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The one-QRPA method is used to describe simultaneously both double decay betamodes, giving special attention to the partial restoration of spin-isospinSU(4) symmetry. To implement this restoration and to fix the model parameters,we resort to the energetics of Gamow-Teller resonances and to the minima of thesingle $\beta^+$-decay strengths. This makes the theory predictive regardingthe $\beta\beta_{2\nu}$-decay, producing the $2\nu$ moments in $^{48}$Ca,$^{76}$Ge, $^{82}$Se, $^{96}$Zr, $^{100}$Mo, $^{128,130}$Te, and $^{150}$Nd,that are of the same order of magnitude as the experimental ones; however, theagreement with $\beta\beta_{2\nu}$ data is only modest. To includecontributions coming from induced nuclear weak currents, we extend the$\beta\beta_{0\nu}$-decay formalism employed previously in C. Barbero et. al,Nuc. Phys. A628, 170 (1998). The numerical results for the $\beta\beta_{0\nu}$moments in the above mentioned nuclei are similar to those obtained in othertheoretical studies although smaller on averag by $\sim 40\%$. We attributethis difference basically to the one-QRPA-method, employed here for the firsttime, instead of the currently used two-QRPA-method. The difference ispartially due to the way of carrying out the restoration of the spin-isospinsymmetry. It is hard to say which is the best way to make the restoration,since the $\beta\beta_{0\nu}$ moments are not experimentally measurable. Thenumerical uncertainties in the $\beta\beta$ moments, related with i) theirstrong dependence on the residual interaction in the p-p channel when evaluatedwithin the QRPA, and ii) lack of proper knowledge of single-particle energies,have been quantified. It is concluded that the partial restoration of the SU(4) symmetry is crucial in the description of the $\beta\beta$-decays,regardless of the nuclear model used.

Partial restoration of spin-isospin SU(4) Symmetry and the One-QRPA method in Double Beta Decay