Isospin Symmetry Breaking in B->K^* \gamma Decay due to an Extra   Generation of Vector Quarks
  The extra contributions due to an extra generation of vector-like quarks to the isospin symmetry breaking observable associated with the radiative B->K^* \gamma decay is obtained. It is shown that this additional contribution is sensitive to the nonunitarity parameter U^{sb}, which is a measure of the the strength of the non-zero tree-level flavor changing neutral current in this model. The significance of this result is that, once accurate experimental resultson the isospin asymmetry becomes available, one can constrain the U^{sb} independent of the mass of the extra quarks and so a much more stringent acceptablemodel parameter space could be obtained. 
Mohammad R. Ahmady and Farrukh Chishtie