Orbifold unification for the gauge and Higgs fields and their couplings

We present an orbifold GUT model in which the Higgs trilinear couplings are unified with the three Standard Model gauge couplings. The model is constructed as an N=2 supersymmetric SU(8) gauge theory in six dimensions, which is reduced to a supersymmetric Standard Model with three singlets and extra U(1) factors upon compactification. Such an unification is in good agreement with experiments. The predicted upper limit for the lightest CP-even neutral Higgs boson is somewhat larger than in the MSSM, and can be tested in the upcoming large hadron collider.