Effective axial-vector strength within proton-neutron deformed quasiparticle random-phase approximation

We use the available experimental Gamow-Teller β− and β+/EC (electron-capture) decay rates between 0+ and 1+ ground states in neighboring even-even and odd-odd nuclei, combined with 2νββ half-lives, to analyze the influence of the nuclear environment on the weak axial-vector strength gA. For this purpose, the proton-neutron deformed quasiparticle random-phase approximation (pn-dQRPA), with schematic dipole residual interaction is employed. The Hamiltonian contains particle-hole (ph) and particle-particle (pp) channels with mass-dependent strengths. In deriving the equations of motion we use a self-consistent procedure in terms of a single-particle basis with projected angular momentum provided by the diagonalization of a spherical mean field plus the quadrupole-quadrupole interaction. Our analysis evidenced a quenched average effective value ⟨gA⟩ ≈ 0.7 with a root-mean-square deviation of σ ≈ 0.3 for transitions from even-even emitters and σ ≈ 0.6 for transitions from odd-odd emitters.