Nuclear Symmetry Energy from a Relativistic Mean Field Theory

We discuss the density dependence and coupling-constant dependence of the nuclear symmetry energy in the relativistic mean field approximation of the σ?ω?ρ model. An extremely stiff density dependence of symmetry energy is obtained. At the same time, we find that the coupling constants g_σ and g_ω have greater effect on the nuclear symmetry energy than the self-coupling constants c and d. In particular, g_ω and g_σ determine the slope L and curvature K_sym of nuclear symmetry energy at saturation density, respectively.