XXth International Conference on Neutrino Physics and Astrophysics
S.Pastor (MPI Physik, Munich, Germany)
Neutrino oscillations in dense neutrino media
In the early universe or in some regions of supernovae, the neutrino
refractive index is dominated by the neutrinos themselves. Several
previous studies have found numerically that these self-interactions
have the effect of coupling different neutrino modes in such a way as
to synchronize the flavor oscillations which otherwise would depend on
the energy of a given mode. We show a simple explanation for this
baffling phenomenon in analogy to a system of magnetic dipoles which
are coupled by their self-interactions to form one large magnetic
dipole which then precesses coherently in a weak external magnetic
field. As an application, we study three-flavor neutrino oscillations
in the early universe in the presence of neutrino chemical
potential. We found that effective flavor equilibrium between all
active neutrino species is established well before the big-bang
nucleosynthesis epoch if the neutrino oscillation parameters are in
the range indicated by the atmospheric neutrino data and by the large
mixing angle MSW solution of the solar neutrino problem.
Based on Phys. Rev. D 65 (2002) 053011 and
hep-ph/0201287