Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The decoupling problem of the Proca equation; and treatment of Dirac,
  Maxwell and Proca fields on the resulting pp-wave spacetimes   In this work we take a formal approach to the problem of decoupling Proca
equations in curved space-times. We use Newman-Penrose (NP) two-spinor
formalism to represent the Proca vector by one complex and two real scalars. We
show that a decoupled second order differential equation for one of the real
scalars can be derived if and only if the background space-time admits a
covariantly constant null vector. Thus, the background space-time must be a
pp-wave vacuum. We evaluate the separability of Proca, Maxwell and Dirac
equations on the resulting pp-wave background.

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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: cond-mat