| The mass of a nucleon in a nucleus is studied using a model for a nucleon current with a pion cloud component. The method of QCD sum rules is used to determine the mass shifts for nucleons to first order in nuclear density in 16O and 40Ca, with the pion propagator determined by an optical potential for pion-nucleus scattering. Mass shifts due to the pionic contributions range from negligible in oxygen to -100 MeV in calcium at central nuclear density, with larger shifts in the nuclear surface. The consistency of this model with chiral perturbation theory is demonstrated. |
