# Relativistic approach to nuclear spin-isospin excitations including quasiparticle-vibration coupling

## TL;DR

This paper develops a relativistic quasiparticle approach including vibrational coupling to improve the modeling of nuclear spin-isospin excitations, with implications for beta decay and nuclear response accuracy.

## Contribution

It introduces the pn-RQTBA method that incorporates quasiparticle-vibration coupling into the relativistic framework, enhancing the description of nuclear excitations.

## Key findings

- Fragmentation of Gamow-Teller strength improves agreement with experiments.
- Vibrational coupling affects beta-decay half-lives and strength quenching.
- Dynamical effects are significant in both stable and exotic nuclei.

## Abstract

The spin-isospin response of stable and exotic nuclei is investigated in the framework of the proton-neutron relativistic quasiparticle time-blocking approximation (pn-RQTBA). Based on the Covariant Density Functional Theory, this method extends the proton-neutron Relativistic Quasiparticle Random-Phase Approximation (pn-RQRPA) by including the coupling between single quasiparticles and collective nuclear vibrations. In the charge-exchange channel, this coupling generates a time-dependent effective interaction between proton and neutron quasiparticles. The particle-hole component of this interaction adds to the static pion and rho-meson exchange, while the particle-particle component provides a microscopic and consistent proton-neutron pairing interaction. We find that such dynamical effects induce fragmentation and spreading of the Gamow-Teller transition strength which are important for a better agreement with the experimental measurements and for an accurate description of $\beta$-decay rates. The new developments include the coupling of single nucleons to isospin-flip vibrations in doubly-magic nuclei. We find that these phonons can have a non-negligible effect on $\beta$-decay half-lives and "quenching" of the strength.