Neutrinoless double beta decay: 2015 review

The discovery of neutrino masses through the observation of oscillations boosted the importance of neutrinoless double beta decay (0 β β). In this paper, we review the main features of this process, underlining its key role from both the experimental and theoretical point of view. In particular, we contextualize the 0 β β in the panorama of lepton number violating processes, also assessing some possible particle physics mechanisms mediating the process. Since the 0 β β existence is correlated with neutrino masses, we also review the state of the art of the theoretical understanding of neutrino masses. In the final part, the status of current 0 β β experiments is presented and the prospects for the future hunt for 0 β β are discussed. Also, experimental data coming from cosmological surveys are considered and their impact on 0 β β expectations is examined.