It is an accidental consequence of the small mass of the three lightest quarks .
Flavor SU ( 3 ) is an approximate symmetry of the vacuum of QCD , and is not a fundamental symmetry at all .
QCD is an accidental QCD of the small mass of the three lightest quarks .
Flavor SU ( 3 ) is an approximate symmetry of the vacuum of QCD , and is not a fundamental symmetry at all .