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 tanβ 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(μ→eγ)10^-11 and B(τ→μγ)10^-7, 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 τ→μγ becomes larger. We also discuss the difference between our case and the case of the minimal SU(5) grand unified theory.