Constraints on the minimal supergravity model from the b-->s gamma decay.

Abstract

The constraints on the minimal supergravity model from the b\ensuremath{\rightarrow}s\ensuremath{\gamma} decay are studied. A large domain in the parameter space for the model satisfies the CLEO bound B(b\ensuremath{\rightarrow}s\ensuremath{\gamma})5.4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$. However, the allowed domain is expected to diminish significantly with an improved bound on this decay. The dependence of the b\ensuremath{\rightarrow}s\ensuremath{\gamma} branching ratio on various parameters is studied in detail. It is found that, for ${\mathit{A}}_{\mathit{t}}$0 and the top quark mass within the vicinity of the center of the CDF value ${\mathit{m}}_{\mathit{t}}^{\mathrm{pole}}$=174\ifmmode\pm\else\textpm\fi{}17 GeV, there exists only a small allowed domain because the light top squark is tachyonic for most of the parameter space. A similar phenomenon exists for a lighter top and ${\mathit{A}}_{\mathit{t}}$ negative when the GUT coupling constant is slightly reduced. For ${\mathit{A}}_{\mathit{t}}$>0, however, the branching ratio is much less sensitive to small changes in ${\mathit{m}}_{\mathit{t}}$ and ${\mathrm{\ensuremath{\alpha}}}_{\mathit{G}}$.