Universality limits on bulk fermions

The Kaluza-Klein fermion excitations induce mixing between the Standard Mod el fermions and loss of universality. The flavour mixing not present in the Standard Model can be made to vanish aligning the Yukawa couplings and the Dirac masses of the heavy modes, but universality is only recovered when t hese masses go to infinity. This implies a bound on the lightest new heavy quark, M-1 greater than or similar to 3-5 TeV, which together with the elec troweak precision data limits will allow the large hadron collider to provi de a crucial test of the Randall-Sundrum ansatz for solving the gauge hiera rchy. (C) 2000 Published by Elsevier Science B.V.