> The Standard Model does not explain neutrino mass Not as originally formulated (because back then neutrinos were thought to be massless) but it's straightfor

> The Standard Model does not explain neutrino mass Not as originally formulated (because back then neutrinos were thought to be massless) but it's straightforward to extend that original version to include neutrino masses, by giving leptons their own equivalent to the quark sector's CKM matrix [1], the PMNS matrix [2]. In modern parlance, "Standard Model" means this updated version. Granted, if you do just that, you make neutrinos Dirac spinors (just like the quarks) and there is no obvious reason for why they should be so much lighter than the other fermions. Giving them a Majorana mass induced by a much heavier (GUT-scale) equivalent to the Standard Model Higgs would provide a natural explanation for that mass hierarchy through the seesaw mechanism [3], and that would be true Beyond the Standard Model physics. [1] https://en.wikipedia.org/wiki/Cabibbo–Kobayashi–Maskawa_matrix https://en.wikipedia.org/wiki/Cabibbo–Kobayashi–Maskawa_matr... [2] https://en.wikipedia.org/wiki/Pontecorvo–Maki–Nakagawa–Sakata_matrix https://en.wikipedia.org/wiki/Pontecorvo–Maki–Nakagawa–Sakat... [3] https://en.wikipedia.org/wiki/Seesaw_mechanism https://en.wikipedia.org/wiki/Seesaw_mechanism