Lepton number violating new physics and neutrinoless double beta decay

Neutrinoless double beta decay (0νββ) is a very promising experimental test for lepton number violation. Moreover, a strong connection between this decay and the phenomenon of neutrino masses exists. We will discuss the relation between 0νββ and Majorana neutrino masses established by the Schechter–Valle theorem in a quantitative way and find that only a negligibly tiny Majorana mass contribution is guaranteed. Additionally, we will discuss lepton number violation and lepton flavor violation in the colored seesaw scenario. This model generates neutrino masses at the one-loop level, and it provides a direct and an indirect contribution to 0νββ, both of which may be the dominant one.