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 sigma, omega, and rho mesons, and the isovector, Lorentz-scalar field of the delta-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 alpha, as well as the properties of electrically neutral beta-equilibrium npe mu 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 alpha is a monotonically increasing function of the baryon density n(B). For npem matter, the effective proton and neutron masses M-p((eff)), M-n((eff)), 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 (sigma) over tilde, (omega) over tilde, (delta) over tilde, and (rho) over tilde as functions of the baryon density n(B).