Grand gauge-Higgs unification

We propose a novel way to break grand unified gauge symmetries via the Hosotani mechanism in models that can accommodate chiral fermions. Adjoint scalar fields are realized through the so-called diagonal embedding method which is often used in the heterotic string theory. We calculate the one-loop effective potential of the adjoint scalar field in a five dimensional model compactified on an S1/Z₂ orbifold, as an illustration. It turns out that the potential is basically the same as the one in an S1 model, and thus the results in literatures, in addition to the chiral fermions, can be realized easily.