Relativistic mean field theory with pion field for finite nuclei

A new framework, which is based on the relativistic mean field (RMF) theory with the inclusion of the pion on the same footing as other mesons, is developed. In the RMF theory, which is now widely used to study nuclear structure with great success, the pion is not usually treated directly and, therefore, it is an important subject to study the pion in the relativistic mean field model in which all the meson degrees of freedom including the pion are explicitly treated. The pseudoscalar and isovector characters of the pion axe not easy to treat in a conventional mean field model, where the parity and the charge symmetries of single-particle states are usually assumed. In this case, the pion cannot be exchanged by single-particle states, because it breaks these symmetries. The new idea to attack the problem of the pion is to break the parity and the charge symmetries of single-particle states. The pion can be exchanged between the symmetry-broken single-particle states as the other mesons. The new framework is applied to various N = Z nuclei and the large effect of the pion on these nuclei are found.