Neutron-Proton Mass Difference in Nuclear Matter and in Finite Nuclei and the Nolen-Schiffer Anomaly

TL;DR

This paper investigates how the neutron-proton mass difference varies in nuclear matter and finite nuclei using a medium-modified Skyrme model, addressing the Nolen-Schiffer anomaly and the role of effective nucleon mass.

Contribution

It introduces a medium-modified Skyrme model with isospin-breaking effects and pion optical potentials to study neutron-proton mass differences in nuclear environments.

Findings

Neutron-proton mass difference mainly driven by strong interaction component.

Mass difference decreases significantly in neutron-rich matter.

Constraints on nucleon effective mass modifications from mirror nuclei properties.

Abstract

The neutron-proton mass difference in (isospin asymmetric) nuclear matter and finite nuclei is studied in the framework of a medium-modified Skyrme model. The proposed effective Lagrangian incorporates both the medium influence of the surrounding nuclear environment on the single nucleon properties and an explicit isospin-breaking effect in the mesonic sector. Energy-dependent charged and neutral pion optical potentials in the s- and p-wave channels are included as well. The present approach predicts that the neutron-proton mass difference is mainly dictated by its strong part and that it markedly decreases in neutron matter. Furthermore, the possible interplay between the effective nucleon mass in finite nuclei and the Nolen-Schiffer anomaly is discussed. In particular, we find that a correct description of the properties of mirror nuclei leads to a stringent restriction of possible modifications of the nucleon's effective mass in nuclei.