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.
Highlights
The neutrinoless double beta (0νββ) decays of atomic nuclei are of great experimental and theoretical interest due to their implications of physics beyond the standard model of electroweak interactions
It is obvious that the shape of the spectra depends sensitively on the value of gA but not as strongly as the transitions associated with the mother nuclei 113Cd and 115In, as shown in the figures of Haaranen et al [177]
The quenching of the weak axial-vector coupling strength, gA, is an important issue considering its impact on the detectability of the neutrinoless double beta decay
Summary
The neutrinoless double beta (0νββ) decays of atomic nuclei are of great experimental and theoretical interest due to their implications of physics beyond the standard model of electroweak interactions Since these processes occur in nuclei, nuclear-structure effects play an important role and they may affect considerably the decay rates. (e) A further important aspect can be added to the list, namely the uncertain value of the weak axial-vector coupling strength gA, leading to an effective value of gA in nuclear-model calculations. The weak vector and axial-vector coupling strengths gV and gA enter the theory when the hadronic current is renormalized at the nucleon level [29]. Since the vector bosons W± have large mass and propagate only a short distance, the hadronic current and the leptonic current can be considered to interact at a point-like weak-interaction vertex with an effective coupling strength GF, the Fermi constant. 100 MeV and the full expression (2) is active with slow decreasing trend of the coupling strengths according to Equation (5)
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