= Massless two-flavor QCD symmetries
{title2=$SU(2)_L\times SU(2)_R\times U(1)_V$}
The <gauge-covariant kinetic term> for two massless <quarks> separates into left- and right-handed parts. Independent constant unitary <quark flavor> rotations preserve these terms, giving classical $U(2)_L\times U(2)_R$ internal <symmetry> in addition to local color $SU(3)$. The singlet axial $U(1)_A$ has a <chiral anomaly>, while the nonsinglet <chiral symmetry> and vector <baryon number> remain exact quantum symmetries, up to their shared discrete identifications. Equal nonzero <quark masses> reduce the continuous <flavor symmetry> to $SU(2)_V\times U(1)_V$.
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