Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A simple characterization of generalized Robertson-Walker spacetimes   A generalized Robertson-Walker spacetime is the warped product with base an
open interval of the real line endowed with the opposite of its metric and base
any Riemannian manifold. The family of generalized Robertson-Walker spacetimes
widely extends the one of classical Robertson-Walker spacetimes. In this
article we prove a very simple characterization of generalized Robertson-Walker
spacetimes; namely, a Lorentzian manifold is a generalized Robertson-Walker
spacetime if and only if it admits a timelike concircular vector field.

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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
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The categories of this paper are: econ
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: q-alg
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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio