Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Invariant amplitudes for coherent electromagnetic pseudoscalar
  production from a spin-one target   A set of 13 linearly independent invariant amplitudes for the electromagnetic
production of a pseudoscalar particle from a spin-one particle is derived which
respect Lorentz and gauge invariance. The $T$-matrix can be represented by a
linear superposition of these amplitudes with invariant functions as
coefficients, which depend on the Mandelstam variables only. Their explicit
form is determined by the underlying dynamics. Nine of these amplitudes are
purely transverse and describe photoproduction. The remaining four appear in
electroproduction in addition, describing charge and longitudinal current
contributions. Furthermore, a reduction of these amplitudes to operators acting
in non-relativistic spin space is given.

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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th