We study, at the one loop level, the dominant new physics contributions from extra dimensions to $\overrightarrow{Z}b\overline{b},$ as well as $B-\overline{B}$ and $K-\overline{K}$ mixing. We use a model with one extra dimension containing fermions which live in four dimensions, and gauge bosons and one scalar doublet propagating in five dimensions. We find that the effect of the infinite tower of Kaluza-Klein modes in $\overrightarrow{Z}b\overline{b}$ is finite and gives a negative correction to $R_b={\Gamma }_b/{\Gamma }_h,$ which is used to set a lower bound of 1 TeV on the compactification scale $M_c.$ On the other hand, we show that the box diagrams contributing to $B-\overline{B}$ and $K-\overline{K}$ mixing are divergent and, after proper regularization, we find that they increase the value of the function ${S(x}_t)$ which governs this mixing. The obtained value is perfectly compatible with available data.

• Received 15 August 2000

DOI:https://doi.org/10.1103/PhysRevD.63.016002