b to s γ Decay and Supersymmetry

The inclusive radiative $B$-decay is a sensitive probe of new physics, especially if related to the virtual exchange of a charged Higgs boson. Supersymmetric models provide a particularly interesting example. In the limit of exact supersymmetry, BR($b \to s\gamma$)~=~0, due to the vanishing of any magnetic-moment transition operator. We illustrate the impact of this constraint for realistic values of the supersymmetry-breaking parameters.