In-medium proton-neutron mass difference and the systematics of the Nolen-Schiffer anomaly

We investigate a recent suggestion that the Nolen-Schiffer anomaly can be resolved if the in-medium proton-neutron mass difference is substantially changed from its free space value. In a number of hadronic models, such an effect is a natural consequence of partial chiral restoration in the nuclear medium. This suggestion is meaningful in the context of a local-density approximation, which has strong implications for the systematics of the Nolen-Schiffer anomaly over a range of nuclei. We show that such a mechanism predicts both noticeable shell effects and modest variations in the anomaly as the nuclear size is changed.

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