Skyrme RPA for nuclear resonances: trouble with magnetic modes

TL;DR

This paper examines the differences between electric and magnetic nuclear excitations within Skyrme RPA calculations, highlighting challenges in modeling magnetic modes and suggesting the need for improved functionals.

Contribution

It identifies the limitations of current Skyrme functionals in accurately describing magnetic nuclear excitations and emphasizes the need for developments in the spin channel.

Findings

Landau-Migdal parameters explain electric transition success

Magnetic modes are not well described by existing Skyrme functionals

Further functional development is needed for magnetic excitations

Abstract

We discuss major differences between electric and magnetic excitations in nuclei appearing in self-consistent calculation based on Skyrme energy-density functionals. Tools of analysis are Landau-Migdal parameters for bulk properties and RPA for resonance modes of $^{208}$Pb as representative of finite nuclei. We show that the relation between the effective mass and the effective particle-hole interaction, well known in the Landau-Migdal theory, explains the success of self-consistent calculations of electric transitions in such approaches. This effect, however, does not automatically exist in the magnetic case. This calls for further developments of the Skyrme functional in the spin channel.