Nature Of Neutron Star Matter In Extreme Environments

The effects of strong magnetic fields on neutron star matter are investigated in the quark-meson coupling(QMC) model.The QMC model describes a nuclear many-body system as nonoverlapping MIT bags in which quarks interact through self-consistent exchange of scalar and vector mesons in the mean-field approximation.The results of the QMC model are compared with those obtained in a relativistic mean-field(RMF) model.It is found that quantitative differences exist between the QMC and RMF models, while qualitative trends of the magnetic field effects on the equation of state and composition of neutron star matter are very similar.We study the effects of strong magnetic fields on antikaon condensation in neutron star matter using the quark-meson coupling(QMC) model.It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly. The onset of K^- condensation stronger depends on the magnetic field strength, and it even shifts beyond the threshold of(?)⁰ condensation for sufficiently strong magnetic fields.In the presence of strong magnetic fields,the equation of state(EOS) becomes stiffer in comparison with the field-free case.The softening of the EOS by antikaon condensation also depends on the magnetic field strength,and it becomes less pronounced with increasing magnetic field strength.The results of the QMC model are compared with those obtained in a relativistic mean-field(RMF) model,and we find there are quantitative differences between the results of the QMC and RMF models.We study the effects of strong magnetic fields on the properties of hyperonic matter. We employ the relativistic mean field theory which is known to provide excellent descriptions of nuclear matter and finite nuclei.The two additional hidden-strangeness mesons,ρ^* andφ,are taken into account,and some reasonable hyperon potentials are used to constrain the meson-hyperon couplings,which reflect the recent developments in hypernuclear physics.It is found that the effects of strong magnetic fields become significant only for magnetic field strength B＞5×10¹⁸ G.The threshold densities of hyperons can be significantly altered by strong magnetic fields.The presence of hyperons makes the equation of state(EOS) softer compared to the case without hyperons, and the softening of the EOS becomes less pronounced with increasing magnetic field strength.We study the properties of antikaon condensation in neutron star matter including the effects of temperature using the relativistic mean field theory.It is found that the effects of temperature below 10 MeV is not significant on altering the threshold density of antikaon condensation.In the presence of temperature,the equation of state(EOS) becomes stiffer in comparison with the zero-temperature case.