  Supersymmetric grand unified theories based on the gauge group SO(10) are
highly motivated. In the simplest models, one expects t-b-\tau Yukawa coupling
unification, in addition to gauge, matter and Higgs unification. Yukawa
unification only occurs with very special GUT scale boundary conditions,
leading to a spectra with ~10 TeV first and second generation scalars,
TeV-scale third generation scalars, and light gauginos. The relic density of
neutralino cold dark matter is calculated to be 10^2-10^4 times higher than
observation. If we extend the theory with the PQWW solution to the strong CP
problem, then instead a mixture of axions and axinos comprises the dark matter,
with the measured abundance. Such a solution solves several cosmological
problems. We predict a rather light gluino with m(gluino)~300-500 GeV that
should be visible in either Tevatron or forthcoming LHC run 1 data. We would
also expect ultimately a positive result from relic axion search experiments.
