Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sigma Terms of Light-Quark Hadrons   A calculation of the current-quark mass dependence of hadron masses can help
in using observational data to place constraints on the variation of nature's
fundamental parameters. A hadron's sigma-term is a measure of this dependence.
The connection between a hadron's sigma-term and the Feynman-Hellmann theorem
is illustrated with an explicit calculation for the pion using a rainbow-ladder
truncation of the Dyson-Schwinger equations: in the vicinity of the chiral
limit sigma_pi = m_pi/2. This truncation also provides a decent estimate of
sigma_rho because the two dominant self-energy corrections to the rho-meson's
mass largely cancel in their contribution to sigma_rho. The truncation is less
accurate for the omega, however, because there is little to compete with an
omega->rho+pi self-energy contribution that magnifies the value of sigma_omega
by ~25%. A Poincare' covariant Faddeev equation, which describes baryons as
composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain
the current-quark mass dependence of the masses of the nucleon and Delta, and
thereby sigma_N and sigma_Delta. This "quark-core" piece is augmented by the
"pion cloud" contribution, which is positive. The analysis yields sigma_N~60MeV
and sigma_Delta~50MeV.

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The categories of this paper are: physics
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: atom-ph
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an