Neutrino Properties Probed by Lepton Number Violating Processes

Fundamental properties of the neutrinos like their absolute mass, their character (are they Dirac or Majorana particles?), their mass hierarchy, the number of neutrino flavors, etc., are still unknown. Lepton Number Violating (LNV) processes are capable to decide on these issues. Since recently, the neutrinoless double beta decay was considered the only process able to distinguish between Dirac or Majorana neutrinos and to provide information about the mass scale of the electron neutrino. Now, the increase of the integrated luminosity at the LHC experiments makes feasible the study of LNV processes at high energy, as well. In this lecture I shall give a short review on these processes at low and high energies highlighting the motivation for their search.