2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/52283We discuss the gauge coupling renormalization in orbifold field theories in which the 4-dimensional graviton and/or matter fields are quasi-localized in extra dimension to generate hierarchically different mass scales and/or Yukawa couplings. In such theories, there can be large calculable Kaluza-Klein threshold corrections to low energy gauge couplings, enhanced by the logarithms of small warp factor and/or of small Yukawa couplings. We present the results on those Kaluza-Klein threshold corrections in generic 5-dimensional theory on $S^1/Z_2\times Z_2$ containing arbitrary 5-dimensional gauge, spinor and scalar fields.Some minor typos are corrected. 10 pages, Revtex4, Talk presented at Summer Institute 2003, Fuji-Yoshida, Japan (Aug. 12-19, 2003). To appear in the ProceedingsHigh Energy Physics - TheoryHigh Energy Physics - Phenomenologytext