Vector Quark Model and $B$ Meson Radiative Decay

We study the $B$ meson radiative decay $B \to X_s \gamma$ in the vector quark model. Deviation from the Standard Model arises from the non-unitarity of the charged current KM matrix and related new FCNC interactions. We establish the relation between the non-unitarity of charged current mixing matrix and the mixing among the vector quark and the ordinary quarks. We also make explicitly the close connection between this non-unitarity and the flavor changing neutral currents. The complete calculation including leading logarithmic QCD correction is carefully carried out. Using the most updated data and the NLO theoretical calculation, the branching fraction of the observed $B$ meson radiative decay places a limit on the mixing angles as stringent as that from the process $B\to X \mu\bar\mu$.