MSGUT : the next Avtar
  We report the viability of the Type I seesaw mechanism in 3 generation renormalizable SO(10) GUTs based on the $\mathbf{{210-10-\oot-126-120}}$ Higgs system. The $\mathbf{120}$ -plet and $ \mathbf{10}$-plet Higgs fit charged fermion masses while small $\mathbf{\bar{126}} $-plet couplings enhance Type I seesaw neutrino masses to viable values and make the fit to light fermions accurate. For the 3 generation CP conserving case we display accurate charged fermion fits ($\chi^2_{tot} < .2 $) which imply Type I neutrino masses $10^2- 10^3$ times larger than the $\mathbf{10-\bar{126}}$ scenario. The correct ratio of neutrino mass squared splitting, large($\theta_{23}^{PMNS}$) and small($\theta_{13}^{PMNS}$) mixing angle are achievable. $\theta_{12}^{PMNS}$ is however small and indicates that -as in the Type I $\mathbf{10-\oot}$ case - a fully realistic fit to the lepton mixing data also \emph{requires} CP violation. 
Charanjit S.Aulakh