Neutron star properties in density-dependent relativistic mean field theory with consideration of an isovector scalar meson

Abstract

Based on the density-dependent relativistic mean field theory, the properties for nuclear matter and neutron stars with the effective interaction $\mathrm{DD}\text{\ensuremath{-}}\mathrm{ME}\ensuremath{\delta}$ including the isovector scalar channel which disentangle the effects of isovector scalar and isovector vector channels by fitting microscopic calculations. The influences of the isovector scalar $\ensuremath{\delta}$ meson on properties of asymmetric nuclear matter at high densities are discussed in detail. The results support that the isovector scalar channel can soften the equation of state through the effects on the nucleon effective mass and the scalar $\ensuremath{\sigma}$ field and impact the behavior of the nuclear matter symmetry energy. Because of the influence on the symmetry energy by the $\ensuremath{\delta}$ meson, a larger proton fraction in neutron stars is predicted by the $\mathrm{DD}\text{\ensuremath{-}}\mathrm{ME}\ensuremath{\delta}$ calculation, which strongly affects the cooling process of the star. The maximum masses of neutron stars given by the $\mathrm{DD}\text{\ensuremath{-}}\mathrm{ME}\ensuremath{\delta}$ calculation is $1.97{M}_{⨀}$ which is in reasonable agreement with PSR J1614 \ensuremath{-} 2230 ($1.97 \ifmmode\pm\else\textpm\fi{} 0.04 {M}_{⨀}$) and PSR J0348 + 0432 $(2.01 \ifmmode\pm\else\textpm\fi{} 0.04 {M}_{⨀})$. Among all the selected interactions, $\mathrm{DD}\text{\ensuremath{-}}\mathrm{ME}\ensuremath{\delta}$ gives the smallest radius range. The radius for the 1.4 solar mass neutron star calculated by $\mathrm{DD}\text{\ensuremath{-}}\mathrm{ME}\ensuremath{\delta}$ is in good agreement with the prediction [Astrophys. J. Lett. 765, L5 (2013)] according to the resent observations.