A global U(1)A symmetry is automatically embedded in the SU(11) model of Georgi which is the only known flavor unification with exactly 45 chiral fermions. The Higgs-field representations are 165's, 462's, and an adjoint. The U(1)A symmetry locates the ordinary fermions. Spontaneous breaking of U(1)A results in an invisible axion and Majorana masses of neutrinos of order {}0.1-1 eV.
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Jihn E. Kim (1981) studied this question.
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