Rare decays B → Xsγ and Xsl+l- in vectorlike quark model

In the framework of vectorlike quark model (VQM), we present a comprehensive analysis for rare decays B → Xsγ and B → Xsl+l- including (1) the QCD running from the mass of the down-type vector quark D to weak scale in the scenario with the D quark much heavier than weak scale, (2) the extraction of the bounds on the interaction coupling of Zs-bar b, zsb from the experimental measurements for B → Xsl+l-, (3) various observables such as forward-backward (FB) asymmetry of b → sl+l-, the decay rate of B → Xsγ. We found that the constraints on the size of zsb and its CP phase are rather stringent, and |zsb| < 1.24 x 10-3. Subject to the bounds, the zero point s0 of the FB asymmetry still has large derivation form that of the SM and is very sensitive to zsb, and thus can be useful in probing new physics. (author)