Probing the nature of the seesaw in renormalizable SO(10)
  We study the nature of the see-saw mechanism in the context of renormalizable SO(10) with Higgs fields in the 10-plets and 126-plet representations, paying special attention to the supersymmetric case. We discuss analytically the situation for the second and third generations of fermions ignoring any CP violating phase. It is shown that b-tau unification and large atmospheric mixing angle strongly disfavor the dominance of the type I see-saw. 
Borut Bajc, Goran Senjanovic and Francesco Vissani