Suppose the simple theory with chiral fermions possessing non-trivial gauge anomalies cancellation (it is given here):
S=∫d4x(ˉψiγμDμψψ+ˉκiγμDμκκ),
where
Dμψ=∂μ−iAμLPL−iAμRPR,Dμκ=∂μ+iAμLPL+iAμRPR
Although separately
ψ,κ sectors are anomalous, together their gauge anomalies are cancelled:
∂μJμL/R,ψ,κ=±196π2ϵμναβFL/RμνFL/Rαβ,∂μ(JμL/R,ψ−JμL/R,κ)=0
Lets generate the mass for
κ fermion (by using spontaneous symmetry breaking with higgs singlet
feiφ with infinite mass for
f) and integrate it out in the limit
mκ→∞. Corresponding effective field theory has to be free from anomalies, so there must be (possibly non-local) a term
Γ[AL,AR,φ] reproducing the anomalous structure of the
κ sector; it is called the Wess-Zumino term. It is possible to write it explicitly, and it turns out that this it is
local (a polynomial in
A,φ and their derivatives):
ΓWZ=124π2∫d4xϵμναβ(ALμARν∂αALβ+ALμARν∂αARβ+
+φf(∂μALν∂αALβ+∂μARν∂αARβ+∂μALν∂αARβ))
However, as I know, the anomaly (at least in theories with chiral fermions) is the local expression given by the variation of the non-local action. So where the non-locality is hidden?