Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative Energy Densities in Extended Sources Generating Closed Timelike
  Curves in General Relativity with and without Torsion   Near a spinning point particle in (2+1)-dimensional gravity (or near an
infinitely thin, straight, spinning string in 3+1 dimensions) there is a region
of space-time with closed timelike curves. Exact solutions for extended sources
with apparently physically acceptable energy-momentum tensors, have produced
the same exterior space-time structure. Here it is pointed out that in the case
with torsion, closed timelike curves appear only for spin densities so high
that the spin energy density is higher than the net effective energy density.
In models without torsion, the presence of closed time-like curves is related
to a heat flow of unphysical magnitude. This corroborates earlier arguments
against the possibility of closed timelike curves in space-time geometries
generated by physical sources.

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The categories of this paper are: bayes-an
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The categories of this paper are: econ
1
The categories of this paper are: cs
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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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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: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat