Effective Hadron Masses and Effective Interactions in Nuclear Matter

Relations among effective hadron masses, effective interactions and equations of state are studied using a generalized mean-field theory that includes the implicit and explicit density dependence of the effective masses and couplings. We find that we can make the effective ω-meson mass smaller and the equation of state softer simultaneously if the ω-meson mean field is proportional to the baryon density. In this case, there is a simple and exact relation between the effective ω-meson mass and the effective ω-nucleon coupling. According to this relation, the effective ω-nucleon coupling automatically decreases if the effective ω-meson mass decreases. Consequently, the equation of state becomes softer. An attempt to incorporate the QCD sum-rule results into the hadron field theory is also made.