Stability of topological neutron stars. (arXiv:2005.02750v1 [gr-qc])
<a href="http://arxiv.org/find/gr-qc/1/au:+Doneva_D/0/1/0/all/0/1">Daniela D. Doneva</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Yazadjiev_S/0/1/0/all/0/1">Stoytcho S. Yazadjiev</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Kokkotas_K/0/1/0/all/0/1">Kostas D. Kokkotas</a>
Tensor-multi-scalar theories (TMST) are among the most natural
generalizations of Einstein’s theory, they are mathematically self-consistent
and free from pathologies. They pass through all the known observations but
contrary to standard scalar-tensor theories, TMST offer extremely rich spectrum
of solutions and allow for large deviations from general relativity. One of the
most interesting objects in these theories are the topological neutron stars.
The main goal in the present paper is to study their radial stability since
many branches of solutions can exist even for a fixed value of the topological
charge. It turns out that only one of these branches is stable for each value
of the topological charge while all the rest are unstable. The stable branch is
exactly the one that spans from small to large neutron star masses having as
well moderate values of the radii in agreement with the observations. As
expected, it becomes unstable at the maximum of the mass. The frequencies of
the radial modes are examined and it turns out that in most cases the mode
frequencies are larger than the general relativistic ones and they increase
with the increase of the topological charge. All this shows that the
topological neutron stars are viable astrophysical objects that should be
explored further in order to determine their observational manifestations.
Tensor-multi-scalar theories (TMST) are among the most natural
generalizations of Einstein’s theory, they are mathematically self-consistent
and free from pathologies. They pass through all the known observations but
contrary to standard scalar-tensor theories, TMST offer extremely rich spectrum
of solutions and allow for large deviations from general relativity. One of the
most interesting objects in these theories are the topological neutron stars.
The main goal in the present paper is to study their radial stability since
many branches of solutions can exist even for a fixed value of the topological
charge. It turns out that only one of these branches is stable for each value
of the topological charge while all the rest are unstable. The stable branch is
exactly the one that spans from small to large neutron star masses having as
well moderate values of the radii in agreement with the observations. As
expected, it becomes unstable at the maximum of the mass. The frequencies of
the radial modes are examined and it turns out that in most cases the mode
frequencies are larger than the general relativistic ones and they increase
with the increase of the topological charge. All this shows that the
topological neutron stars are viable astrophysical objects that should be
explored further in order to determine their observational manifestations.
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