Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Axial anomaly and the precise value of the $\pi^0 \to 2 \gamma$ decay
  width   The anomaly in the vacuum expectation value of the product of axial and two
vector currents (AVV) in QCD is investigated. The goal is to determine from its
value the $\pi^0 \to 2 \gamma$ decay width with high precision. The sum rule
for AVV formfactor is studied. The difference $f_{\pi^0} - f_{\pi^+}$ caused by
strong interaction is calculated and appears to be small. The $\pi^0 - \eta$
mixing is accounted. The $\pi^0 \to 2 \gamma$ decay width determined
theoretically from the axial anomaly is found to be $\Gamma(\pi^0 \to 2 \gamma)
= 7.93 eV$ with an error $\sim 1.5%$. The measurement of the $\pi^0 \to 2
\gamma$ decay width at the same level of accuracy would allow one to achieve a
high precision test of QCD.

31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
24
The categories of this paper are: dg-ga