Abstract
It is shown that the flavor-changing neutral current interaction of leptoquark exchange can be strongly suppressed by a global family symmetry without a numerical fine-tuning of the parameters. In the symmetry limit, if $n\ifmmode\times\else\texttimes\fi{}n$ degenerate leptoquarks couple universally to $n$ generations of quarks and leptons in the weak basis, not only is the neutral current interaction flavor diagonal, but also the charged current interaction takes exactly the same form as W exchange at low energies. Neutrino reactions and atomic parity violation still impose tight constraints. A quantitative analysis is made on the stability of flavor diagonalization and family independence against symmetry breaking due to the Higgs-Yukawa coupling. The mechanism is robust against symmetry breaking in the environment of the standard model.
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