Time variation of coupling constants in Kaluza-Klein cosmologies

We present a cosmological analysis of a six-dimensional Einstein-Yang-Mills-Higgs model with SO(3) invariance to which is added a matter term. An analytical expression for the time variation of the internal radius is obtained together with the predictions for the variations of the coupling ‘‘constants’’ involved. Their variation is limited to the very early stages of the cosmological evolution since the internal radius quickly becomes constant. It is shown that, once the asymptotic behavior sets in, the four-dimensional space-time expands linearly in time with a zero effective cosmological constant, after fine tuning.