Higgs Phenomenology as a Probe of Supersymmetric Grand Unification with the Hosotani Mechanism

In the supersymmetric SU(5) grand unified theory whose gauge symmetry is broken by virtue of the Hosotani mechanism, the huge mass splitting between the colored Higgs triplet and the electroweak Higgs doublet superfields is naturally realized. As a byproduct, the existence of adjoint chiral superfields with masses of the order of the supersymmetry breaking scale is predicted, leading to the Higgs sector that contains an SU(2)_L triplet chiral multiplet with hypercharge zero and a neutral singlet one in addition to the two SU(2)_L doublets of the minimal supersymmetric standard model. We focus on the Higgs sector and investigate to what extent the couplings of the standard model-like Higgs boson and the masses of the additional Higgs bosons deviate from those in the Standard Model and other models due to the new triplet and singlet chiral multiplets. We show that this model can be distinguished using precision measurements of couplings and masses of the Higgs sector particles and serves as a good example of grand unification testable at colliders such as the luminosity up-graded Large Hadron Collider and future electron-positron colliders.