Effect of chiral constraints on dense nuclear matter

We first discuss calculations in the Nambu-Jona-Lasinio model which show that the mass of the σ-meson, mσ, decreases with increasing density at the same rate as nucleon effective mass mN*, i.e. mσ*(ρ)/mσ=mN*/mN. We next discuss linear resonse theory in which Δ-particle, nucleon-hole insertions are put into pion lines; then masses of all the mesons seem to decrease with increasing density. To the extent that all of the masses scale in the same way, the common scale can be taken out of the hamiltonian, giving a new hamiltonian which involves only vacuum masses. The nucleon effective mass is calculated in the Dirac-Brueckner Hartree-Fock formalism, with inclusion of nucleon one-loop terms. The latter tend to keep mN*/mN large, ∝0.9. Finally, a full DBHF calculation is carried out, including the nucleon one-loop term and density dependent meson masses. With inclusion of the latter, conventional mechanisms in nuclear physics for saturation disappear and a density dependent two loop term ΔUσ(ρ) must be introduced. We motivate its introduction by empirical as well as formal arguments. In the discussion it is pointed out that the scaled meson masses can be considered, for a convenient density, as renormalization points. (orig.)