Isospin-Asymmetric Cold Nuclear Matter in the Relativistic Mean-Field Theory with a Scalar-Isovector Interaction Channel

The properties of isospin-asymmetric cold nuclear matter are studied in terms of the relativistic mean-field theory in which, besides the fields of σ, ω, and ρ mesons, and the isovector, Lorentz-scalar field of the δ-meson is also taken into account. The properties of purely nucleonic np matter are studied as a function of the baryon density n_B and the asymmetry parameter α, as well as the properties of electrically neutral β-equilibrium npe μ matter as a function of the baryon density n_B. For different values of n_B and a, such characteristics of np matter as the energy per baryon, the specific energy owing to isospin asymmetry, the effective proton and neutron masses, and the specific binding energy, are determined. It is shown that the energy owing to the asymmetry for a fixed value of α is a monotonically increasing function of the baryon density n_B. For npem matter, the effective proton and neutron masses \({M}_{p}^{\left(eff\right)},{M}_{n}^{\left(eff\right)},\) the specific binding energy E_bind, the symmetry energy E_sym, the quantitative fraction of protons Y_p = n_p/n_B are studied, as well as the average meson fields \(\widetilde{\upsigma },\widetilde{\upomega },\widetilde{\updelta },\) and \(\widetilde{\uprho }\) as functions of the baryon density n_B.