2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/45667The neutrino mass problem in $SU(4) \times SU(2)_{L} \times SU(2)_{R}$ SUSY GUT obtained from the compactification of $E_{8} \times E_{8}$ heterotic string is analyzed. The estimated values of the neutrino masses and mixing angles can explain the experimental data on solar neutrino flux.Latex file, 14 pagesHigh Energy Physics - Phenomenologytext