We study the nature of the seesaw mechanism in the context of renormalizable SO(10) with Higgs fields in the 10-plets and $\overline{126}$-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 seesaw.

• Received 29 April 2004

DOI:https://doi.org/10.1103/PhysRevD.70.093002