An extended flipped SU(5) GUT model and the fermion mass hierarchy

We present a viable flipped version of the SU(5) model which may be embedded in SO(10) consistent with the phenomenological requirements of having a non-trivial quark mixing matrix, natural doublet-triplet splitting, and a single pair of light electroweak Higgs doublet scalar bosons. In the presence of suitable non-renormalizable superpotential terms the model can reproduce the hierarchy observed in quark masses and mixings as well as an acceptable neutrino mass generated via the seesaw mechanism needed to explain dark matter and solar neutrino data.