Varying alpha, thresholds and extra dimensions

Thomas Dent

Published 2003-05-02, updated 2003-08-26Version 2

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, heavy quark and superparticle thresholds and the electron mass can completely alter the (testable) relation between Delta ln alpha and Delta ln mu, where mu \equiv m_p/m_e. In extra-dimensional models where a compactification scale below the fundamental scale is varying, definite predictions may result even without unification; we examine some models with Scherk-Schwarz supersymmetry-breaking.