Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Checking the Burkardt sum rule for the Sivers function by model
  calculations   The Sivers mechanism gives rise to a non-zero average transverse momentum of
partons inside a transversely polarized target. According to a sum rule of
Burkardt this transverse momentum vanishes when summing over all partons. We
explicitly check the Burkardt sum rule by means of one-loop calculations for a
quark target in perturbative QCD and for a diquark spectator model of the
nucleon. In both cases the sum rule is fulfilled.

16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga