Microscopic origin of reflection-asymmetric nuclear shapes

TL;DR

This paper investigates the microscopic origins of reflection-asymmetric (pear-shaped) nuclear ground states, highlighting the role of specific multipole interactions, especially neutron-proton and isoscalar components, in inducing these shapes.

Contribution

It demonstrates that reflection-asymmetric nuclear shapes are primarily driven by odd-multipolarity neutron-proton and isoscalar interaction energies, advancing understanding of nuclear shape phenomena.

Findings

Reflection-asymmetric shapes are driven by neutron-proton (isoscalar) interaction energies.

The results align with the particle-vibration model emphasizing octupole-octupole interactions.

Large E3 polarizability is associated with octupole instability in nuclei.

Abstract

Background: The presence of nuclear ground states with stable reflection-asymmetric shapes is supported by rich experimental evidence. Theoretical surveys of odd-multipolarity deformations predict the existence of pear-shaped isotopes in several fairly localized regions of the nuclear landscape in the vicinity of near-lying single-particle shells with $\Delta\ell=\Delta j=3$. Purpose: We analyze the role of isoscalar, isovector, neutron-proton, neutron-neutron, and proton-proton multipole interaction energies in inducing the onset of reflection-asymmetric ground-state deformations. Methods: The calculations are performed in the framework of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory using two Skyrme energy density functionals and density-dependent pairing force. Results: We show that reflection-asymmetric ground-state shapes of atomic nuclei are driven by the odd-multipolarity neutron-proton (or isoscalar) part of the nuclear interaction energy. This result is consistent with the particle-vibration picture, in which the main driver of octupole instability is the isoscalar octupole-octupole interaction giving rise to large $E3$ polarizability.