Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
In this thesis, we have studied several unknown neutrino properties in the
astrophysical and also cosmological contexts.
The two first works have focussed on the study of possible effects coming from
the CP-violating Dirac phase δ in the supernova environment. Many questions
remain concerning supernova physics such as the the precise mechanism of the
explosion and the nucleosynthesis of heavy elements (r-process). Neutrinos may
bring some answers, since electron (anti-) neutrinos interact with matter and influence
the supernova observables like the electron fraction. Therefore, besides
getting information on this crucial open question, the study of the influence of
the unknown CP-violating phase on the neutrino fluxes and on the electron fraction
could bring a new understanding of these open issues. Investigating such a
possibility, we have first derived an analytic formula proving that no CP-violating
effects could be present in the electron (anti-) neutrino flux and a fortiori in the
electron fraction, if and only if the flux of νµ is equal to the flux of ντ at the neutrinosphere.
Our demonstration is exact and valid for any matter density profile.
This result validates all the litterature that uses the latter hypothesis while not
considering the leptonic CP-violating phase. By relaxing this assumption, thanks
to a code that we have developped, we have obtained that small effects can come
–from a non-zero δ– on the νe (¯νe) flux and on the electron fraction. We have
also numerically calculated the effects of this Dirac phase on the number of events
produced by electron anti-neutrinos via inverse beta reactions in an observatory
on Earth.
Actually, the first picture of neutrino interacting with matter inside the supernova
that we have based our calculation upon, was incomplete. First, one
has to take into account the one-loop corrections with matter. We have showed
that such a term differentiates νµ from ντ and induces a δ dependence on the
electron (anti-) neutrino survival probability, and consequently on the electron
(anti-) neutrino flux.
In addition to such a correction, a new paradigm in neutrino physics has
settled during the last few years: neutrino-neutrino interactions must be taken
into account. Using a different approach, to analytically study the influence of
the ν − ν interaction when δ is non zero, we have demonstrated that only when
taking different νµ and ντ fluxes, a δ dependence can arise from this term, in a
similar way as when one-loop corrections are considered. On the other hand, a
new phenomenology is associated to such non-linear interactions that we have
included in our previous code. Reproducing the different collective behaviours
that emerge, we have studied the consequences of this new interaction on the νe
and ¯νe fluxes inside the supernova, taking a non zero δ. It turns out that the
non-linearity amplifies the effects of δ present, due to the one-loop corrections,
to a possible 10% effect in the supernova.
In the same time than the development of numerically demanding neutrinoneutrino
interaction codes, people have also been interested in an important enhancement
of supernova models used in neutrino astrophysics, the use of a dy-
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