2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/199209Assuming that the neutrino mass matrix is dominated by a term with the permutation symmetry $S_{\scriptscriptstyle 3}$ it is possible to explain neutrino data only if the masses are quasi-degenerate. A sub-dominant term with an approximate $μ-τ$ symmetry leads to an approximate tri-bimaximal form. Experimental consequences are discussed.7 pages, 2 figures, 1 table, RevTexHigh Energy Physics - Phenomenologytext