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/sup 0/ CP asymmetries without conflicting with low-energy constraints. In the light of low CP asymmetry in B to J/ psi K/sub 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 to dll transition over the SM expectation. (25 refs).