Nuclear equation of state in relativistic mean-field models with isoscalar- and isovector-meson mixing

We construct nuclear equation of state (EoS) of dense matter using the relativistic mean-field (RMF) model with nonlinear couplings. Taking into account the results of neutron skin thickness of ²⁰⁸Pb and ⁴⁸Ca by the PREX-2 and CREX experiments as well as the particle flow data in heavy-ion collisions, the observed mass of PSR J0740+6620, and the tidal deformability of a neutron star from GW170817, we build new effective interactions in the RMF model with the isovector, Lorentz-scalar (δ) meson. In addition, we study the effect of isoscalar- and isovector-meson mixing, σ²δ² and ω_μω^μρ_ν·ρ^ν, on the properties of finite nuclei, nuclear matter, and neutron stars. It is found that the σ-δ mixing is very useful to understand the recent nuclear experiments and astrophysical observations of neutron stars simultaneously. Especially, the EoS of neutron stars exhibits the rapid stiffening around twice the nuclear saturation density, which is caused by the unique behavior of nuclear symmetry energy due to the σ-δ mixing. It is also interesting that the small dimensionless tidal deformability of a canonical neutron star observed from GW170817 can be satisfied within the RMF models with isoscalar- and isovector-meson mixing.