Bi-Maximal Neutrino Mixing in SO(10)_{GUT}
  We find a grand unified SO(10) model which accommodates the bi-maximal neutrino mixing for vacuum-oscillation solutions to the atmospheric and the solar neutrino problems. This model maintains the original SO(10) mass relation between neutrino and up-type quark masses, $m_{\nu_2} / m_{\nu_3} \sim (m_{c}/m_{t})^2$. 
Yasunori Nomura and T. Yanagida