Theoretical News from Neutrinoless Double Beta Decay

Neutrinoless double beta decay is a very sensitive experimental probe for physics beyond the Standard Model. In fact, this process is the only known possibility to ascertain in the foreseeable future whether the neutrino is a Dirac or a Majorana particle. Most theoretical results on this subject, however, have been known for many years. In the advent of the next generation of experiments, it is worthwhile to reexamine old results and provide some new theoretical contributions. This thesis deals with various topics related to neutrinoless double beta decay. In particular, we focus on a discussion of the famous Schechter–Valle (or Black Box) theorem, as well as on a realization of neutrinoless double beta decay in universal extra dimensions, which has not been considered in the literature so far. We find that the Schechter–Valle theorem, although valid, is of merely academic interest, as it generates a neutrino mass which is many orders of magnitude smaller than the one expected. Concerning universal extra dimensions, we are able to give a new bound on their size, which is slightly weaker but complementary to the existing constraints from electroweak precision data. Next generation experiments are expected to improve upon the bounds we obtain