Editing Chiral anomaly (section)

==Calculation==
The chiral anomaly can be calculated exactly by [[one-loop Feynman diagram]]s, e.g.  Steinberger's "triangle diagram", contributing to the [[pion]] decays,   and <math>\pi^0\to e^+e^-\gamma</math>. The amplitude for this process can be calculated directly from the change in the [[measure (physics)|measure]] of the fermionic fields under the chiral transformation.

Wess and Zumino developed a set of conditions on how the [[Partition function (quantum field theory)|partition function]] ought to behave under [[gauge transformation]]s called the '''Wess–Zumino consistency condition'''.

Fujikawa derived this anomaly using the correspondence between [[functional determinant]]s and the [[Partition function (quantum field theory)|partition function]] using the [[Atiyah–Singer index theorem]]. See [[Fujikawa's method]].