Exclusive radiativeB-meson decays within minimal flavor-violating two-Higgs-doublet models

Abstract

In the ``Higgs basis'' for a generic two-Higgs-doublet model, only one doublet gets a nonzero vacuum expectation value and, under the criterion of minimal flavor violation, the other one is fixed to be either color-singlet or color-octet, referred to, respectively, as the type-III and type-C models. Both of them can naturally avoid large FCNC transitions and provide very interesting phenomena in some low-energy processes. In this paper, we study their effects on exclusive radiative $B$-meson decays due to the exchange of colorless or colored charged Higgs. It is found that while constraints from the branching ratios are slightly weaker than the ones from the inclusive $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ decay, the isospin asymmetries in exclusive decays provide very complementary bounds on the model parameters. As the two models predict similar corrections to the dipole coefficient ${C}_{7}^{\text{eff}}$, but similar magnitudes with opposite signs to ${C}_{8}^{\text{eff}}$, the branching ratios cannot discriminate the two models, and we have to resort to the direct $CP$ and isospin asymmetries of $b\ensuremath{\rightarrow}s$ processes, which are more sensitive to ${C}_{8}^{\text{eff}}$. Due to the CKM factors $|{\ensuremath{\lambda}}_{u}^{(d)}|\ensuremath{\sim}|{\ensuremath{\lambda}}_{t}^{(d)}|$, the terms proportional to ${\ensuremath{\lambda}}_{u}^{(d)}$ make the observables of $b\ensuremath{\rightarrow}d$ processes exhibit a different dependence on the possible new physics phase. In addition, correlations between the various observables in the exclusive $B\ensuremath{\rightarrow}V\ensuremath{\gamma}$ and the inclusive $B\ensuremath{\rightarrow}{X}_{s,d}\ensuremath{\gamma}$ decays are investigated, which could provide further insights into the models with more precise experimental measurements and theoretical predictions for these decays.