Direct CP asymmetry of B→Xd,sγ in a model with vector quarks

We investigate the effect of vector quarks on the inclusive decays B --> X(d,s)gamma. We show that the branching ratio of B --> X(d)gamma can differ sizably from the SM and MSSM predictions, being enhanced to present experimental observability or suppressed such that present runs of the B factories would not observe it. Current measurements of the direct CP asymmetry (A(CP)) for B --> X(s)gamma are sensitive to the contribution from B --> X(d)gamma. For a sufficiently enhanced BR(B --> X(d)gamma) we show that the dominant contribution to the combined asymmetry may be from B --> X(d)gamma. Thus any large value for A(CP) should not immediately be attributed to B --> X(s)gamma, which stresses the importance of good K/pi separation. (C) 2002 Elsevier Science B.V. All rights reserved.