Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Slowly rotating fluid balls with linear equation of state   Slowly rotating perfect fluid balls with regular center and asymptotically
flat exterior are considered to second order in the rotation parameter. The
necessary condition for being Petrov type D is given for general perfect fluid
matter. As a special case, fluids with a linear equation of state are
considered. Using a power series expansion at the regular center, it is shown
that the Petrov D condition is inconsistent with the linear equation of state
assumption.

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The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: astro-ph
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
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The categories of this paper are: econ