Impact of isoscalar- and isovector-meson mixing on properties of asymmetric nuclear matter in relativistic mean-field models

Using the relativistic mean-field model with the isoscalar- and isovector-meson mixing, ${\sigma }^2{\delta }^2$ and ${\omega }_{\mu }{\omega }^{\mu }{\rho }_{\nu }{\rho }^{\nu }$, we construct a new nuclear equation of state, which satisfies the large neutron skin thickness of ²⁰⁸Pb and the small radius of a neutron star, respectively reported by the PREX-2 experiment and the NICER observation. We study the effects of δ meson and σ-δ mixing on the properties of nuclear and neutron-star matter through the density dependence of nuclear symmetry energy, $E_{\mathrm{sym}}$. It is found that the δ meson increases $E_{\mathrm{sym}}$ at high densities, while the σ-δ mixing softens $E_{\mathrm{sym}}$ above the saturation density to explain the tidal deformability of a neutron star observed from GW170817.