Effective hadron masses and effective interactions in nuclear matter

Relations among the effective hadron masses and the effective interactions in nuclear matter are studied by using the generalized relativistic mean field theory. We found that we can make the effective omega-meson mass smaller and the equation of state softer if we require that the omega-meson mean field is proportional to the baryon density. In this case, there is a simple and exact relation between the effective omega-meson mass and the effective omega-nucleon coupling. Because of this relation, the effective omega-nucleon coupling automatically decreases if the effective omega-meson mass decreases. Consequently, the equation of state becomes softer. A trial to embed the QCD sum-rule results into the hadron field theory is also shown.