Sparticle Spectroscopy from SO(10) GUT with a Unified Higgs Sector

We study the low energy implications, especially the particle spectroscopy, of SO(10) grand unification in which the SO(10) symmetry is broken to the Standard Model gauge group with a single pair of (144+\bar144) dimensional Higgs multiplet (unified Higgs sector). In this class of models, the asymptotic relation Y_b \approx Y_\tau \approx Y_t/6 among the third generation quark and lepton Yukawa couplings can be derived. This relation leads to the prediction \tan\beta \approx 14, where \tan\beta is the well known MSSM parameter. We find that this type of Yukawa coupling unification (YU) is realized only by employing non-universal soft supersymmetry breaking terms, dictated by SO(10) symmetry, for the gauginos. A 125 GeV Higgs boson mass is also found to be consistent with YU at the \sim 5% level. Without imposing a constraint on the relic abundance of dark matter in these models, the squark and slepton masses, with the exception of the stop, exceed 2 TeV and the gluino is heavier than 1 TeV. We show that the neutralino in this model is an acceptable dark matter candidate through the neutralino-stop coannihilation scenario, with the stop quark being relatively light (\gtrsim 500 GeV).