2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/212877The existence of the mirror world, with the same microphysics as our own one but with opposite P-asymmetry, not only restores an exact equivalence between left and right but also naturally explains, via a see-saw like mechanism, why the neutrino is ultralight.8 pages, LaTex. Revised version, now identical with the journal publicationHigh Energy Physics - Phenomenologytext