Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gauge fields and particle-like formations associated with shear-free
  null congruences   We consider Maxwell fields associated with any shear-free null geodesic
congruence on Minkowski or Riemannian background space-time. Bounded singular
loci of these fields are treated as particle-like formations, possess
"self-quantized" electric charge and undergo self-consistent time dynamics.
Complicated singular solutions of Maxwell (as well as related complex
Yang-Mills) equations can be obtained in a purely algebraic way using the Kerr
theorem.

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The categories of this paper are: nucl-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess