Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global regular null hypersurfaces in a perturbed Schwarzschild black
  hole exterior   The spherically symmetric null hypersurfaces in a Schwarzschild spacetime are
smooth away from the singularities and foliate the spacetime. We prove the
existence of more general foliations by null hypersurfaces without the
spherical symmetry condition. We show that nearly round null hypersurfaces can
be extended regularly to the past null infinity in a Schwarzschild spacetime.
In fact we also relax the spherical symmetry of the ambient spacetime and prove
a more general result: in a perturbed Schwarzschild spacetime (not necessary
being vacuum), nearly round null hypersurfaces can be extended regularly to the
past null infinity, thus there exist many foliations by regular null
hypersurfaces in the exterior region of a perturbed Schwarzschild black hole.

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The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
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The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: q-alg
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The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph
1
The categories of this paper are: cs
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The categories of this paper are: alg-geom