We discuss major differences between electric and magnetic excitations in nuclei appearing in self-consistent calculations based on Skyrme energy-density functionals (EDFs). For this we calculate collective low- and high-lying electric and magnetic excitations in Pb208 within a self-consistent Skyrme EDF approach using the random-phase approximation (RPA) and a more sophisticated particle-hole plus phonon-coupling model, coined the time-blocking approximation (TBA). Tools of analysis are Landau-Migdal parameters for bulk properties and the RPA and TBA results for finite nuclei. We show that the interplay between the effective mass and the effective particle-hole interaction, well known in the Landau-Migdal theory, renders the final results rather independent of the effective mass by virtue of the “backflow effect.” It explains the success of self-consistent calculations of electric transitions in such approaches. This effect, however, is absent in the magnetic case and leads to higher fluctuations in the results. It calls for further developments of the Skyrme functional in the spin channel.

中文翻译：

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核共振的广义 Skyrme 随机相位近似：电和磁模式的不同趋势

我们讨论了基于 Skyrme 能量密度函数 (EDF) 的自洽计算中出现的原子核中电激发和磁激发之间的主要区别。为此，我们使用随机相位近似 (RPA) 和更复杂的粒子孔加声子耦合模型，在自洽 Skyrme EDF 方法中计算 Pb208 中的集体低位和高位电和磁激发，创造了时间-阻塞近似（TBA）。分析工具是体积特性的 Landau-Migdal 参数以及有限原子核的 RPA 和 TBA 结果。我们表明，Landau-Migdal 理论中众所周知的有效质量和有效粒子-空穴相互作用之间的相互作用，通过“回流效应”使最终结果与有效质量无关。”它解释了在这种方法中自洽计算电跃迁的成功之处。然而，这种效应在磁性情况下不存在，并导致结果的更大波动。它要求进一步开发自旋通道中的 Skyrme 功能。