Next-to-Leading QCD Corrections to B \to X_{s}\gamma: Standard Model and Two-Higgs Doublet Model

We present the QCD corrections to the matching conditions of the Delta B =1 magnetic and chromo-magnetic operators in the Standard Model and in two-Higgs doublet models. We use an off-shell matching procedure which allows us to perform the computation using Taylor series in the external momenta, instead of asymptotic expansions. In the Standard Model case, we confirm previous results derived on-shell and we obtain BR(B -> X_s gamma)=(3.51\pm 0.31) 10^{-4}. In the case of the usual two-Higgs doublet model, we show that going from the leading to the next-to-leading order result drastically improves the CLEO bound on the charged-Higgs mass from 280 GeV to 460 GeV. This limit is very sensitive to the definition of errors and we carefully discuss the theoretical uncertainties. Finally, in the case of the two-Higgs doublet model in which both up- and down-type quarks couple to the same Higgs field, the theoretical prediction for BR(B -> X_s gamma) can be reduced by at most 20% with respect to the Standard Model value.