Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fundamental physics and the absence of sub-millisecond pulsars   Observations of the spin distribution of rapidly rotating neutron stars show
evidence for a lack of stars spinning at frequencies larger than $f\approx 700$
Hz, well below the predictions of theoretical equations of state. This has
generally been taken as evidence of an additional spin-down torque operating in
these systems and it has been suggested that gravitational wave torques may be
operating and be linked to a potentially observable signal. In this paper we
aim to determine whether additional spin-down torques are necessary, or whether
the observed limit of $f\approx 700$ Hz could correspond to the mass-shedding
frequency for the observed systems and is simply a consequence of the,
currently unknown, state of matter at high densities. Given our ignorance with
regard to the true equation of state of matter above nuclear saturation
densities, we make minimal physical assumption and only demand causality in the
core. We then connect our causally-limited equation of state to a realistic
microphysical crustal equation of state for densities below nuclear saturation
density. This produces a limiting model that will give the lowest possible
maximum frequency, which we compare to observational constraints on neutron
star masses and frequencies. We also compare our findings with the constraints
on the tidal deformability obtained in the observations of the GW170817 event.
We find that the lack of pulsars spinning faster than $f\approx 700$ Hz is not
compatible with our causal limited `minimal' equation of state, for which the
breakup frequency cannot be lower than $f_{\rm max}\approx 1200$ Hz. A low
frequency cutoff, around $f\approx 800$ Hz could only be possible if we assume
that these systems do not contain neutron stars with masses above $M\approx 2
M_\odot$. This would have to be due either to selection effects, or possibly to
a phase transition in the interior of the neutron star.

3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
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The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin