Nuclear response theory for spin-isospin excitations in a relativistic quasiparticle-phonon coupling framework

Abstract

Abstract.A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and ρ-meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to previously developed relativistic quasiparticle time blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and applied to Gamow-Teller resonance in a chain of neutron-rich Nickel isotopes 68−78 Ni. A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.PACS. 21.60.Jz Nuclear Density Functional Theory and extensions (includes Hartree-Fock and randomphase approximations) -23.40.-s beta-decay; double beta-decay; electron and muon capture -21.10.Tg Lifetimes, widths

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“…[36] where results for the giant dipole resonance (GDR) in 120 Sn have been presented). This model has also been applied for the study of the GT response and the β-decay half-lives in Ni isotopes [37]. While the relativistic model is similar in spirit to the present one, we stress again that our goal is to address in detail the microscopic mechanisms related to quasi-particle-vibration coupling and, to some extent, also to IS pairing.…”

Quasiparticle-vibration coupling effects on nuclear transitions of astrophysical interest

“…According to the formalism of the relativistic quasiparticle time-blocking approximation [3,5] we solve the Bethe-Salpeter equation (BSE) for the response function in the corresponding channels. In the like-particle case, the final BSE reads [3] …”

Electric dipole response of neutron-rich calcium isotopes in relativistic quasiparticle time blocking approximation

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