Self-induced conversion in dense neutrino gases: Pendulum in flavour space

  title={Self-induced conversion in dense neutrino gases: Pendulum in flavour space},
  author={S.Hannestad and G.G.Raffelt and G.Sigl and Y.Y.Y.Wong},
Neutrino-neutrino interactions can lead to collective flavour conversion effects in supernovae and in the early universe. We demonstrate that the case of"bipolar"oscillations, where a dense gas of neutrinos and antineutrinos in equal numbers completely converts from one flavour to another even if the mixing angle is small, is equivalent to a pendulum in flavour space. Bipolar flavour conversion corresponds to the swinging of the pendulum, which begins in an unstable upright position (the… 
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