Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological Charge of U(1) Instantons   Non-singular instantons are shown to exist on noncommutative R^4 even with a
U(1) gauge group. Their existence is primarily due to the noncommutativity of
the space. The relation between U(1) instantons on noncommutative R^4 and the
projection operators acting on the representation space of the noncommutative
coordinates is reviewed. The integer number of instantons on the noncommutative
R^4 can be understood as the winding number of the U(1) gauge field as well as
the dimension of the projection on the representation space.

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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: solv-int
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga