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Asymmetric nuclear matter in relativistic mean-field models with isoscalar- and isovector-meson mixing

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, $ω_μω^μ\mathbfρ_ν\mathbfρ^ν$, but also the quartic interaction due to the scalar mesons, $σ^{2}\mathbfδ^{2}$, 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 $δ$ meson increases $E_{\rm sym}$ at high densities, whereas the $σ$-$δ$ mixing makes $E_{\rm sym}$ soft above the saturation density. Furthermore, the $δ$ meson and its mixing have a large influence on the radius and tidal deformability of a neutron star. In particular, the $σ$-$δ$ 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.