Twisted boundary conditions and matching to the effective four-dimensionaltheory

Nontrivial twisted boundary conditions associated with extra compact dimens ions can produce an ambiguity in the value of the four-dimensional coupling constants of the renormalizable interactions of the twisted fields' zero-m odes. Resolving this indeterminacy would require a knowledge of the exact f orm of the higher-dimensional action including the coefficients of higher-d imensional operators. For the case of moderately sized extra dimensions, th e uncertainty in the coupling constants can be of order one and may lead to modifications in the stability of the model.