Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
are massive particles, and therefore oscillate which means that while traveling
they can change their flavour.
Super-Kamiokande first brought the crucial discovery of neutrino oscillation
in 1998 by measuring a νµ deficit for up-going atmospheric neutrinos compared to
down going ones in the detector. This was the first experimental proof of physics
beyond the Standard Model. In 2000, the experimental results of SNO were the
first to clearly indicate that the total flux of neutrinos detected by neutral current
interactions was compatible with the standard solar models. Finding a smaller νe
flux than expected meant that some of them have oscillated into another flavour.
Wolfenstein in 1978, then Mikheyev and Smirnov in 1986 proposed a mechanism
for neutrinos to undergo a resonant flavour conversion in their oscillation
while propagating through matter (which became to be known as the MSW effect).
It was Bethe who showed that an adiabatic conversion might occur in the
Sun and be at the origin of the solar neutrino deficit. In 2002 Kamland identified
the large mixing angle solution to the solar neutrino deficit problem giving the
first experimental evidence that the MSW effect occurs in the Sun.
The discovery of neutrino oscillation has an enormous impact in various domains
of physics. In particular it implies that the neutrino interaction and mass
basis are not identical and are related by a mixing matrix. This matrix was
proposed in 1962 by Maki, Nakagawa, and Sakata who supposed 3 flavour family
of neutrinos. This matrix may be complex and in addition to three mixing angles,
it possesses a complex term containing the CP-violating phase. Important
questions remain open, such as the neutrino nature (Majorana versus Dirac),
the value of θ13, the hierarchy problem, and the possible existence of CP violation
in the lepton sector. In particular the CP-violation can help explaining the
matter-antimatter asymmetry in the Universe, one of the fundamental questions
in cosmology.
In 1987, Kamiokande, IMB and Baksan detected for the first time neutrinos
coming from a supernova explosion near our galaxy. The observation of solar
and 1987A neutrinos opened the era of neutrino astronomy. This event, proving
that core-collapse supernovae are producing neutrinos, has already furnished
constraints about particle physics, and given information on neutrinos and on
the supernova explosion mechanism. Several problems still remain concerning
supernovae. We do not have a perfectly clear picture of the explosion mechanism,
and the precise astrophysical conditions under which the heavy elements
are produced still remain unknown.
The aim of this thesis is to investigate the neutrino properties using astrophysical
and cosmological contexts. CP-violation in the lepton sector is a crucial
issue which depending on the value of the third mixing angle, might require very
long term accelerator facilities. We explore for the first time the possibility to use
supernova neutrinos to learn about the Dirac phase either from direct effects in
a observatory or from indirect effects in the star. We first study the influence of
the CP-violating phase in the neutrino propagation inside the supernova within
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