Skyrme-Rpa Description of Spin-Flip M1 Giant Resonance

TL;DR

This study uses the Skyrme-RPA framework with various parameterizations to analyze the spin-flip M1 giant resonance across different nuclei, highlighting the importance of spin densities and the need for tensor interactions.

Contribution

It provides a comprehensive RPA analysis of the spin-flip M1 resonance with multiple Skyrme functionals, identifying limitations and suggesting improvements involving tensor and isovector spin-orbit interactions.

Findings

Spin densities are crucial for the collective shift.

None of the Skyrme parameterizations fully match experimental data.

Relative proton and neutron spin-orbit splitting is a key issue.

Abstract

The spin-flip M1 giant resonance is explored in the framework of Random Phase Approximation on the basis of the Skyrme energy functional. A representative set of eight Skyrme parameterizations (SkT6, SkM*, SLy6, SG2, SkO, SkO', SkI4, and SV-bas) is used. Light and heavy, spherical and deformed nuclei ($^{48}$Ca, $^{158}$Gd, $^{208}$Pb, and $^{238}$U) are considered. The calculations show that spin densities play a crucial role in forming the collective shift in the spectrum. The interplay of the collective shift and spin-orbit splitting determines the quality of the description. None of the considered Skyrme parameterizations is able to describe simultaneously the M1 strength distribution in closed-shell and open-shell nuclei. It is found that the problem lies in the relative positions of proton and neutron spin-orbit splitting. Necessity to involve the tensor and isovector spin-orbit interaction is called for.