Dipole response in neutron-rich nuclei with new Skyrme interactions

TL;DR

This study examines the dipole response of neutron-rich nuclei using new Skyrme interactions, revealing significant isoscalar/isovector mixing influenced by the symmetry energy slope and neutron skin thickness.

Contribution

It introduces the use of SAMi-J Skyrme interactions to analyze dipole responses, highlighting the impact of symmetry energy slope on mode mixing in neutron-rich nuclei.

Findings

Isoscalar/isovector mixing increases with symmetry energy slope L.

Low-energy isovector strength mainly arises from isoscalar-like modes.

Mixing effects correlate with neutron skin extension.

Abstract

We investigate the isoscalar and isovector E1 response of neutron-rich nuclei, within a semi-classical transport model employing effective interactions for the nuclear mean-field. In particular, we adopt the recently introduced SAMi-J Skyrme interactions, whose parameters are specifically tuned to improve the description of spin-isospin properties of nuclei. Our analysis evidences a relevant degree of isoscalar/isovector mixing of the collective excitations developing in neutron-rich systems. Focusing on the low-lying strength emerging in the isovector response, we show that this energy region essentially corresponds to the excitation of isoscalar-like modes, which also contribute to the isovector response owing to their mixed character. Considering effective interactions which mostly differ in the isovector channels, we observe that these mixing effects increase with the slope L of the symmetry energy at saturation density, leading to a larger strength in the low-energy region of the isovector response. This result appears connected to the increase, with L, of the neutron/proton asymmetry at the surface of the considered nuclei, i.e., to the extension of the neutron skin.