. Our results provide a basic to understand the influence of the tensor couplings of vector mesons ω and ρ on the cooling properties of neutron star.