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Dark matter in the supersymmetric radiative seesaw model with an anomalous U(1) symmetry

The existence of an anomalous U(1) symmetry is shown to play a crucial role in the supersymmetric radiative seesaw model for neutrino masses. It explains the smallness of some couplings related to neutrino mass generation in a favorable way in addition to cause the hierarchical structure of Yukawa couplings of quarks and leptons. If it is spontaneously broken to a $Z_2$ subgroup, this $Z_2$ symmetry can make a lifetime of the lightest field with its odd parity extremely long. Thus, the model has an additional dark matter candidate other than the lightest neutralino, which appears in the $R$-parity conserved MSSM. We discuss the nature of dark matter by taking account of its relation to the neutrino mass generation and the lepton flavor violation.