Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Charge Symmetry Breaking Effects in Pion and Kaon Structure   Charge symmetry breaking (CSB) effects associated with the $u$ and $d$ quark
mass difference are investigated in the quark distribution functions and
spacelike electromagnetic form factors of the pion and kaon. We use a confining
version of the Nambu--Jona-Lasinio model, where CSB effects at the infrared
scale associated with the model are driven by the dressed $u$ and $d$ quark
mass ratio, which because of dynamical chiral symmetry breaking is much closer
to unity than the associated current quark mass ratio. The pion and kaon are
given as bound states of a dressed quark and a dressed antiquark governed by
the Bethe-Salpeter equation, and exhibit the properties of Goldstone bosons,
with a pion mass difference given by $m_{\pi^+}^2 - m_{\pi^0}^2 \propto (m_u -
m_d)^2$ as demanded by dynamical chiral symmetry breaking. We find significant
CSB effects for realistic current quark mass ratios ($m_u/m_d \sim 0.5$) in the
quark flavor-sector electromagnetic form factors of both the pion and kaon. For
example, the difference between the $u$ and $d$ quark contributions to the
$\pi^+$ electromagnetic form factors is about 8\% at a momentum transfer of
$Q^2 \simeq 10\,$GeV$^2$, while the analogous effect for the light quark sector
form factors in the $K^+$ and $K^0$ is about twice as large. For the Parton
distribution functions, we find CSB effects which are considerably smaller than
those found in the electromagnetic form factors.

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The categories of this paper are: quant-ph
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The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: eess
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
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The categories of this paper are: econ
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th