Massless neutrinos in left-hand symmetric models

Abstract We present an alternative to the Yanagida-Gell-Mann-Ramond-Slansky method of obtaining small neutrino masses in spite of normal Dirac mass terms in left-right symmetric theories. In our scheme, the light neutrinos remain massless while there exist massive Dirac neutral leptons in each generation. The masses of these are determined by the scale of left-right symmetry breaking which must be large enough to prevent flavour-changing processes such as μ → eγ.