Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: U_A(1) Problems and Gluon Topology - Anomalous Symmetry in QCD   Many of the distinctive and subtle features of the dynamics in the $U_A(1)$
channel in QCD can be related to gluon topology, more precisely to the
topological susceptibility $\chi(k^2) = i\int d^4x~e^{ikx}< 0|T~Q(x)~Q(0)|0>$,
where $Q = {\a_s\over8\pi} {\rm tr} G_{\m\n} \tilde G^{\m\n}$ is the gluon
topological charge density. The link is the $U_A(1)$ axial (ABJ) anomaly. In
this lecture, we describe the anomalous $U_A(1)$ chiral Ward identities in a
functional formalism and show how two apparently unrelated `$U_A(1)$ problems'
-- the mass of the $\eta'$ and the violation of the Ellis-Jaffe sum rule in
polarised deep-inelastic scattering -- can be explained in terms of the gluon
topological susceptibility. They are related through a $U_A(1)$ extension of
the Goldberger-Treiman formula, which is derived here for QCD with both
massless and massive quarks.

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The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg
9
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: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: plasm-ph
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The categories of this paper are: math-ph
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The categories of this paper are: physics
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The categories of this paper are: bayes-an
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The categories of this paper are: gr-qc
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The categories of this paper are: math