Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutral pion photoproduction on protons in fully covariant ChPT with
  Delta(1232) loop contributions   We study the neutral pion photoproduction at near-threshold energies in fully
covariant chiral perturbation theory up to O(p^3). When including only
nucleonic virtual states in the model, the convergence is too slow. Therefore
we test the model when introducing the Delta(1232) resonance as an additional
degree of freedom. Some low-energy constants were fitted, converging to values
in good agreement with those expected from literature.

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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: physics
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn