Theoretical uncertainties and phenomenological aspects of B →Xs γ decay

We analyze uncertainties in the theoretical prediction for the inclusive branching ratio BR[B →Xs γ]. We find that the dominant uncertainty in the leading order expression comes from its μ-dependence. We discuss a next-to-leading order calculation of B →Xs γ in general terms and check to what extent the μ-dependence can be reduced in such a calculation. We present constraints on the Standard and Two-Higgs-Doublet Model parameters coming from the measurement of b →s γ decay. The current theoretical uncertainties do not allow one to definitively restrict the Standard Model parameters much beyond the limits coming from other experiments. The bounds on the Two-Higgs-Doublet Model remain very strong, though significantly weaker than the ones present in the recent literature. In the Two-Higgs-Doublet Model case, the b →s γ, Z →b b and b →c τ anti ντ processes are enough to give the most restrictive bounds in the MH±-tan β plane. ((orig.))