Relativistic mean-field theory with the pion in finite nuclei

We study the possibility of the existence of a finite pion mean field in finite nuclei in the relativistic mean-field (RMF) theory. We are led to conjecture this existence by findings of the essential role of the pion in few-body systems and (p,n) experiments for spin-isospin excitations of medium and heavy nuclei. We carry out explicit calculations for various N=Z closed shell nuclei with a finite pion mean field in the RMF theory with the standard parameter set and pion-nucleon coupling in free space. We find that the finite pion mean field breaks the parity symmetry of the intrinsic single-particle states. We demonstrate the actual existence and elucidate the properties of the finite pion mean field, whose qualitative consequences for various observables are also briefly discussed. (author)