2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/86671This encyclopedia article addresses questions like the following. How does the Sun shine? Does the neutrino have a mass? Are there weak interactions beyond those described by the standard model of particle physics?To appear in the 3rd edition of the Encyclopedia of Physics, eds. G. Trigg and R. Lerner (Wiley-VCH, Weinheim 2005)Physics EducationAstrophysicsHigh Energy Physics - PhenomenologyNuclear ExperimentGeneral Physicstext