Effects of the Dirac Sea on the Giant Monopole States

Abstract

Effects of the Dirac sea on the excitation energy of the giant monopole states are investigated in an analytic way within the $\sigma-\omega$ model. The excitation energy is determined by the relativistic Landau-Migdal parameters, $F_0$ and $F_1$. Their analytic expressions are derived in the relativistic random phase approximation(RRPA) without the Dirac sea, with the Pauli blocking terms and with the full Dirac sea. It is shown that in the RRPA based on the mean field approximation the Pauli blocking terms should be included in the configuration space, according to the relativistic Landau theory. In the renormalized RRPA, the incompressibility coefficient becomes negative, if N$\nbar$ excitations are neglected.