Summary

Within the present framework of field theory, a theory ``A'': ``the neutrino is a Majorana particle and its weak-interaction is characterised by Lagrangian eq.(7) (which is different from the one expected in standard model)'' and theory ``B'': ``the neutrino is a Weyl particle and the standard-model gauge sector is strictly valid'' are phenomenologically completely equivalent. Therefore - without a powerful theory like the standard model that quantitatively predicts the form of the neutrino weak interaction without any recourse to measured neutrino properties - to go from theory ``A'' to ``B'' is merely a change of designations. This is how the equivalence between Weyl and Majorana neutrinos became conventional wisdom. However, 25 years of impressive experimental confirmations of the standard model convinced most particle physicists that the gauge sector of future theories is quantitatively described by this theory to good approximation. Under this - now very plausible - assumption, theory ``B'' is realized in nature, i.e. Majorana's idea of hermitian fermion fields describing neutral fermions is not realized in nature for the neutrino. This is a nontrivial constraint on all future theories. I do not claim that a Majorana theory is inconsistent in any sense: I only say that experimental results happen to prefer a Weyl neutrino, without offering any theoretical reason why this should be so. The present paper does not contradict any publication in a refereed journal, because none analysed the formal proof of Weyl - Majorana equivalence under the assumption of quantitative validity of the standard model.
Acknowledgements I sincerely thank H.Haber, B.Kayser, W.Marciano and S.Pezzoni for extensive discussions and explanations.