Quantum many-body techniques for the description of spin-isospin excitations and beta-decay rates for the r process*

Modeling the r-process nucleosynthesis requires a huge amount of nuclear physics input, and in particular, the knowledge of beta-decay rates for thousands of neutron-rich nuclei. Due to their very short lifetimes, most of these nuclei are not accessible experimentally and astrophysical simulations thus heavily rely on theoretical methods, which should be as universal and reliable as possible.

In this context, microscopic methods based on the self-consistent mean field, such as the quasiparticle random phase approximation (QRPA), are good candidates as they are applicable to arbitrarily heavy nuclei at relatively low numerical cost. QRPA, however, suffers from a lack of correlations that typically leads to an imprecise description of the nuclear response, in particular the low-energy behavior, which determines beta decay. Extending this approach is thus crucial to improve the precision and reliability of the calculations and ultimately decrease the resulting uncertainties in the predictions of elemental abundances.

In this talk I will discuss how accounting for the coupling between nucleons and collective nuclear vibrations provides a way to include the relevant correlations needed to achieve this goal. I will present calculations of spin-isospin modes of excitations that can be compared to data, as well as new calculations of beta-decay rates of neutron-rich nuclei, focusing on those around neutron-shell closures which are of particular importance for the r-process. I will examine the impact of particle-vibration coupling on the rates, and the contribution of both Gamow-Teller and first-forbidden transitions.