Textures for Atmospheric and Solar Neutrino Oscillations
  In theories with three light neutrinos, a complete list of five zeroth-order textures for lepton mass matrices is found, which naturally yield: m_e = m_mu=0, m_tau \neq 0, Delta m^2_sun = 0, together with theta_{e tau} = 0, theta_{mu tau} approx 1. These textures provide suitable starting points for constructing theories which account for both atmospheric and solar neutrino fluxes. Using flavor symmetries, two schemes for such lepton masses are found, and example constructions exhibited. 
Riccardo Barbieri, Lawrence J. Hall and Alessandro Strumia