Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Behaviour of Non--Singlet Structure Functions at Small $x$   The resummation of $O(\alpha_s^{l+1} \ln^{2l} x)$ terms in the evolution
kernels of non--singlet combinations of unpolarized and polarized structure
functions is investigated. The agreement with complete calculations up to order
$\alpha_s^2$ is demonstrated, and the leading small-$x$ contributions to the
three--loop non--singlet splitting functions $P^{\pm}$ are derived. The
additional contributions due to the resummed terms are studied numerically for
the most important non--singlet structure functions. They are found to be about
$1\,\%$ or smaller in the kinematical regions accessible at present and in the
foreseeable future.

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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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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: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph