  This work presents a complete analysis of fermion fitting and proton decay in
a SUSY $SO(10)$ model previously suggested by Dutta, Mimura, and Mohapatra.
  A key question in any grand unified theory is whether it satisfies the
experimental lower limits on proton partial lifetimes. In generic models,
substantial fine-tuning is required among GUT-scale parameters to satisfy the
limits. In the proposed model, the ${\bf 10}$, $\overline{\bf{126}}$, and ${\bf
120}$ Yukawa couplings contributing to fermion masses have restricted textures
intended to give favorable results for proton lifetime, while still giving rise
to a realistic fermion sector, without the need for fine-tuning, even for large
$\tan\beta$, and for either type-I or type-II dominance in the neutrino mass
matrix.
  In this thesis, I investigate the above hypothesis at a strict numerical
level of scrutiny; I obtain a valid fit for the entire fermion sector for both
types of seesaw dominance, including $\theta_{13}$ in good agreement with the
most recent data. For the case with type-II seesaw, I find that, using the
Yukawa couplings fixed by the successful fermion sector fit, proton partial
lifetime limits are readily satisfied for all but one of the pertinent decay
modes for nearly arbitrary values of the triplet-Higgs mixing parameters, with
the $K^+ \bar\nu$ mode requiring a ${\cal O}(10^{-1})$ cancellation in order to
satisfy its limit. I also find a maximum partial lifetime for that mode of
$\tau(K^+ \bar\nu) \sim 10^{36}\,$years. For the type-I seesaw case, I find
that $K^+ \bar\nu$ decay mode is satisfied for any values of the triplet mixing
parameters giving no major enhancement, and all other modes are easily
satisfied for arbitrary mixing values; I also find a maximum partial lifetime
for $K^+ \bar\nu$ of nearly $10^{38}\,$years, which is sub-dominant to gauge
boson decay channels.

High Energy Physics - Phenomenology