A light sterile neutrino based on the seesaw mechanism

金沢大学理工研究域数物科学系We propose a simple model of the neutrino mass matrix that can explain the solar and atmospheric neutrino problems in a 3(vL+vR) framework. Assuming that only two righthanded neutrinos are heavy and a Dirac mass matrix has a special texture, we construct a model with four light neutrinos. The favorable structure of flavor mixings and mass eigenvalues required by these neutrino deficits is realized as a result of the seesaw mechanism. It is possible that bi-maximal mixing structure can be obtained in this scheme. Since it contains a light sterile neutrino, it may be capable of explaining the LSND result successfully. We consider an embedding of this scenario for the neutrino mass matrix into the SU(5) grand unification scheme using the Froggatt-Nielsen mechanism based on U(1)F1 × U(1)F2. In this case, only a large mixing angle MSW solution is obtained for the solar neutrino problem as a consistent solution