Mutual cosideration of $b\to s\gamma$ and $\mu \to e\gamma$ in supersymmetric SO(10) grand unification

Abstract

We compare the branching ratios for $b\to s\gamma$ and $\mu \to e\gamma$ in terms of constraining the parameter space in supersymmetric SO(10) grand unification models where supersymmetry is broken softly near the Planck scale by generationally symmetric operators. We observe two general cases. One with small $\tan \beta =2$ and the other one with large $\tan \beta$ having third generation Yukawa coupling unification at the GUT scale. \newline\indent We show that for small $\tan \beta$ the branching ratio constraints allow only a smaller region of parameter space for $\mu >0$ compared to $\mu <0$ for gluino mass $\text{alt}$ 500 GeV. With large $\tan \beta$, we find acceptable regions of parameter space with $\left|\mu \right|\text{alt}1$ TeV only for $\mu <0$. The dominant constraint on large $\tan \beta$ with $\mu >0$ parameter space is found to be given by the $b\to s\gamma$ branching ratio, while for large $\tan \beta$ with $\mu <0$ it is found to be given by the $\mu \to e\gamma$ branching ratio. In many of these acceptable regions, we find that the $\mu \to e\gamma$ branching ratio is predicted to be within one order of magnitude of its current experimental bound. We also show that the usually neglected gluino mediated diagrams in $b\to s\gamma$ can not be ignored in some regions of parameter space, especially for large $\tan \beta$ scenarios when the gluino mass is near its lower experimental bound.

Comments: 14 pages (Latex), 4 PS figs (uuencoded, epsf.tex), slight modification in text, as to appear in Physics Letters B