3,606 research outputs found
Chaos around the superposition of a monopole and a thick disk
We extend recent investigations on the integrability of oblique orbits of
test particles under the gravitational field corresponding to the superposition
of an infinitesimally thin disk and a monopole to the more realistic case, for
astrophysical purposes, of a thick disk. Exhaustive numerical analyses were
performed and the robustness of the recent results is confirmed. We also found
that, for smooth distributions of matter, the disk thickness can attenuate the
chaotic behavior of the bounded oblique orbits. Perturbations leading to the
breakdown of the reflection symmetry about the equatorial plane, nevertheless,
may enhance significantly the chaotic behavior, in agreement with recent
studies on oblate models.Comment: 11 pages, 4 figure
New no-scalar-hair theorem for black-holes
A new no-hair theorem is formulated which rules out a very large class of
non-minimally coupled finite scalar dressing of an asymptotically flat, static,
and spherically symmetric black-hole. The proof is very simple and based in a
covariant method for generating solutions for non-minimally coupled scalar
fields starting from the minimally coupled case. Such method generalizes the
Bekenstein method for conformal coupling and other recent ones. We also discuss
the role of the finiteness assumption for the scalar field.Comment: Revtex, 12 page
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