Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Matter shear and vorticity in conformally flat spacetimes   In this paper we consider conformally flat perturbations on the Friedmann
Lemaitre Robertson Walker (FLRW) spacetime containing a general matter field.
Working with the linearised field equations, we unearth some important
geometrical properties of matter shear and vorticity and how they interact with
the thermodynamical quantities in the absence of any free gravity powered by
the Weyl curvature. As there are hardly any physically realistic rotating exact
conformally flat solutions in general relativity, these covariant and gauge
invariant results bring out transparently the role of vorticity in the
linearised regime. Most interestingly, we demonstrate that the matter shear
obeys a transverse traceless tensor wave equation, and the vorticity obeys a
vector wave equation in this regime. These shear and vorticity waves replace
the gravitational waves in the sense that they causally carry the information
about local change in the curvature of these spacetimes.

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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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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: ao-sci
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: cs
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an