Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The chirally-odd twist-3 distribution e(x)   Properties of the nucleon twist-3 distribution function e(x) are reviewed. It
is emphasized that the QCD equations of motion imply the existence of a
delta-function at x=0 in e(x), which gives rise to the pion-nucleon sigma-term.
According to the resulting ``practical'' DIS sum rules the first and the second
moment of e(x) vanish, a situation analogue to that of the pure twist-3
distribution function $\bar{g}_2(x)$.

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The categories of this paper are: cond-mat
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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-alg
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The categories of this paper are: stat
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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: astro-ph
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The categories of this paper are: cs
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The categories of this paper are: chem-ph