Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An equation-of-state-insensitive measure of neutron star stiffness   Universal relations (i.e., insensitive to the equation of state) between
macroscopic properties of neutron stars (NSs) have proven useful for a variety
of applications -- from providing a direct means to extract observables from
data to breaking degeneracies that hinder tests of general relativity.
Similarly, equation-of-state insensitive relations directly connecting
macroscopic and microscopic properties of NSs can potentially provide a clean
window into the behavior of nuclear matter. In this Letter, we uncover a tight
correlation between certain macroscopic properties of NSs -- its compactness,
moment of inertia or tidal deformability -- and the ratio of central pressure
to central energy density, which can be interpreted as a mean notion of the
stiffness of nuclear matter inside a NS. We describe interesting properties of
this stiffness measure, quantify its universality, and explore its consequences
in the face of recent NS observations.

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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
2
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: supr-con
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The categories of this paper are: patt-sol
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
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The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys