An SO(10)XS-4 Scenario for Naturally Degenerate Neutrinos
  The simplest scenario for the three known light neutrinos that fits the solar and atmospheric neutrino deficit and a mixed dark matter (MDM) picture of the universe requires them to be highly degenerate with $m_{\nu} \sim$ 1 - 2 eV. We propose an SO(10) grand unified model with an S$_{4}$-horizontal symmetry that leads naturally to such a scenario.   An explicit numerical analysis of the quark and lepton sector of the model shows that it can lead to desired mass differences to fit all data only for the small angle non-adiabatic MSW solution to the solar neutrino puzzle. 
D. G. Lee and R. N. Mohapatra (University of Maryland)