Regularisation Techniques for the Radiative Corrections of Wilson lines and

Within an effective field theory framework we compute the most general structure of the one-loop corrections to the 4D gauge couplings in one-and two-dimensional orbifold compacti-fications with non-vanishing constant gauge background (Wilson lines). Although such models are non-renormalisable, we keep the analysis general by considering the one-loop corrections in three regularisation schemes: dimensional regularisation (DR), Zeta-function regularisation (ZR) and proper-time cutoff regularisation (PT). The relations among the results obtained in these schemes are carefully addressed. With minimal re-definitions of the parameters involved, the results obtained for the radiative corrections can be applied to most orbifold compactifica-tions with one or two compact dimensions. The link with string theory is discussed. We mention a possible implication for the gauge couplings unification in such models.