The Effect of Supersymmetric Particles on b -> s \gamma Decay in Supergravity Models

The effect of loops involving charginos with up-type squarks, and gluinos with down-type squarks, on the inclusive decay mode $b\to s\gamma$ is studied in the context of minimal $N=1$ Supergravity models with a radiatively broken electroweak symmetry group. It is confirmed that the strong constraints imposed by the CLEO upper bound $B(b\to s\gamma )<5.4\times {10}^{-4}$ on two-Higgs doublets models are much weaker in supersymmetric theories due to partial cancelations from loops involving charginos and up-type squarks. The dependence of the branching ratio and the supersymmetry masses on the top quark mass is explored.