Speed of sound constraints on rapidly-rotating neutron stars. (arXiv:1910.05767v1 [nucl-th])
<a href="http://arxiv.org/find/nucl-th/1/au:+Margaritis_C/0/1/0/all/0/1">Ch. Margaritis</a>, <a href="http://arxiv.org/find/nucl-th/1/au:+Koliogiannis_P/0/1/0/all/0/1">P. S. Koliogiannis</a>, <a href="http://arxiv.org/find/nucl-th/1/au:+Moustakidis_C/0/1/0/all/0/1">Ch. C. Moustakidis</a>

The observation of rapidly-rotating neutron stars (in comparison with
non-rotating ones) may provide even richer information on the behavior of the
properties of nuclear matter at high densities. In the present work we provide
a theoretical treatment concerning the effects of the upper bound of the speed
of sound in dense matter on the bulk properties of rapidly-rotating (at Kepler
limit) neutron stars. In particular, we consider two upper bounds for the speed
of sound, $upsilon_{s} = c$ and $upsilon_{s} = c/sqrt{3}$, and the one
provided by the kinetic theory. We investigate to what extent the possible
predicted (from various theories and conjectures) upper bounds on the speed of
sound constraints the ones of various key quantities, including the maximum
mass and the corresponding radius, Keplerian frequency, Kerr parameter and
moment of inertia. We mainly focus on the lower proposed limit,
$upsilon_{s}=c/sqrt{3}$, and we explore in which mass region a rotating
neutron star collapses to a black hole. In any case, useful relations of the
mentioned bulk properties with the transition density, are derived and compared
with the case of non-rotating neutron stars. We concluded that the limit
$upsilon_{s}=c/sqrt{3}$, leads to dramatic decrease on the values of the
maximum mass, Kerr parameter and moment of inertia preventing a neutron star to
reach values which derive from other consideration or constraints.

The observation of rapidly-rotating neutron stars (in comparison with
non-rotating ones) may provide even richer information on the behavior of the
properties of nuclear matter at high densities. In the present work we provide
a theoretical treatment concerning the effects of the upper bound of the speed
of sound in dense matter on the bulk properties of rapidly-rotating (at Kepler
limit) neutron stars. In particular, we consider two upper bounds for the speed
of sound, $upsilon_{s} = c$ and $upsilon_{s} = c/sqrt{3}$, and the one
provided by the kinetic theory. We investigate to what extent the possible
predicted (from various theories and conjectures) upper bounds on the speed of
sound constraints the ones of various key quantities, including the maximum
mass and the corresponding radius, Keplerian frequency, Kerr parameter and
moment of inertia. We mainly focus on the lower proposed limit,
$upsilon_{s}=c/sqrt{3}$, and we explore in which mass region a rotating
neutron star collapses to a black hole. In any case, useful relations of the
mentioned bulk properties with the transition density, are derived and compared
with the case of non-rotating neutron stars. We concluded that the limit
$upsilon_{s}=c/sqrt{3}$, leads to dramatic decrease on the values of the
maximum mass, Kerr parameter and moment of inertia preventing a neutron star to
reach values which derive from other consideration or constraints.

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