Origin of neutrino masses and mixings
  A brief overview of the important theoretical issues in neutrino physics is presented and some of the current ideas for addressing them in the framework of the seesaw mechanism of neutrino masses are discussed. Among the topics discussed are ways to understand maximal mixing pattern among the three neutrino species, both uni-maximal and bimaximal kinds. Constraints from baryogenesis on mixing patterns are noted. In the last section, the question of understanding the small masses for sterile neutrinos, which seem to be needed for various reasons is addressed. 
R. N. Mohapatra