Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pion Photoproduction Amplitude Relations in the 1/N_c Expansion   We derive expressions for pion photoproduction amplitudes in the 1/N_c
expansion of QCD, and obtain linear relations directly from this expansion that
relate electromagnetic multipole amplitudes at all energies. The leading-order
relations in 1/N_c compare favorably with available data, while the
next-to-leading order relations seem to provide only a small improvement.
However, when resonance parameters are compared directly, the agreement at
O(1/N_c) or O(1/N_c^2) is impressive.

4
The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
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The categories of this paper are: stat
23
The categories of this paper are: solv-int