Nonspectator effects in B-> K^*+photon within the vector quark model

The tree level FCNC due to the presence of an additional generation of vector quarks result in the leading order nonspectator contributions to rare B-> K^*+photon decay mode. These tree level contributions are sensitive only to b-> s nonunitary parameter U^{sb} and therefore, provide a direct constraint on this model parameter. We obtain the isospin asymmetry between \bar B^0->\bar K^{*0}+photon and B^--> K^{*-}+photon to be \Delta_{0-}=-0.03*Re (U^{sb}/(a^c_7V_{tb}V^*_{ts})) and the direct CP asymmetry between B^+->K^{*+}+photon and B^--> K^{*-}+photon to be A_{CP}^{VQM}=0.27|U^{sb}/(V_{tb}V_{ts}^*)|*sin{\theta}*sin{\phi_s}, where \theta is the weak phase of U^{sb} and \phi_s is the strong phase of decay amplitude. We predict a direct CP asymmetry of around a few percent if the current experimental difference between \Delta_{0-} and \Delta_{0+} is to be explained by the presence of the additional vector quarks.