Effective value of gA in β and ββ decays

Abstract

Effective value of the weak axial-vector coupling strength, g A , in nuclear β and ββ (double beta) decays is discussed. Both Gamow-Teller and first-forbidden β decays are included in the analyses. Quenching of g A in β and two-neutrino ββ decays is reviewed and impact of this quenching on neutrinoless ββ decays is addressed. New measurements of β spectra of first-forbidden non-unique β decays are encouraged, to learn about the mesonic enhancement of the weak axial charge in these decays.