Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generalized polarizabilities and the spin-averaged amplitude in virtual
  Compton scattering off the nucleon   We discuss the low-energy behavior of the spin-averaged amplitude of virtual
Compton scattering (VCS) off a nucleon.
  Based on gauge invariance, Lorentz invariance and the discrete symmetries, it
is shown that to first order in the frequency of the final real photon only two
generalized polarizabilities appear.
  Different low-energy expansion schemes are discussed and put into
perspective.

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The categories of this paper are: astro-ph
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: nlin
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
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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: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga