Value of the axial-vector coupling strength in $\beta$ and $\beta\beta$ decays: A review

TL;DR

This review discusses the quenching of the axial-vector coupling strength $g_A$ in nuclear $eta$ and double-$eta$ decays, analyzing theoretical models, experimental data, and implications for future measurements.

Contribution

It provides a comprehensive overview of the historical and current understanding of $g_A$ quenching, integrating different many-body methods and experimental insights.

Findings

Separation of nuclear-medium and many-body effects on $g_A$ quenching

Comparison of theoretical models with experimental data

Identification of key measurements for future research

Abstract

In this review the quenching of the weak axial-vector coupling strength, $g_{\rm A}$, is discussed in nuclear $\beta$ and double-$\beta$ decays. On one hand, the nuclear-medium and nuclear many-body effects are separated, and on the other hand the quenching is discussed from the points of view of different many-body methods and different $\beta$-decay and double-$\beta$-decay processes. Both the historical background and the present status are reviewed and contrasted against each other. The theoretical considerations are tied to performed and planned measurements, and possible new measurements are urged, whenever relevant and doable. Relation of the quenching problem to the measurements of charge-exchange reactions and muon-capture rates is pointed out.