Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A theoretical approach to the (pion^{-}, gamma gamma) reaction in nuclei   We have studied the pion^{-} capture in nuclei leading to two photons, using
improved many body methods which have been tested with success in one photon
pion^{-} radiative capture, muon^{-} capture and neutrino scattering. The
qualitative features of the experimental data are reproduced but there are
still some disagreement at small relative photon angles. The reaction is a
potential source of information on details of the gamma-gamma-pion-pion vertex
where chiral corrections can be relevant. New and more precise experiments are
planned which make calculations like the present one relevant and opportune.
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28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc