Generation of Neutrino Masses and Mixings in Gauge Theories

Recent experimental data of neutrinos make big impact on the neutrino masses and their mixings. Most exciting one is the results at Super-Kamiokande on the atmospheric neutrinos, which indicate the large neutrino flavor oscillation of νμ → νx . Solar neutrino data also provide the evidence of the neutrino oscillation, however this problem still uncertain . What can we learn from these results? We want to get clues for origins of neutrino masses and neutrino flavor mixings. In particular, we want to underatand why the neutrino mixing is large compared with the quark sector. Now we should discuss these problems in connection with the quark sector.