We discuss 2-cocycles of the Lie algebra $Map(M^3;g)$ of smooth, compactly supported maps on 3-dimensional manifolds $M^3$ with values in a compact, semi-simple Lie algebra $g$. We show by explicit calculation that the Mickelsson-Faddeev-Shatashvili cocycle $f{ii}{24pi^2}inttrac{Accr{dd X}{dd Y}}$ is cohomologous to the one obtained from the cocycle given by Mickelsson and Rajeev for an abstract Lie algebra $gz$ of Hilbert space operators modeled on a Schatten class in which $Map(M^3;g)$ can be naturally embedded. This completes a rigorous field theory derivation of the former cocycle as Schwinger term in the anomalous Gauss law commutators in chiral QCD(3+1) in an operator framework. The calculation also makes explicit a direct relation of Connes non-commutative geometry to (3+1)-dimensional gauge theory and motivates a novel calculus generalizing integration of $g$-valued forms on 3-dimensional manifolds to the non-commutative case.
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