Electroweak symmetry breaking and radion stabilization in universal extra dimensions

We discuss the stabilization of the scalar sector, including the radion, inthe gauge model with one universal extra dimension, within Higgs and Higgslessscenarios. The stabilization occurs at the one-loop level, through thefermionic contribution to the effective potential; in the Higgs case, forstabilization to take place the bosonic contribution must be balanced by thefermionic one, hence the scales of these two cannot differ too much. However,there is no need for (softly broken) supersymmetry to achieve the stabilization- it can be arranged for a reasonably wide range of couplings and mass scales.The primary instability in the model is the run-away of the radion vacuumexpectation value. It turns out that the requirement of the radion stability,in the Higgs case, favours a Higgs boson mass below 0.26 TeV, which isconsistent with the Standard Model upper bound that follows from theelectroweak precision measurements. The typical radion mass is of the order of10^{-6} eV. The radion mass can be made larger by rising the scale of fermionmasses, as clearly seen in the Higgsless case. The cosmological constant may becancelled by suitable counterterms, in such a way that the stabilization is notaffected.Comment: 20 pages, 2 figures, references adde