Collective excitations involving spin and isospin degrees of freedom

• Published in: The European Physical Journal A
• Main Authors: Sagawa H., Colò Gianluca., Roca-Maza X., Niu Y.
• Other Authors: H. Sagawa, G. Colò, X. Roca-Maza, Y. Niu
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2019
• Subjects: Settore FIS/04 - Fisica Nucleare e Subnucleare; sami
• Online Access: http://hdl.handle.net/2434/774856; https://doi.org/10.1140/epja/i2019-12923-y

In this paper, we discuss some new important developments in the study of isobaric analog states (IAS) and Gamow-Teller resonances (GTR). In the case of the IAS, we have shown the importance of taking into account charge symmetry breaking (CSB) and charge independence breaking (CIB) forces, in order to reconcile the reproduction of the IAS energy in 208Pb with the reproduction of some very basic observables like the neutron skin which, in turn, is strongly correlated with the density dependence of the symmetry energy. Isospin symmetry breaking terms can increase the energy of the IAS associated with Skyrme EDFs that produce a reasonable value of the neutron skin. In particular, this has been shown in the case of the SAMi functional. The GTR has a large damping width and its strength is experimentally found to be quenched with respect to standard RPA calculations. We have revised the PVC model for the width of giant resonances using the Skyrme force consistently for RPA (QRPA) and (quasi-)particle-vibration couplings (PVC or QPVC) calculations. We apply this model to the study of the GTR both in magic and open-shell nuclei. The results are in very good agreement with the experimental findings. The remaining discrepancies point to the necessity of fine tuning of the spin, spin-isospin, and spin-orbit terms in the existing EDFs. Some detailed formulas of CSB and CIB energy densities are given in the appendix.