Prof. Dr. Frank Deppisch

The nature of neutrinos and the mechanism of generating their tiny masses are among the most important unknowns in fundamental physics. Being the only electrically neutral fermions in the Standard Model, neutrinos can be of Majorana nature, i.e., particle and antiparticle are indistinguishable. As such, any U(1) quantum number carried by a Majorana fermion will be violated and in the context of the Standard Model, Majorana neutrinos will break total lepton number, an otherwise accidental global symmetry. I will discuss scenarios beyond the Standard Model where Majorana neutrinos are realized, as well as scenarios that incorporate so-called quasi-Dirac Majorana states. As the most important probe of Majorana neutrinos, I will focus on neutrinoless double beta decay as the crucial signature, and I will discuss the latest theoretical and experimental developments.