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 nu beta beta). 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 nu beta beta in the panorama of lepton number violating processes, also assessing some possible particle physics mechanisms mediating the process. Since the 0 nu beta beta existence is correlated with neutrino masses, we also review the state of the art of the theoretical understanding of neutrinomasses. In the final part, the status of current 0 nu beta beta experiments is presented and the prospects for the future hunt for 0 nu beta beta are discussed. Also, experimental data coming from cosmological surveys are considered and their impact on 0 nu beta beta expectations is examined.