Etudes des proprietes des neutrinos dans les contextes ...

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