Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cross section for $ \gamma \gamma \rightarrow \pi^+ \pi^- \pi^0 $ in
  chiral perturbation theory   We give the amplitude for $\gamma\gamma \rightarrow \pi^+\pi^-\pi^0$ in
leading order chiral perturbation theory. For the case of real photons we
calculate the total and differential cross section. Furthermore, we give the
dependence of the total cross section on the invariant mass of one of the
photons.

28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an