Atmospheric neutrino oscillations and maximal νμ−ντ mixing in unified models

The recent data describing the evidence for neutrino oscillations by Super Kamiokande implies that two neutrinos are very strongly mixed. We ask the question: can approximate maximal neutrino mixing be natural in unified (GUT or string) models? We attempt to answer this question in as much generality as possible. Without specifying a particular model, we are able to show that a gauged family symmetry can naturally provide the required maximal mixing between μ and τ neutrinos. The second and third family neutrino mass eigenstates are almost degenerate with masses of order 0.2 eV.