The quenching of the axial-vector coupling constant $g_A$ in $\beta$-decay: joint effects from chiral two-body currents and many-body correlations

TL;DR

This paper presents a microscopic approach combining chiral two-body currents and many-body correlations to explain the quenching of the axial-vector coupling constant $g_A$ in nuclear beta decay, accurately reproducing experimental Gamow-Teller strengths.

Contribution

The study introduces a novel microscopic model that simultaneously incorporates chiral two-body currents and many-body correlations to explain $g_A$ quenching in beta decay.

Findings

The model reproduces experimental Gamow-Teller strengths without additional adjustments.

Quenching factors obtained range from approximately 0.73 to 0.80, aligning with empirical values.

Self-consistent calculations in three doubly magic nuclei demonstrate the combined effects of correlations and chiral currents.

Abstract

In nuclear $\beta$-decay calculations, the axial-vector coupling constant $g_A \approx 1.27$ usually needs to be quenched phenomenologically by a factor $q~\approx$ 0.75 to reproduce {the Gamow-Teller (GT) transition strengths}. We propose a novel approach to quench the GT {strength} of $\beta$-decay within the microscopic random phase approximation (RPA) plus particle-vibration coupling (PVC) approach, incorporating the contributions of two-body currents (TBC) derived from chiral effective field theory ($\chi$EFT). Self-consistent RPA+PVC calculations are performed in three doubly magic nuclei, $^{56}$Ni, $^{100}$Sn, and $^{132}$Sn, with various Skyrme energy density functionals, and the effect of TBC is evaluated by using the obtained many-body wavefunctions. A combined effects of the many-body correlations introduced by PVC and chiral TBC quench the GT strength and reproduce quantitatively experimental data without any additional adjustments. The extracted quenching factors $q$ by the present microscopic model lie in the range $\approx$ 0.73--0.80, which is quite close to the commonly adopted empirical value of $q \approx 0.75$.