Getting bounds on the mixing angles for a non-sequential bottom quark

We analyze the vertex Zff in the framework of models that add a new bottom quark in a nonsequential way and we evaluate the tree level contribution to LEP/SLC data $R_{b}$, $R_{l}$ and the total Z width $\Gamma_{Z}$. We obtain bounds for the mixing angles through the experimentally allowed contour regions of the parameters $\Lambda_{L,R}$ introduced here. In order to get a more restrictive region, we also consider the experimental results for $B\to \nu \nu X$ as well.