Elimination of the vacuum instability for finite nuclei in the relativistic sigma - omega model

The $\sigma$-$\omega$ model of nuclei is studied at leading order in the $1/N$ expansion thereby introducing the self consistent Hartree approximation, the Dirac sea corrections and the one fermion loop meson self energies in a unified way. For simplicity, the Dirac sea is further treated within a semiclassical expansion to all orders. The well-known Landau pole vacuum instability appearing in this kind of theories is removed by means of a scheme recently proposed in this context. The effect of such removal on the low momentum effective parameters of the model, relevant to describe nuclear matter and finite nuclei, is analyzed. The one fermion loop meson self energies are found to have a sizeable contribution to these parameters. However, such contribution turns out to come mostly from the Landau poles and is thus spurious. We conclude that the fermionic loop can only be introduced consistently in the $\sigma$-$\omega$ nuclear model if the Landau pole problem is dealt with properly.