Introduction to Double Beta Decay

While the neutrino oscillation experiments have measured non-zero square mass differences between neutrino flavors, the double beta decay is the most sensitive process to the absolute mass of the neutrinos and the only that can distinguish whether neutrino is a Dirac or a Majorana particle. These are a few but not the only reasons that many efforts, both theoretically and experimentally, are dedicated to the study of this process. In this lecture I'll give a short introduction to the double beta decay process. Different decay modes and mechanisms, a short history, decay rates and extraction of the neutrino mass parameter are presented.