= Zero flavour triality of a light-quark hadron
{title2=$a+2b\equiv0\pmod3$}
For a <colour singlet> <hadron> built entirely from <up quarks>, <down quarks>, <strange quarks>, <antiquarks> and <gluons>, the net number of quarks is a multiple of three. The central <SU(3)> colour element multiplies the state by $\omega^{n_q-n_{\bar q}}$, while a singlet must be unchanged. The central flavour element supplies the same phase because all three light flavours form the fundamental representation. Every resulting flavour multiplet therefore has zero <SU(3) triality>. <Heavy quarks> are singlets of light-flavour SU(3), so hadrons containing them do not obey this argument. The zero-triality restriction allows higher light-quark multiplets as well as the familiar singlet, octet and decuplet.
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