Higher loop effects on unification via Kaluza–Klein thresholds Original Research Article

We discuss higher loop corrections to gauge coupling renormalization in the context of gauge coupling unification via Kaluza–Klein thresholds. We show that in the case of N=1 supersymmetric compactifications the one-loop threshold contributions are dominant, while the higher loop correction are subleading. This is due to the fact that at heavy Kaluza–Klein levels the spectrum as well as the interactions are N=2 supersymmetric. In particular, we give two different arguments leading to this result – one is field theoretic, while the second one utilizes the power of string perturbation techniques. To illustrate our discussions we perform explicit two-loop computations of various corrections to gauge couplings within this framework. We also remark on phenomenological applications of our discussions in the context of TeV-scale brane world.