The modified σ-ω model for relativistic nuclear matter

We have developed the modified σ-ω model. It includes the modified scalar and vector vertices expressed by the operators like the positive- and negative-energy projections and by two additional parameters. These vertices finally result in the effective density-dependent NNσ and NNω coupling constants. Comparing our results with the Dirac-Brueckner-Hartree-Fock (DBHF) calculations, the one-boson-exchange-model of NN force and the empirical value of the incompressibility, we can see that the two parameters should be nearly equal and that their values should be between 0.4 and 0.6. This favorable result is due to opposite effects by the modified scalar and vector vertices. At the saturation density, provided that values of the two parameters are 0.6, our result is almost equivalent to the DBHF result. The strengths of the potentials at all the densities and the energy per particle at the densities higher than the saturation point decrease, as the density-dependencies of the coupling constants become stronger. Consequently, it is found that the modified σ-ω model is able to reproduce the reasonable values of the coupling constants, potentials and incompressibility, and so may overcome the shortcomings of the original Walecka σ-ω model. (author)