Ab initio calculations for shell evolution in proton-dripline nuclei

Shell evolution has been systematically investigated in neutron-rich isotopes, revealing many exotic properties such as the disappearance of traditional magic numbers and the emergence of new ones. However, research on proton-rich nuclei remains limited. In this study, we utilize ab initio valence-space in-medium similarity renormalization group approach using chiral effective field theory-derived interaction to explore shell evolution in the proton-dripline region. We first examine how the conventional shell closures at 8, 20, and 28 evolve from the stability line to the proton/neutron drip line, analyzing the average occupation, effective single-particle energy, and low-lying spectra. Our calculations reproduce the disappearance of N = 8, 20, and 28 magic numbers near 12 Be, 32 Mg, and 44 S, respectively. Additionally, we find that the Z = 8, 20, and 28 also vanish in the mirror nuclei of these isotopes, forming the Z = 8, 20, and 28 islands of inversion , respectively. Notably, the strength of the proton shell is weaker than that of the neutron shell, which is an indication of larger deformations in proton-rich nuclei than in their neutron-rich mirror counterparts. Furthermore, we investigate the observed new magic numbers 14, 16, 32, and 34, successfully reproducing the double magicity of 22,24 O and 52,54 Ca, which also persist in their respective mirror nuclei. However, significant isospin symmetry breaking is observed. For example, the 2 + excitation energy of 22 Si is approximately 800 keV lower than in its mirror nuclei, and the strength of the N = 32 shell closure is stronger than that of N = 34 subshell, a contrast that is reversed in their proton-rich counterparts.