Tree-level flavor-changing neutral currents in the B system: From CP asymmetries 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-o CP asymmetries without conflicting with low-energy constraints. In the light of low CP asymmetry in B-->J/psi 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 O(20) enhancement of the b-->dl (l) over bar transition over the SM expectation