Flavor Symmetry
Flavor symmetry conjectures propose underlying symmetries governing the different quark and lepton flavors within the Standard Model, though their precise form remains elusive.
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The statement of the theorem
Let be a proposed flavor symmetry group acting on the flavor indices . The Lagrangian density must be invariant under this transformation: . This invariance implies that the mass matrices for quarks and leptons must transform covariantly under . Specifically, if is the mass matrix, then dictates that must be proportional to the identity matrix or satisfy specific relations derived from the symmetry generators : \n \nThis constrains the structure of the Yukawa couplings such that .
Source: Wikipedia