LEP Constraints on 5-Dimensional Extensions of the Standard Model

We study minimal 5-dimensional extensions of the Standard Model, in which all or only some of the SU(2)${}_L$ and U(1)${}_Y$ gauge fields and Higgs bosons propagate in the fifth compact dimension. In all the 5-dimensional settings, the fermions are assumed to be localized on a 3-brane. In addition, we present the consistent procedure for quantizing 5-dimensional models in the generalized $R_{\xi }$ gauge. Bounds on the compactification scale between 4 and 6 TeV, depending on the model, are established by analyzing electroweak precision measurements and LEP2 cross sections.