Nuclear matrix elements for neutrinoless double-beta decay and double-electron capture

Abstract

A new generation of neutrinoless double-beta decay (0νββ-decay) experiments with improved sensitivity is currently being designed and under construction. They will probe the inverted hierarchy region of the neutrino mass pattern. There is also a revived interest in the resonant neutrinoless double-electron capture (0νECEC), which also has the potential to probe lepton number conservation and to investigate the neutrino nature and mass scale. The primary concerns are the nuclear matrix elements. Clearly, the accuracy of the determination of the effective Majorana neutrino mass from the measured 0νββ-decay half-life is mainly determined by our knowledge of the nuclear matrix elements. We review recent progress achieved in the calculation of 0νββ and 0νECEC nuclear matrix elements within the quasiparticle random phase approximation. A considered self-consistent approach allows us to derive the pairing, residual interactions and the two-nucleon short-range correlations from the same modern realistic nucleon–nucleon potentials. The effect of nuclear deformation is taken into account. The possibility of evaluating 0νββ-decay matrix elements phenomenologically is discussed.