Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A note on the GG-->PI 0 PI 0 reaction in the 1/N expansion of ChPT   In this work we present the results of a complete calculation of the $\gamma
  \gamma\rightarrow \pi^0\pi^0$ amplitude to leading order in the large $N$
approximation ($N$ being the number of Goldstone bosons) up to order
$m^2_{\pi}/F^2$. The amplitude turns to be proportional to that of
$\pi^+\pi^-\rightarrow \pi^0\pi^0$. In spite of the fact that this
factorization property cannot hold in general (as it was recently pointed out
by Morgan and Penington), it appears here since in the large $N$ limit only the
$I=J=0$ channel contributes to the $\gamma \gamma\rightarrow \pi^0\pi^0$
reaction. Moreover it seems to be a reasonable approximation in
  this case since it is possible to reproduce, as a prediction, the
experimental data starting from a one-parameter fit of the $\pi\pi$ scattering
data.

17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat