Environment Dependence of the Neutron - Proton Mass Difference

Abstract An increase in the size of the nucleon inside nuclear matter, suggested as an explanation of the EMC effect, can lead to an A -dependent change in the neutron-proton mass difference. We examine this effect in several versions of the quark model, and discuss its possible relevance to the Nolen-Schiffer anomaly in the mass differences of mirror nuclei.