Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Threshold Pion Electroproduction in Chiral Perturbation Theory   Electroproduction of pions on the nucleon near the threshold is analyzed
within the framework of baryon chiral perturbation theory. We give a thorough
discussion of the low--energy theorems related to charged and neutral
electropionproduction. It is shown how the axial radius of the nucleon can be
related to the S--wave multipoles $E_{0+}^{(-)}$ and $L_{0+}^{(-)}$. The chiral
perturbation theory calculations of the $\gamma^\star p \to \pi^0 p$ reaction
are found to be in good agreement with the recent near threshold data. We also
discuss the influence of some isospin--breaking effects in this channel. For
future experimental tests of the underlying chiral dynamics, extensive
predictions of differential cross sections and multipole amplitudes are
presented.

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The categories of this paper are: math-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio