Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quark Model Calculations Of Symmetry Breaking in Parton Distributions   Using a quark model, we calculate symmetry breaking effects in the valence
quark distributions of the nucleon. In particular, we examine the breaking of
the quark model SU(4) symmetry by color magnetic effects, and find that color
magnetism provides an explanation for deviation of the ratio $d_V(x)/u_V(x)$
from $1/2$. Additionally, we calculate the effect of charge symmetry breaking
in the valence quark distributions of the proton and neutron and find, in
contrast to other authors, that the effect is too small to be seen
experimentally.

33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an