Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Photon Structure Function $F_2$ in QCD with Nonlocal Vacuum Quark
  Condensates   We calculate the contribution from nonlocal vacuum condensates of quark
fields to the hadronic part of the photon structure function $F_2(x)$ in the
operator product expansion approach to QCD. The result is a smooth function of
$x$ and its magnitude is comparable with one of gluon condensate. Extrapolation
to the case of real photon is realized with the help of the model, suggested by
Gorsky et al. As a result we obtain a substantial improvement of the agreement
with experimental data for the standard value of the parameter $\lambda_q^2
\equiv \langle\bar qD^2 q\rangle /\langle\bar qq\rangle \approx 0.5 \ \ GeV^2
$.}

5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn