Preponderance of triaxial shapes in atomic nuclei predicted by the proxy-SU(3) symmetry

TL;DR

The paper predicts widespread triaxial shapes in atomic nuclei using the proxy-SU(3) symmetry, supported by empirical data and comparisons with advanced shell model calculations, revealing new insights into nuclear shape phenomena.

Contribution

It introduces a parameter-free prediction of nuclear triaxiality based on proxy-SU(3) symmetry, linking theoretical models with experimental data across the nuclear chart.

Findings

Substantial triaxiality predicted across many nuclei.

Empirical data supports the predicted nuclear shape regions.

Good agreement with Monte Carlo shell model calculations.

Abstract

The proxy-SU(3) symmetry predicts, in a parameter-free way, based only on the Pauli principle and the short-range nature of the nucleon-nucleon interaction, non-vanishing values of the collective variable gamma almost everywhere across the nuclear chart. Substantial triaxiality with gamma between 15 and 45 degrees is proved to be expected along horizontal and vertical stripes on the nuclear chart, covering the nucleon numbers 22-26, 34-48, 74-80, 116-124, 172-182. Empirical support for these stripes is found by collecting all even-even nuclei for which the first two excited 2+ states are known, along with the B(E2)s connecting them, as well as the second 2+ state to the ground state. The stripes are related to regions in which oblate SU(3) irreducible representations appear, bearing similarity to the appearance of triaxiality within the SU(3)* dynamical symmetry of the interacting boson model-2. Detailed comparisons of the proxy-SU(3) predictions to the data and to predictions by state-of-the-art Monte Carlo shell model calculations for deformed N=94, 96, 98 isotones in the rare earth region show good overall agreement, with the exception of Z=70 and N=94, which correspond to fully symmetric proxy-SU(3) irreps, suggesting that the latter are an artifact of the method which can be amended by considering the influence of the neighboring irreps.