A five-dimensional SU(5) grand unified theory is constructed on the orbifold S/Z2, with gauge symmetry breaking accomplished by a background gauge field. The theory is shown to be equivalent to one with gauge symmetry breaking by orbifold boundary conditions — the two pictures are related by a non-periodic gauge transformation. This effective field theory possesses localized explicit breaking o...

In 1978 Gribov showed that the fixing of the divergence of the gauge field in non-Abelian gauge theory does not fix its gauge[1]. The restriction of the gauge field such that its Faddeev-Popov determinant is positive (Gribov region) is necessary yet insufficient for excluding the ambiguity. The restriction to the fundamental modular region[2,4] cancels the infrared singularity of the perturbati...