Universality limits on bulk fermions

The Kaluza–Klein fermion excitations induce mixing between the Standard Model 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 these masses go to infinity. This implies a bound on the lightest new heavy quark, M1≳3–5 TeV, which together with the electroweak precision data limits will allow the large hadron collider to provide a crucial test of the Randall–Sundrum ansatz for solving the gauge hierarchy.