Exclusive $B \to V \gamma$ decays in the T2HDM

Abstract

By employing the QCD factorization approach for the exclusive $B \to V \gamma$ decays, we calculated the new physics contributions to the branching ratios, CP asymmetries, isospin and U-spin symmetry breaking of $B \to K^*\gamma$ and $B \to \rho \gamma$ decays, induced by the charged Higgs penguin diagrams appeared in the top-quark two-Higgs-doublet model(T2HDM). Within the considered parameter space, we found that (a) a charged-Higgs boson with a mass larger than 300 GeV are always allowed by the date of $B \to V \gamma$ decay, and such lower limit on $\mhp$ are comparable with those obtained from the inclusive $B \to X_s \gamma$ decay; (b) the CP asymmetry of $B \to \rho \gamma$ in the T2HDM can be as large as 10% in magnitude and has a strong dependence on the angle $\theta$ and the CKM angle $\gamma$; (c) the isospin symmetry breakings of $B \to V \gamma$ decays in the T2HDM are generally small in size: around 6% for $B \to K^* \gamma$ decay and less than 20% for $B \to \rho \gamma$ decay; and (d) the U-spin symmetry breaking $\Delta U(K^*,\rho)$ in the T2HDM is also small in size, only about 8% of the branching ratio $\calb (B \to \rho^0 \gamma)$.