Phenomenological Constraints on Extended Quark Sectors
We study the flavor physics in two extensions of the quark sector of the Standard Model (SM): a four generation model and a model with a single vector--like down--type quark (VDQ). In our analysis we take into account the experimental constraints from tree--level charged current processes, rare Kaon decay processes, rare B decay processes, the $Z\to b \bar{b}$ decay, $K$, $B$ and $D$ mass differences, and the CP violating parameters $\frac ε^\prime}ε$, $ε_K$ and $a_{ψK}$. All the constraints are taken at two sigma. We find bounds on parameters which can be used to represent the New Physics contributions in these models ($λ_{t^ \prime}^{bd}$, $λ_{t^ \prime}^{bs}$ and $λ_{t^ \prime}^{sd}$ in the four--generation model, and $U_{bd}$, $U_{bs}$ and $U_{sd}$ in the VDQ model) due to all the above constraints. In both models the predicted ranges for $a_{SL}$ (the CP asymmetry in semi-leptonic decays), $ΔM_D$, $B(K^+\toπ^+ ν\barν)$, $B(K_L\toπ^0 ν\barν)$ and $B(K_L\to μ\barμ)_{SD}$ can be significantly higher than the predictions of the SM, while the allowed ranges for $a_{ψK}$ and for $Δm_{B_S}$ are consistent with the SM prediction.