Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chiral expansion of the $\pi^0\rightarrow\gamma\gamma$ decay width   A chiral field theory of mesons has been applied to study the contribution of
the current quark masses to the $\pi^0\rightarrow\gamma\gamma$ decay width at
the next leading order. $2\%$ enhancement has been predicted and there is no
new parameter.

27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an