Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
Figure 5.4: Total νe survival probability as a function of time, where τ ≡
(∆m 2 /2p0)t and p0 ≃ 2.2 T. The curves are for different values κ of the neutrino
self-coupling as indicated where κ = 0 corresponds to vacuum oscillations.
Figure 5.5: Evolution of the νe survival probability for three values of the neutrino
momenta in the presence of a strong neutrino self-potential term (κ = 10).
Fig.(5.4). But when κ is fixed to a high value, which means the self-interactions
are important, then even from three different values of momentum, the oscillations
are pretty much synchronized as one can see on Fig.(5.5) This behaviour
can happen in the Early Universe or in core-collapse supernova. In the latter
environment there is matter and the density of neutrinos is decreasing with time.
This implies the possible presence of a bipolar regime.
5.2.2 The bipolar regime
Neutrino-neutrino interaction can lead to collective flavor conversion effects in
supernovae when bipolar oscillations occur, even when the mixing angle is very
small, contrary to the usual MSW effect. Such behaviour can be interpreted as a
pendulum in flavour space, using the polarization vector formalism. We first show
the possibility to describe the system as an oscillating pendulum in the simplest
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