Grand Unification and Time Variation of the Gauge Couplings

Astrophysical indications that the fine structure constant is time dependent are discussed in the framework of grand unification models. A variation of the electromagnetic coupling constant could either be generated by a corresponding time variation of the unified coupling constant or by a time variation of the unification scale, or by both. The case in which the time variation of the electromagnetic coupling constant is caused by a time variation of the unification scale is of special interest. It is supported in addition by recent hints towards a time change of the proton-electron mass ratio. Possible implications for baryogenesis are discussed. The study of a possible time variation of the fundamental parameters like for example the fine structure constant, has a long history that can be traced back to Dirac [1]. Some extensions of the standard model of particle physics and in particular models that couple gravity to the standard model, e.g. quintessence [2], require or at least allow a time dependence of the parameters of the model. Our motivation to study the implications of a time dependence of the fundamental parameters for particle physics is not that much of a theoretical origin but rather because there are indications [3, 4, 5, 6, 7, 8] coming from different astrophysical measurements that the parameters of the standard model could be time dependent. We shall consider the implications of Webb et al.’s result which indicate a possible time dependence of "