Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
ABSTRACT
The neutrino oscillation phenomenon was discovered in 1998 by the Super-
Kamiokande experiment, 11 years after the first observation of neutrinos from a
supernova (SN1987A). Thus, this field has enormously developed over the last
ten years. The subject of this thesis is to study, in the astrophysical and cosmological
contexts, two unknown neutrino properties: the CP violation and the
third mixing angle of the MNSP matrix. We have shown analytically, for the
first time, the conditions under which there can be effects of the CP phase on
the neutrino fluxes in the star and the electron fraction, which is a key observable
of the r-process. The numerical calculations, including matter coupling and
the non-linear neutrino-neutrino interaction, have shown effects of several percents
in the star and smaller effects in an observatory. Then we have studied
the consequences of the third mixing angle value on the antineutrino flux in a
supernova with a state-of-the-art numerical simulation, including the neutrinoneutrino
interaction and a dynamical density matter profile with shock-waves.
A characteristic signature of the hierarchy and the angle has been identified in
the positron signal associated to the inverse-beta process, in an observatory on
Earth. Finally, in the cosmological context, we have studied the impact of the
CP violating phase on the electron neutrino chemical potential shortly before primordial
nucleosynthesis. In addition to an analytical derivation which provides
the conditions for CP effects, we show the impact of the phase on the primordial
helium fraction.
Keywords: neutrinos, CP-violation, r-process, oscillation parameters, corecollapse
supernova, Big Bang nucleosynthesis, oscillation phenomenon.
191