<i>Ab initio</i> study of shell evolution in neutron-rich Si, S, Ar, and Ca isotopes near <i>N</i> = 32 and 34*

Abstract Shell evolution is crucial for understanding nuclear structures across the nuclear chart. In this work, we employed the ab initio valence space in-medium similarity renormalization group with chiral nucleon-nucleon and three-nucleon interactions to study neutron-rich Si, S, Ar, and Ca isotopes, particularly focusing on nuclei near . We systematically analyzed both neutron and proton shell evolutions by examining the excitation energies of the first states and the effective single-particle energies. Our calculations show that the sub-shell gradually weakens as protons are removed from the doubly magic nucleus , eventually disappearing in . Conversely, the strength of the sub-shell is enhanced with the removal of protons from . Furthermore, our results indicate the existence of the proton sub-shell in neutron-rich Si isotopes. These findings suggest that is a doubly magic nucleus, with the excitation energy of the first state around 2.49 MeV, which is approximately 400 keV higher than that of . This value is comparable to those of other well-known exotic doubly magic nuclei, such as and , which is of great interest for further experiments at RIB facilities. In addition, we predicted the low-lying spectra of neutron-rich Si, S, and Ar isotopes, providing new insights for future experiments.