The islands of shape coexistence within the Elliott and the proxy-SU(3) Models

TL;DR

This paper introduces a dual-shell mechanism explaining shape coexistence in nuclei across all mass regions, based on the interplay between Elliott SU(3) and proxy-SU(3) symmetries, predicting specific candidate nuclei without free parameters.

Contribution

It proposes a novel dual-shell mechanism for nuclear shape coexistence involving interchange between SO-like and HO shells within Elliott and proxy-SU(3) symmetries, predicting candidate nuclei across all mass regions.

Findings

Shape coexistence occurs in specific nuclear islands predicted by the model.

In light nuclei, nucleons flip shells, leading to shape coexistence and inversion.

In medium and heavy nuclei, shell merging unifies different shell types, facilitating coexistence.

Abstract

A novel dual-shell mechanism for the phenomenon of shape coexistence in nuclei within the Elliott SU(3) and the proxy-SU(3) symmetry is proposed for all mass regions. It is supposed, that shape coexistence is activated by large quadrupole-quadrupole interaction and involves the interchange among the spin-orbit (SO) like shells within nucleon numbers 6-14, 14-28, 28-50, 50-82, 82-126, 126-184, which are being described by the proxy-SU(3) symmetry, and the harmonic oscillator (HO) shells within nucleon numbers 2-8, 8-20, 20-40, 40-70, 70-112, 112-168 of the Elliott SU(3) symmetry. The outcome is, that shape coexistence may occur in certain islands on the nuclear map. The dual-shell mechanism predicts without any free parameters, that nuclei with proton number (Z) or neutron number (N) between 7-8, 17-20, 34-40, 59-70, 96-112, 146-168 are possible candidates for shape coexistence. In the light nuclei the nucleons flip from the HO shell to the neighboring SO-like shell, which means, that particle excitations occur. For this mass region, the predicted islands of shape coexistence, coincide with the islands of inversion. But in medium mass and heavy nuclei, in which the nucleons inhabit the SO-like shells, shape coexistence is accompanied by a merging of the SO-like shell with the open HO shell. The shell merging can be accomplished by the outer product of the SU(3) irreps of the two shells and represents the unification of the HO shell with the SO-like shell.