Mixed mode positron double beta decay: comparison with β-β- and future perspective

It is noted that at least two experiments on double beta decay should provide the independent verification of neutrinoless double beta decay. Two mechanisms beyond standard model: neutrino Majorana mass and right handed currents are expected to be most dominant ones. The perspective of mixed mode positron double beta decay (β+/EC) and β-β- cases along with the prospects of different nuclei as best candidates for 0ν ββ decay experiments are discussed. (author)