Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Second and higher-order perturbations of a spherical spacetime   The Gerlach and Sengupta (GS) formalism of coordinate-invariant, first-order,
spherical and nonspherical perturbations around an arbitrary spherical
spacetime is generalized to higher orders, focusing on second-order
perturbation theory. The GS harmonics are generalized to an arbitrary number of
indices on the unit sphere and a formula is given for their products. The
formalism is optimized for its implementation in a computer algebra system,
something that becomes essential in practice given the size and complexity of
the equations. All evolution equations for the second-order perturbations, as
well as the conservation equations for the energy-momentum tensor at this
perturbation order, are given in covariant form, in Regge-Wheeler gauge.

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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: eess
7
The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: nlin
0
The categories of this paper are: hep-ph