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キーワード:
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要旨:
We study non-minimal variants of the seesaw mechanism, especially of the type I and the double seesaw mechanism, in correlation with a singular Majorana mass term in the neutrino mass matrix. Also we demonstrate that in the inverse
seesaw mechanism a “pseudo-singular” structure for the neutrino mass matrixcan be realized. It is further shown that in all scenarios under consideration active neutrino masses at the compulsory eV scale can be obtained in principle.
By analyzing the eigenvalue and mass scale structure of the neutrino mass matrix in the singular double seesaw we find scenarios that feature eV, keV and MeV to GeV sterile neutrinos..
