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A flavor-changing neutral current changes fermion flavor without changing electric charge. Such currents are absent at tree level in the Standard Model and are strongly suppressed at loop level by the <Glashow-Iliopoulos-Maiani mechanism>.


Flavor-changing neutral current

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The Glashow-Iliopoulos-Maiani mechanism uses the unitarity of the quark mixing matrix to cancel flavor-changing neutral-current amplitudes when equal-charge quark masses are degenerate. The remaining loop amplitudes are suppressed by quark-mass differences.


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 Incoming links: Glashow-Iliopoulos-Maiani mechanism