DirectCPviolation in radiativebdecays in and beyond the standard model

We consider the partial rate asymmetry in the inclusive decay modes $\overrightarrow{b}s\gamma$ and $\overrightarrow{b}d\gamma ,$ concentrating on non-standard models with new charged Higgs interactions. We find that the charged Higgs contribution to the asymmetry for $\overrightarrow{b}s\gamma$ is small in such models due to a universal cancellation mechanism. The asymmetry is therefore difficult to distinguish experimentally from the standard model (SM) value, which is also small. The cancellation mechanism is found to be rendered inoperative in supersymmetry due to the presence of chargino loops. Unlike $\overrightarrow{b}s\gamma ,$ the rate asymmetry for $\overrightarrow{b}d\gamma$ in Higgs models can be quite different from its SM value, generally ranging from $-20\%$ to $+20\%.\mathrm{}$ Specific model calculations are performed for the three-Higgs-doublet model and the “top” two-Higgs-doublet model to serve as illustrations. We also offer some suggestions that may be helpful to experimentalists in the detection of the inclusive mode $\overrightarrow{b}d\gamma .$