Bounds on Kaluza-Klein excitations of the SM vector bosons from electroweak tests

Within a minimal extension of the SM in 4 + 1 dimensions, we study how Kaluza-Klein excitations of the SM gauge bosons affect the electroweak precision observables. Asymmetries in Z decays provide the dominant bound on the compactification scale M of the extra dimension. If the higgs is so light that will be discovered at LEP2, we find the following 95% C.L. bounds: M > 3.5 TeV (if the higgs lives in the extra dimension) and M > 4.3 TeV (if the higgs is confined to our 4 dimensions). In the second case, Kaluza-Klein modes give 'universal' corrections and a good fit of precision data can be obtained with a heavier higgs (up to 500 GeV) and with a smaller M > 3.4 TeV. (C) 1999 Published by Elsevier Science B.V. All rights reserved