Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Drell-Yan production at small q_T, transverse parton distributions and
  the collinear anomaly   Using methods from effective field theory, an exact all-order expression for
the Drell-Yan cross section at small transverse momentum is derived directly in
q_T space, in which all large logarithms are resummed. The anomalous dimensions
and matching coefficients necessary for resummation at NNLL order are given
explicitly. The precise relation between our result and the
Collins-Soper-Sterman formula is discussed, and as a by-product the previously
unknown three-loop coefficient A^(3) is obtained. The naive factorization of
the cross section at small transverse momentum is broken by a collinear
anomaly, which prevents a process-independent definition of x_T-dependent
parton distribution functions. A factorization theorem is derived for the
product of two such functions, in which the dependence on the hard momentum
transfer is separated out. The remainder factors into a product of two
functions of longitudinal momentum variables and x_T^2, whose
renormalization-group evolution is derived and solved in closed form. The
matching of these functions at small x_T onto standard parton distributions is
calculated at O(alpha_s), while their anomalous dimensions are known to three
loops.

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The categories of this paper are: econ
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
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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: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: hep-ex
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The categories of this paper are: astro-ph
1
The categories of this paper are: cs
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The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
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The categories of this paper are: ao-sci