  The supersymmetric grand unified theory where the SU(5) gauge symmetry is
broken by the Hosotani mechanism predicts the existence of adjoint chiral
superfields whose masses are at the supersymmetry breaking scale. The Higgs
sector is extended with the SU(2)_L triplet with hypercharge zero and neutral
singlet chiral multiplets from that in the minimal supersymmetric standard
model. Since the triplet and singlet chiral multiplets originate from a
higher-dimensional vector multiplet, this model is highly predictive.
Properties of the particles in the Higgs sector are characteristic and can be
different from those in the Standard Model and other models. We evaluate
deviations in coupling constants of the standard model-like Higgs boson and the
mass spectrum of the additional Higgs bosons. We find that our model is
discriminative from the others by precision measurements of these coupling
constants and masses of the additional Higgs bosons. This model can be a good
example of grand unification that is testable at future collider experiments
such as the luminosity up-graded Large Hadron Collider and future
electron-positron colliders.
