There are three families of fermions, each consisting of the representations, (q for left-handed quark), (dc for the left-handed anti d-quark), (uc for the left handed up antiquark), (l for the left handed leptons), (ec for the left-handed positron) and (νc for the left-handed antineutrino, which is now known to exist. See Neutrino oscillation.).
Of course, calling the representations things like is purely a physicist's convention, not a mathematician's convention, where representations are either labelled by Young tableaux or Dynkin diagrams with numbers on their vertices, but still, it is standard among high energy physicists.
Since the homotopy group
The Yukawa couplings of the scalar Higgs fields with the fermions produces the fermion masses after the Higgs field acquires a VEV.
See also Grand unified theory.
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