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tel-00450051, version 1 - 25 Jan 2010 namic density profile with shock waves. Indeed, such dynamic profiles can lead to forward and reverse shock responsible for new neutrino features such as phase effects or non-adiabatic high resonances. The aim of the third work has been to obtain a state of the art neutrino flux calculation, the first one including both the neutrino-neutrino interaction and a dynamic density profile with forward and reverse shocks. Such a code calculates the neutrino propagation through the supernova using wave functions ensuring that all relevant phase effects have been taken into account. Consequently, we have been able to predict, in the inverted hierarchy case, the number of positron events, associated to inverse β decay, from a galactic supernova explosion in a very realistic way. We have shown that a dip, consequence of the shock wave and of the self-interactions, should be seen in the positron signal from about 2 seconds after the bounce, during a few seconds, for a certain range of positron energies. Such a result looks particularly promising also in view of future large scale supernova neutrino observatories currently under study. Finally, as an application to our previous findings on δ effects, we have investigated the possible consequences of the CP-violating phase before neutrino decoupling in the Early Universe. The possible observables are the electron neutrino degeneracy parameter and consequently the neutron to proton ratio which plays a crucial role in BBN. Following a similar derivation obtained in the supernova context, we have been able to show under which conditions the CP-violating phase should have an impact on ξe. Indeed, if one takes into account the muon anti-muon pair interaction with neutrinos then, as for the one loop corrections in the supernova context, no factorization of δ out of the Hamiltonian is possible. Moreover, if we consider different initial degeneracy parameters for νµ and ντ, then we will also see δ effects on ξe. We are currently finishing to write a 3 flavour code using density matrices to quantify the effects induced by δ in such cosmological environment. The results of this PhD thesis, mainly turned on the effects of the CP-violating phase on the neutrino fluxes in dense matter, have allowed us to clearly identify under which conditions there can be CP violation effects in the astrophysical (core-collapse supernovae) and also in the cosmological (before BBN) contexts. Our results have numerous implications and applications. From the point of view of neutrino propagation, several improvements can be made. For example, one should perform demanding numerical calculations of the CP effects in the supernova environment with three-dimensional multi-angle and dynamic treatment of the neutrino fluxes, including eventually turbulence effects. Besides, to come to a definite statement concerning possible effects on the r-process much further work is still needed. With the obtained hindsight on this subject, one can think of direct applications of the analytic derivations and in particular, calculate precisely what could be the difference between the νµ and ντ fluxes at the neutrinosphere. Such differences could not only come from one loop corrections but also from Beyond Standard Model physics like Flavour Changing Neutral Current for in- 148
tel-00450051, version 1 - 25 Jan 2010 stance. Future discoveries, e.g. from LHC, could therefore imply effects in the supernova and cosmological (before BBN) contexts through CP-violation in the lepton sector. Let us hope that the new paths opened will lead to interesting discoveries and may be the key to some crucial problems related to astrophysical and cosmological neutrinos. 149
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