Shock wave and neutrino self-interaction effects upon neutrino flavor conversion in the supernovae environment

Since the discovery of the neutrino oscillation phenomenon by the Super-Kamiokande experiment and of the MSW effect as the solution of the solar neutrino deficit, the study of the neutrino propagation and of their flavor conversion in astrophysical environments is a very active field. This PhD thesis focuses upon flavor conversion phenomena of supernova neutrinos. In a first work, we performed the first complete calculation including the shock wave and the neutrino self-interaction to estimate the diffuse supernova neutrino background (DSNB) flux arriving on Earth. This neutrino flux comes from all the supernovae that exploded in the visible Universe. By varying the value of the third angle θ₁₃ of the mixing matrix U_MNSP, our numerical results have shown that the shock wave has a significant impact on the DSNB flux. At the same time, we have proposed a simplified model that accounts for the shock wave effects to be used in future calculations of the DSNB flux. The second work of this thesis is focused on the first exact analytical derivation of the matter Hamiltonian in the presence of the neutrino self-interaction. We have underlined, in the two flavors case, the important role of the Dirac phase β-bar appearing in the matter basis and established a condition on the elements of the flavor Hamiltonian for the onset of bipolar oscillations. In the third work, using the polarization vector formalism, we have identified a correspondence between the 'spectral split' and the magnetic resonance phenomena: the neutrino energies for which the magnetic resonance criteria are fulfilled undergo a flavor change at the location where the 'spectral split' occurs. A preliminary study of the three flavors case indicates us that the correspondence between the 'spectral split' and the magnetic resonance holds in this case as well. (author)