Light thresholds in Grand Unified Theories Original Research Article

In a generic Grand Unified Theory with a relatively small dispersion of the spectrum around the Z-boson and the unification masses, a connection is established, exact at one loop level, between MZ, GF, α(MZ and the strong coupling constant α3(MZ. At this level of precision, this avoids the logical and phenomenological inconsistency of predicting α3(MZ) by means of the electroweak couplings as extracted from the data in the Standard Model rather than in the complete theory. Attention is paid to the independence of the physical results from regularization and/or renormalization schemes.