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, omega ( mu ) omega ( mu ) rho ( nu ) rho ( nu ), but also the quartic interaction due to the scalar mesons, sigma (2) delta (2), is taken into account to investigate the density dependence of nuclear symmetry energy, E (sym), and the neutron star properties. It is found that the delta meson increases E (sym) at high densities, whereas the sigma-delta mixing makes E (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; thus, the present calculation can simultaneously reproduce the dimensionless tidal deformabilities of a canonical 1.4 M (circle dot) neutron star observed from the binary neutron star merger GW170817 and the compact binary coalescence GW190814.

Automated summary

Using the relativistic mean-field model, this study investigates the properties of isospin-asymmetric nuclear matter, considering the couplings between isoscalar and isovector mesons. The effects of vector mixing and quartic interactions on nuclear symmetry energy and neutron star properties are examined. The findings reveal that the delta meson increases nuclear symmetry energy at high densities, while the mixing of sigma and delta mesons softens the symmetry energy above the saturation density. The delta meson and its mixing also have a significant influence on the radius and tidal deformability of a neutron star. In particular, the mixing reduces the neutron star radius, allowing for a simultaneous reproduction of the observed tidal deformabilities of neutron stars.