THEORETICAL UNCERTAINTIES AND PHENOMENOLOGICAL ASPECTS OF B-]X(S)GAMMA DECAY

We analyze uncertainties in the theoretical prediction for the inclusi ve branching ratio BR [B --> X(s) gamma]. We find that the dominant un certainty in the leading order expression comes from its mu-dependence . We discuss a next-to-leading order calculation of B --> X(s) gamma i n general terms and check to what extent the mu-dependence can be redu ced in such a calculation. We present constraints on the Standard and Two-Higgs-Doublet Model parameters coming from the measurement of b -- > s gamma decay. The current theoretical uncertainties do not allow on e to definitively restrict the Standard Model parameters much beyond t he limits coming from other experiments. The bounds on the Two-Higgs-D oublet 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 gamma, Z --> b (b) over bar and b --> c tau<(nu)over bar>(tau) processes are enough to give the most restrictive bounds in the M(H+/-)-tan beta plane.