Bimaximal mixing from lopsided neutrinos
  We consider the problem of neutrino masses and mixing within the general framework of standard (type-I) seesaw models leading to three light neutrinos. Under the assumption of a hierarchical neutrino mass spectrum \lambda^4: \lambda : 1, consistent with present data, we examine possible lopsided patterns for the neutrino Yukawa couplings that can account for the observed mixing angles, including a small but non-vanishing |U_{e3}|. An embedding of the above within a general class of SO(10) models is also considered. 
M. Paraskevas and K. Tamvakis
hep-ph