Mirror and triplet energy differences in sd -shell nuclei using microscopic interactions with isospin-symmetry breaking effects

Abstract Starting from an isospin-symmetric microscopic interaction of Shin et al. [Phys. Rev. C 110, 034306 (2024)], we developed two isospin symmetry breaking (ISB) shell-model interactions by adding Coulomb interaction, as well as charge-symmetry breaking (CSB) and charge-independence breaking (CIB) components from the Argonne v18 (Av18) interaction at two different radial cutoffs, rc = 0.55 and 0.70 fm. With additional modifications to the proton single-particle energies, we then employed these interactions to calculate the Coulomb displacement energies (CDEs) and triplet displacement energies (TDEs) of the isobaric multiplet masses for nuclei with |Tz| = 1/2 and T = 1 across the sd-shell to test their validity and applicability, and compared with the USDCm interaction. We found that both ISB interactions show important roles of the CSB and CIB components in the CDEs and TDEs. In addition, we investigated mirror energy differences (MEDs) in the low-energy spectra of nuclei around A = 20, and triplet energy differences (TEDs) in the A = 18 and 22 systems. They are generally well described by the ISB interactions, although some discrepancies remain. Furthermore, the calculated E2 transition strengths obtained with the ISB interactions are shown to be in good agreement with experimental data, indicating small ISB effects in these transitions. Overall, both the ISB interactions provide a consistent and physically motivated framework for describing ISB effects, while the phenomenological USDCm interaction achieves closer agreement with experiment due to a larger number of adjustable parameters.