SO(10) Grand Unification

The state of the art of SO(10) grand unification with or without supersymmetry is studied in detail. Various SO(10) models are reviewed, and new ones are constructed. In particular, the minimal supersymmetric (SUSY) SO(10) grand unified theory (GUT), which arises naturally as the best candidate for physics beyond the standard model of the electroweak and strong interactions that can accommodate non-zero neutrino mass and supersymmetry, is analyzed in detail. It is shown that the theory allows only single -step gauge symmetry breaking as the minimal SUSY SU(5) GUT but differently from minimal non-SUSY SO(10) models. It is also shown that detailed predictions for neutrino masses and mixings can be made in this theory, making it experimentally testable in the near future. Many interesting phenomenological implications such as degenerate neutrino masses, natural doublet-triplet splitting, natural suppression of colored -Higgsino mediated proton decay, invisible axion, hot dark matter neutrinos, etc., are explored within in the context of SO(10) grand unification. The new results presented in this dissertation show that SO(10) grand unification has more interesting possibilities than any other grand unification.