Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nucleon matrix elements of higher-twist operators from the instanton
  vacuum   We compute the nucleon matrix elements of QCD operators of twist 3 and 4 in
the instanton vacuum. We consider the operators determining 1/Q^2-power
corrections to the Bjorken, Ellis-Jaffe and Gross-Llewellyn-Smith sum rules.
The nucleon is described as a soliton of the effective chiral theory derived
from instantons in the 1/N_c-expansion. QCD operators involving the gluon field
are systematically represented by effective operators in the effective chiral
theory. We find that twist-3 matrix elements are suppressed relative to twist-4
by a power of the packing fraction of the instanton medium. Numerical results
for the spin-dependent (d^(2), f^(2)) and spin-independent twist-3 and 4 matrix
elements are compared with results of other approaches and with experimental
estimates of power corrections. The methods developed can be used to evaluate a
wide range of matrix elements relevant to DIS.

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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: astro-ph
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-th
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The categories of this paper are: physics
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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: chem-ph
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The categories of this paper are: cmp-lg