Abstract
Are neutrinos with definite masses Majorana or Dirac particles? This is one of the most fundamental problems of modern neutrino physics. The solution to this problem could be crucial for understanding the origin of small neutrino masses. We review here basic arguments in favor of the Majorana nature of massive neutrinos. The phenomenological theory of 0νββ-decay is briefly discussed and recent experimental data and sensitivity of future experiments are presented.
Highlights
The origin of small neutrino masses, discovered in neutrino oscillation experiments, is a major problem of modern neutrino physics
What is the character of the neutrino mass spectrum (Normal or Inverted Ordering?); What is the value of the CP phase δ?; How many neutrinos with definite masses νi exist in nature? Is the number of νi equal to the number of flavor neutrinos νl (l = e, μ, τ) or larger?; What is the nature of neutrinos with definite masses? Are they Majorana or Dirac particles?
The study of neutrinoless double β-decay of some even-even nuclei (0νββ-decay) is the most sensitive way which could allow us to discover the non conservation of the total lepton number L and to reveal the Majorana nature of neutrinos with definite masses
Summary
The origin of small neutrino masses, discovered in neutrino oscillation experiments, is a major problem of modern neutrino physics. If we assume that Standard Model neutrinos are two-component massless particles, in this case neutrino masses are generated by a new, beyond the SM mechanism. After spontaneous symmetry breaking this effective Lagrangian generates Majorana neutrinos with definite masses, three-neutrino mixing, and seesaw-type suppression of neutrino masses with respect to Standard Model masses of lepton and quarks. This is the simplest and most plausible, beyond the SM possibility to generate neutrino masses and mixing.. The study of neutrinoless double β-decay of some even-even nuclei (0νββ-decay) is the most sensitive way which could allow us to discover the non conservation of the total lepton number L and to reveal the Majorana nature of neutrinos with definite masses. The observation of the 0νββ-decay will allow the exclusion of this, apparently, artificial possibility
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