Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Breakdown of chiral expansion for parton distributions   In the framework of the chiral perturbation theory we computed two- and
three-loop corrections to the pion parton distributions which posses
$\delta$-function singularities at x->0. This calculation explicitly
demonstrates that in the region of small x ~ mpi^2/(4 pi F)^2 standard ChPT
breaks down and one needs resummation of all orders. We give an example of such
resummation.

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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
3
The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: math-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: econ