Probing physics beyond the standard model from lepton sector

The Standard Model (SM) is the most successful model to explain physics below the weak scale. The recent results for sin 2β or sin 2φ1 by Belle [1] and Babar [2] are converging, and they are consistent with the Kobayashi-Maskawa mechanism [3]. Also, the precision measurements of the electroweak parameters suggest the light SM Higgs boson such as mh ∼ 196GeV (95%CL) [4]. Now we are waiting for signature of physics beyond the SM. We have the clue for the physics beyond the SM in the neutrino oscillation experiment results. The atmospheric neutrino result by the superKamiokande experiment is established [5]. The combined result of the superKamiokande [6] and SNO [7] experiments shows a strong evidence for the appearance of νμ or ντ in the solar neutrino. At present, the large-angle MSW solution is the most favored, which will be checked by the Kamland experiment soon [8]. These neutrino oscillation results can be explained by introduction of small neutrino masses. Introduction of small neutrino masses gives us a new scenery for physics beyond the SM.While the promising candidate for origin of the small neutrino masses is the see-saw mechanism [9] by introduction of the right-handed neutrinos, the atmospheric neutrino result implies that the righthanded neutrino mass should be smaller than ∼ 10GeV, which is much smaller than the Planck scale. This is a good motivation for introduction of Supersymmetry (SUSY). A quadraticallydivergent contribution to the Higgs boson mass proportional to the right-handed neutrino masses should be canceled even if the correction proportional to the Planck mass is vanishing by some mysterious physics. Nowadays, the minimal supersymmetric standard model (MSSM) is one the most promising extension of standard model (SM), and many experiments are searching for the possible evidence of the low-energy supersymmetry. In this review we discuss the possibilities in physics of charged lepton, paying attention to the dipole-moment operators; L = elj 2 l̄iσμνF (LijPL +RijPR)lj (1)