Lepton-flavor violation via right-handed neutrino Yukawa couplings in the supersymmetric standard model

Various lepton-flavor-violating (LFV) processes in the supersymmetric standard model with right-handed neutrino supermultiplets are investigated in detail. It is shown that large LFV rates are obtained when $tan\beta$ is large. In the case where the mixing matrix in the lepton sector has a similar structure as the Kobayashi-Maskawa matrix and the third-generation Yukawa coupling is as large as that of the top quark, the branching ratios can be as large as $B(\mu \to e\gamma )\simeq {10}^{-11\mathrm{}}$ and $B(\tau \to \mu \gamma )\simeq {10}^{-7\mathrm{}}$, which are within the reach of future experiments. If we assume a large mixing angle solution to the atmospheric neutrino problem, the rate for the process $\tau \to \mu \gamma$ becomes larger. We also discuss the difference between our case and the case of the minimal SU(5) grand unified theory.