The Majorana neutrino hypothesis

Once Majorana had returned from abroad, where he met several other important personalities including Bloch, Bohr and Weisskopf, he did not publish any papers for several years. But his research activity during this period, which focused mainly on field theory and quantum electrodynamics, is well testified by a number of unpublished scientific notes that are currently being studied.

In 1937, however, probably after being invited by Fermi to compete for a full professorship, Majorana published what was to become his most famous paper [9]: “Symmetric theory of electrons and positrons”, in which he introduced the so-called Majorana neutrino hypothesis.

This hypothesis was revolutionary because it argued that the antimatter partner of a given matter particle could be the particle itself. This was in direct contradiction to what Dirac had successfully assumed in order to solve the problem of negative energy states in Quantum Field Theory (i.e. the existence of the positron). With unprecedented farsightedness Majorana suggested that the neutrino, which had just been postulated by Pauli and Fermi to explain puzzling features of radioactive beta decay, could be such a particle. This would make the neutrino unique among the elementary particles and, moreover, enable it to have mass. Today many experiments are still devoted to detect these peculiar properties, which include the phenomenon of neutrino oscillations.

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