New doublet-triplet splitting mechanism for supersymmetric SO(10) and implications for fermion masses

We present a now mechanism for doublet-triplet splitting in supersymmetric SO(10) models using a missing vacuum expectation value pattern which is different from the one used in the currently popular Dimopoulos-Wilczek method. In our method, the doublets in a 16, <(16)over bar> pair are the ones split from the rest of the multiplet and are then mixed with the doublets from one or two 10's, giving rise to the doublets H-u and H-d of the standard model. This approach provides a natural way to understand why top quark is so much heavier than the bottom quark. It also enables us to generate both hierarchical and nonhierarchical patterns for neutrino masses, the latter being of interest if neutrino is the hot component of the dark matter of the universe. [S0031-9007(99)08871-7].