Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dynamical Coupled-Channels Effects on Pion Photoproduction   The electromagnetic pion production reactions are investigated within the
dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193
(2007)}. The meson-baryon channels included in this study are $\gamma N$, $\pi
N$, $\eta N$, and the $\pi\Delta$, $\rho N$ and $\sigma N$ resonant components
of the $\pi\pi N$ channel. With the hadronic parameters of the model determined
in a recent study of $\pi N$ scattering, we show that the pion photoproduction
data up to the second resonance region can be described to a very large extent
by only adjusting the bare $\gamma N \to N^*$ helicity amplitudes, while the
non-resonant electromagnetic couplings are taken from previous works. It is
found that the coupled-channels effects can contribute about 10 - 20 % of the
production cross sections in the $\Delta$ (1232) resonance region, and can
drastically change the magnitude and shape of the cross sections in the second
resonance region. The importance of the off-shell effects in a dynamical
approach is also demonstrated. The meson cloud effects as well as the
coupled-channels contributions to the $\gamma N \to N^*$ form factors are found
to be mainly in the low $Q^2$ region. For the magnetic M1 $\gamma N \to \Delta$
(1232) form factor, the results are close to that of the Sato-Lee Model.
Necessary improvements to the model and future developments are discussed.

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The categories of this paper are: econ
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: astro-ph
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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga