Using the relativistic mean-field model with nonlinear couplings between the isoscalar and isovector mesons, we study the properties of isospin-asymmetric nuclear matter. Not only the vector mixing, $\omega_{ \mu}\omega^{ \mu}\mathbf{ \rho}_{ \nu}\mathbf{ \rho}^{ \nu}$, but also the quartic interaction due to the scalar mesons, $\sigma^{ 2}\mathbf{ \delta}^{ 2}$, is taken into account to investigate the density dependence of nuclear symmetry energy, $E_{ \rm sym}$, and the neutron-star properties. It is found that the $\delta$ meson increases $E_{ \rm sym}$ at high densities, whereas the $\sigma$-$\delta$ mixing makes $E_{ \rm sym}$ soft above the saturation density. Furthermore, the $\delta$ meson and its mixing have a large influence on the radius and tidal deformability of a neutron star. In particular, the $\sigma$-$\delta$ mixing reduces the neutron-star radius, and, thus, the present calculation can simultaneously reproduce the dimensionless tidal deformabilities of a canonical $1.4M_{ \odot}$ neutron star observed from the binary neutron star merger, GW170817, and from the compact binary coalescence, GW190814.
Categories: nucl-th astro-ph.HE nucl-ex