We analyze lepton flavor violating $\tau \to \mu \gamma$ and $\mu \to e\gamma$ processes in a supersymmetric grand unified theory model in which sfermions have a special mass spectrum. It is assumed that only third generation sfermions which are contained in $\mathbf{10}(\mathrm{Q},{\mathrm{U}}^{\mathrm{c}},{\mathrm{E}}^{\mathrm{c}})$ of SU(5) can have a different mass from the others. This mass spectrum is derived from the ${\mathrm{E}}_6$ grand unified theory model with horizontal symmetries. It is shown that branching ratios of $\tau \to \mu \gamma$ and $\mu \to e\gamma$ depend strongly on a right-handed stau mass. The weak scale stability requires a light stau, so large decay rates can be expected in this scenario. When the stau mass is around 150 GeV and $\tan \beta \sim 10$, the branching ratios can be larger than $\mathrm{Br}(\tau \to \mu \gamma )\simeq {10}^{-8}$ and $\mathrm{Br}(\mu \to e\gamma )\simeq 5\times {10}^{-12}$, which are within reach of future experiments. In addition, this model has an interesting feature that the final state charged lepton tends to have right-handed chirality.

• Received 11 January 2007

DOI:https://doi.org/10.1103/PhysRevD.75.115008