Universal extra dimensions andZ→bb¯

We study, at the one loop level, the dominant contributions from a single universal extra dimension to the process $\overrightarrow{Z}b\overline{b}.$ By resorting to the gaugeless limit of the theory we explain why the result is expected to display a strong dependence on the mass of the top quark, not identified in the early literature. A detailed calculation corroborates this expectation, giving rise to a lower bound for the compactification scale which is comparable to that obtained from the $\rho$ parameter. An estimate of the subleading corrections is furnished, together with a qualitative discussion on the difference between the present results and those derived previously for the nonuniversal case.