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Neutron-proton mass difference in a baryonic medium and the Nolen-Schiffer anomaly

Authors: M. Fiolhais, C. Christov, T. Neuber, M. Bergmann and K. Goeke

Ref.: Physics Letters B 269, 43-48 (1991)

Abstract: The neutron-proton mass difference Delta Mnp=Mn-Mp in a baryonic medium is evaluated in the framework of the Nambu-Jona-Lasinio model. It is demonstrated that Delta Mnp(varrho) increases with increasing medium density, varrho, a trend being opposite to the one required to explain the Nolen-Schiffer anomaly as suggested by Henley and Krein. In the same conceptual framework the quantity Mn(varrho n) - Mp(varrho p) is evaluated which takes into account that the valence orbits of the proton and the neutron are different. The calculations show that this quantity goes into the right direction, but the effect is an order of magnitude larger than needed to explain the Nolen-Schiffer anomaly.