Tree-level flavor-changing neutral currents in theBsystem: FromCPasymmetries to rare decays

Tree-level flavor-changing neutral currents (FCNC) are characteristic of models with extra vectorlike quarks. These new couplings can strongly modify the $B^0\hspace{0.5em}\mathrm{CP}$ asymmetries without conflicting with low-energy constraints. In the light of low $\mathrm{CP}$ asymmetry in $\overrightarrow{B}J/\psi \hspace{0.5em}{K}_S,$ we discuss the implications of these contributions. We find that even these low values can be easily accommodated in these models. Furthermore, we show that the new data from B factories tend to favor an $\mathcal{O}\mathrm{}\left(20\right)\mathrm{}$ enhancement of the $\overrightarrow{b}\mathrm{dl}\overline{l}$ transition over the SM expectation.