Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: From GLC to double-null coordinates and illustration with static black
  holes   We present a system of coordinates deriving directly from the so-called
Geodesic Light-Cone (GLC) coordinates and made of two null scalars intersecting
on a 2-dimensional sphere parameterized by two constant angles along geodesics.
These coordinates are shown to be equivalent to the well-known double-null
coordinates. As GLC, they present interesting properties for cosmology and
astrophysics. We discuss this latter topic for static black holes, showing
simple descriptions for the metric or particles and photons trajectories. We
also briefly comment on the time of flight of ultra-relativistic particles.

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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th