Etudes sur la matrice de mélange leptonique et sur la matière noire
Résumé
Neutrino oscillations, the baryon asymmetry and dark matter are important evidences of new physics beyond the Standard Model. Neutrino oscillations imply neutrino masses and a lepton mixing matrix that can contribute to flavour violating processes and CP violation at low energies, accessible to next experiments, and to the CP violation necessary for baryogenesis. Among the most interesting implications, is flavour violation in the lepton sector, but it has only been observed in neutrino oscillations. By analogy with quarks, it is then possible to deduce a principle of minimal flavour violation for leptons. Since such formulation is not straightforward in the lepton sector, we discuss dierent possibilities. Then we propose a definition which could be applied to various models and could help us in selecting between the possible neutrino mass generating mechanisms. Furthermore, if the seesaw mechanism describes neutrino masses, we can have a natural explanation to the baryon asymmetry of the universe with leptogenesis. In the context of leptogenesis including flavour effects, we demonstrate that the baryon asymmetry of the universe is insensitive to the low energy CP violating phases. This study is performed in the minimal extension of the Standard Model, with the introduction of 3 right-handed neutrinos and type-1 seesaw, only, and it is extended, in a following study, to the supersymmetric case. Since the seesaw parameter space is quite large, the numerical study is developed with the Markov Chain Monte Carlo method. In relation to dark matter, we study a scenario with very weakly coupled candidates and their production through the decay of a charged long-lived scalar particle. We compute the scalar particle number density, evaluating its gauge interactions, and compare it with Big-Bang Nucleosynthesis bounds. Then, we apply our results to the Minimal Supersymmetric Standard Model scenario with axino or gravitino as Lightest Supersymmetric Particle and stau or stop as Next to Lightest Supersymmetric Particle.
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