The Neutrino Mass Spectrum in the Supersymmetric Flipped SU(5)xU(1) GUT Model

In the context of the supersymmetric flipped $SU(5)\otimes U(1)$ GUT model, we have studied in detail the neutrino mass spectrum, obtaining an approximate formula for the corresponding effective three-generation mass matrix. It is found that at least two neutrinos are expected to have extremely small masses of no particular interest. The third neutrino, on the other hand, may eventually get a mass of order ${10}^{-3}$ eV, of relevance for the solution of the solar neutrino problem with the MSW mechanism, as a consequence of vacuum-expectation-values at the GUT mass scale for some of the scalar partners of the right-handed neutrinos.