Exclusive $B\to (K^{\ast },\rho )\gamma$ decays in the general two-Higgs-doublet models

Abstract

By employing the QCD factorization approach, we calculated the next-to-leading order new physics contributions to the branching ratios, CP asymmetries, isospin and U-spin symmetry breaking of the exclusive decays $B\to V\gamma$ ($V=K^{\ast },\rho$), induced by the charged Higgs penguins in the general two-Higgs-doublet models. Within the considered parameter space, we found that (a) the new physics corrections to the observables are generally small in the model I and model III-A, moderate in model II, but large in model III-B; (b) from the well measured branching ratios and upper limits, a lower bound of $\mhp > 200$ GeV in model II was obtained, while the allowed range of $\mhp$ in model III-B is $ 226 \leq \mhp \leq 293 $ GeV; these bounds are comparable with those from the inclusive $B\to X_s\gamma$ decay; (c)the NLO Wilson coefficient $C_7(m_b)$ in model III-B is positive and disfavered by the measured value of isospin symmetry breaking ${\Delta }_{0-}^{exp}(K^{\ast }\gamma )=(3.9\pm 4.8)$, but still can not be excluded if we take the large errors into account; (d) the CP asymmetry $\acp(B \to ργ)$ in model III-B has an opposite sign with the one in the standard model (SM), which may be used as a good observable to distinguish the SM from model III-B; (e) the isospin symmetry breaking $\Delta (\rho \gamma )$ is less than 10% in the region of $\gamma =[40\sim 70{]}^{\circ }$ preferred by the global fit result, but can be as large as 20 to 40% in the regions of $\gamma \le 10^{\circ }$ and $\gamma \ge 120^{\circ }$. The SM and model III-B predictions for $\Delta (\rho \gamma )$ are opposite in sign for small or large values of the CKM angles; (f) the U-spin symmetry breaking $\Delta U(K^{\ast },\rho )$ in the SM and the general two-Higgs-doublet models is generally small in size: $\sim 10^{-7}$.

Revtex, 38 pages with 14 eps figures, minor corrections