After almost 100 years since its birth, the neutrino is still the
less understood particle of the Standard Model, the established theory
of particles and fields. Neutrinos are the most abundant massive
particles of the universe (as far as we know) and they are emitted
copiously by stars, nuclear reactor, particle accelerators, the Earth
and even the human body, but despite many recent discoveries they remain
very mysterious on several aspects. The so called Neutrino-less Double
Beta decay, a very rare radioactive decay of some nuclei, may, despite
its name, offer the opportunity to uncover the main mystery about
neutrinos, namely if they behave like the other spin ½ particles of the
Standard Model or, uniquely, they behave as predicted by Ettore Majorana
in the middle 30s, when the brilliant Italian theoretician developed a
theory of neutrinos as possible alternative with that developed by Paul
Dirac. While it is clear that charged particles must follow Dirac
theory, the Majorana option is still perfectly valid for neutral
particles such as neutrinos. The seminar will go through neutrino
properties and history and finally describe how neutrino-less double
beta decay may teach us if Ettore was right or wrong.