We suggest that recent puzzles in neutrino physics, i.e., the solar and atmospheric neutrino deficits, possible neutrino oscillations reported by the LSND, and neutrinos as hot dark matter, can all be naturally explained by assuming the existence of a mirror world described by an ‘‘electroweak’’ gauge symmetry [SU(2)×U(1)]′, with the breaking scale larger by about a factor of 30 than the scale of the standard SU(2)×U(1) model. Such models are motivated by the superstring ${\mathrm{E}}_8$×${\mathrm{E}}_8^{\prime }$ theories. The model also suggests that the bulk of the dark matter in the universe may be warm dark matter consisting of keV mirror particles rather than the conventional cold dark matter.

• Received 1 June 1995

DOI:https://doi.org/10.1103/PhysRevD.52.6607