Stellar electron capture rates based on finite temperature relativistic quasiparticle random-phase approximation

TL;DR

This paper develops a relativistic framework to calculate stellar electron capture rates on nuclei, incorporating finite temperature and pairing effects, which significantly influence the rates crucial for supernova modeling.

Contribution

It introduces a finite temperature relativistic quasiparticle random-phase approximation including pairing, providing more accurate electron capture rates in stellar environments.

Findings

Pairing correlations unblock certain nuclear transitions.

Finite temperature and pairing effects can double or increase electron capture rates.

Significant impact on electron capture rates for ${}^{44}$Ti and ${}^{56}$Fe.

Abstract

The electron capture process plays an important role in the evolution of the core collapse of a massive star that precedes the supernova explosion. In this study, the electron capture on nuclei in stellar environment is described in the relativistic energy density functional framework, including both the finite temperature and nuclear pairing effects. Relevant nuclear transitions $J^\pi = 0^\pm, 1^\pm, 2^\pm$ are calculated using the finite temperature proton-neutron quasiparticle random phase approximation with the density-dependent meson-exchange effective interaction DD-ME2. The pairing and temperature effects are investigated in the Gamow-Teller transition strength as well as the electron capture cross sections and rates for ${}^{44}$Ti and ${}^{56}$Fe in stellar environment. It is found that the pairing correlations establish an additional unblocking mechanism similar to the finite temperature effects, that can allow otherwise blocked single-particle transitions. Inclusion of pairing correlations at finite temperature can significantly alter the electron capture cross sections, even up to a factor of two for ${}^{44}$Ti, while for the same nucleus electron capture rates can increase by more than one order of magnitude. We conclude that for the complete description of electron capture on nuclei both pairing and temperature effects must be taken into account.