Constraints on SUSY-GUT unification from $b\to s\gamma$ decay

The top-quark Yukawa infrared fixed-point solution of the renormalization group equations, with minimal supersymmetry and GUT unification, defines a low-energy spectrum of supersymmetric particle masses in terms of a few GUT-scale parameters assuming universal boundary conditions. We give predictions in this model for the inclusive $b\to s\gamma$ branching fraction and investigate the impact of non-universal scalar mass boundary conditions. We find our results do not depend significantly on the value of the GUT-scale trilinear coupling $A^G$. The small $\tan \beta$ region favors predictions for the inclusive $b\to s\gamma$ branching fraction close to that of the Standard Model value. Nevertheless forthcoming experimental results can eliminate some regions of the GUT parameter space.