Varying alpha, thresholds and fermion masses

We consider variations of coupling strengths and mass ratios in and beyond the Standard Model, in the light of various mechanisms of mass generation. In four-dimensional unified models, variations in charged particle thresholds, light quark masses and the electron mass can completely alter the (testable) relation between Delta In alpha and Delta In mu, where mu equivalent to m(p)/m(e), (C) 2003 Elsevier B.V. All rights reserved.