Study on the rare radiative decay Bc-->Ds* gamma in the standard model and multiscale walking technicolor model.

Abstract

Applying the perturbative QCD method, we study the decay {ital B}{sub {ital c}}{r_arrow}{ital D}{sub {ital s}}{sup {asterisk}}{gamma} in the standard model (SM) and multiscale walking technicolor model (MWTCM). In the SM, we find that the contribution of weak annihilation is more important than that of the electromagnetic penguin diagram. The presence of pseudo Goldstone bosons in the MWTCM leads to a large enhancement in the rate of {ital B}{sub {ital c}}{r_arrow}{ital D}{sub {ital s}}{sup {asterisk}}{gamma}, but this model is in conflict with the branching ratio of {ital Z}{r_arrow}{ital b{bar b}}({ital R}{sub {ital b}}) and the CLEO data on the branching ratio {ital B}({ital b}{r_arrow}{ital s}{gamma}). If top-color is further introduced, the calculated results in the top-color-assisted MWTCM can be suppressed and be in agreement with the CLEO data for a certain range of parameters. {copyright}{ital 1996 The American Physical Society.}