We classify the different neutrino-mass patterns arising in string-inspired GUT and supersymmetric GUT models based on the flipped SU(5) ® U(1) and the SU( 4) ® 0( 4) gauge groups. Phenomenologically interesting spectra are obtained through the interplay of the two seesaw mechanisms present, with typical neutrino masses,...., 10-3 eV in the supersymmetric GUT models and of order 0.1-10 KeV in the ordinary GUTs.
The combined Fritzsch-Stech model for quarks is consistent with our present knowledge of quark masses and mixing angles. A possible way to extend it to leptons-by using an SOilO) framework-has been suggested by Bottino, Kim, Nishiura, and Sze. We investigate this model further and find some new features. It is first noted that the allowed quark masses are somewhat sensitive to the experimental uncertainties in the input parameters. This is carefully analyzed and we find that the original Stech Ansatz for the hadron sector is consistent. However, if the top-quark mass is greater than about 45 GeV, this Ansatz must be slightly modified. It is found that in a model of the present type the seesaw mechanism for neutrino masses may be drastically modified. This occurs because in SO(10) it is likely that the matrix of heavy "right-handed" neutrinos is close to a singular matrix. This feature is analyzed both analytically and numerically. Various patterns involving two extremely light neutrinos and one intermediate-mass (order of several MeV) neutrino which may arise are compared with experiment. More orthodox and perhaps more probable patterns for neutrino masses are also discussed. The lepton-mixing matrices are predicted and the results support recent explanations of the solar-neutrino paradox. -FRITZSCH-STECH MODEL IN SO( 10) 283
Science and Engineering Research Council 'The Science and Engineering Research Council does not accept any responsibility for loss or damage arising from the use of information contained in any of its reports or in any communication about its tests or investigations" RAL-92-035 A novel scenario for Neutrino Masses in Superstring-inspired GUT Models.
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