Proton Fraction in Neutron Star Matter and Three-Body Force Effects

The three-body force effects on the equation of state and its iso-spin dependence of asymmetric nuclear matter and on the proton fraction in neutron star matter have been investigated[1] within Brueckner Hartree-Fock (BHF) approach by using a microscopic three-body force. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry β=(N-Z)/A is fulfilled in the whole asymmetry range 0 ≤β ≤1 and also up to high density. The three-body force provides a strong enhancement of symmetry energy at high density in agreement with relativistic approaches. Thecalculated proton fraction in β stable neutron star matter is given in Fig.l, where the thick solid line is the BHF prediction using AV18+TBF, while the dotted one is the BHF result using AVis. The thin solid line is the prediction of the Dirac-Brueckner approach taken from Ref.[2]. The results extracted according to the phenomenological paramete rizations of the symmetry energy suggested in Ref.[3] are also plotted. It is seen

Effective Mass of Kaon in Asymmetric^1 Nuclear Matter

The properties of kaon at very high baryon density has been a fascinating subject since 1986. Of particular importance is the modification of effective mass of antikaon in-medium. This is expected to not only help us to understander the chiral symmetry restoration but also effect the composition and structure of neutron star.. The modification of kaon and antikaon mass in medium might be a new mechanism of production at energies below the threshold. Based on the mean-field approximation to the effective SU(3)L×SU(3)n chiral Lagrangian, the kaon and anti kaon mass in medium, defined as the energy of a kaon (or antikaon) with zero three momentum,are then given by[1]

Equation of State of Asymmetric Nuclear Matter at Finite Temperature with a Three-body Force

In the present work, the equation of state of hot asymmetric nuclear matter nas Been investigated in the framework of the finite temperature Brueckner-Hartree-Fock (FTBHF) approach with a microscopic three-body force (TBF). The temperature dependence and the isospin dependence of the single particle properties, such as the proton and neutron single-particle potentials and effective masses have been studied. It is shown that the TBF gives a repulsive contribution to the proton or neutron single particle potential. The energy per nucleon versus asymmetry parameter is found to fulfill a parabolic relation as in the zero temperature case[I]. This means that the symmetry energy at finite temperature Esym can be extracted from' the energy difference between pure neutron matter and symmetric matter. The calculated symmetry energy is plotted in Fig.1.

Three—Body Force Effects on EOS of Asymmetric Nuclear Matter and Proton Fraction in Neutron Star Matter

The three-body force effects on the equation of state and its iso-spin dependence of asymmetric nuclear matter and on the proton fraction in neutron star matter have been investigated within Brueckner-Hartree-Fock approach by using a microscopic three-body force. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry is fulfilled in the whole asymmetry range and also up to high density. The three-body force provides a strong enhancement of symmetry energy at high density in agreement with relativistic approaches. It also shows that the three-body force leads to a much more rapid increasing of symmetry energy with density in relatively high density region and to a much lower threshold density for the direct URCA process to occur in a neutron star as compared to the predictions adopting only pure two-body force.

Nucleon ~3pF_2 Superfluid Pairing Gap in Asymmetry Nuclear Matter

The 3 P F2 superfluidity of neutron and proton is investigated in isospin-asymmetric nuclear matter within the Brueckner-Hartree-Fock approach and the BCS theory by adopting the Argonne V14 and the Argonne V18 nucleonnucleon interactions. We find that pairing gaps in the 3PF2 channel predicted by adopting the AV14 interaction are much larger than those by the AV18 interaction. As the isospin-asymmetry increases, the neutron 3 pF2 superfluidity is found to increase rapidly, whereas the proton one turns out to decrease and may even vanish at high enough asymmetries. As a consequence, the neutron 3pF2 superfluidity is much stronger than the proton one at high asymmetries and it predominates over the proton one in dense neutron-rich matter.

R-mode Instability of Neutron Star with Non-Newtonian Gravity

The Chandrasekhar-Friedmann-Schutz （CFS） instabilities of r-modes for canonical neutron stars （1.4 Me） with rigid crusts are investigated by using an equation of state of asymmetric nuclear matter with super-soft symmetry energy, where the non-Newtonian gravity proposed in the grand unification theories is also considered. Constrained by the observations of the masses and the spin frequencies for neutron stars, the boundary of the r-mode instability window for a canonical neutron star is obtained, and the results show that the observed neutron stars are all outside the instability window, which is consistent with the theoretical expectation. In addition, an upper limit of the non-Newtonian gravity parameters is also given.