  The effects of collective neutrino-plasma interactions on the linear wave
spectrum supported by a magnetized electron-positron plasma in the presence of
a neutrino-antineutrino medium are investigated. When a pair-symmetric
background neutrino-plasma medium is perturbed by space-charge waves
(electrostatic waves associated with electron-positron charge separation), our
analysis shows that the neutrino and antineutrino fluids also separate and the
pair symmetry of the background medium is broken. The cosmological implications
of this pair-symmetry breaking mechanism are briefly discussed.
