8 research outputs found
Testing Einstein-dilaton-Gauss-Bonnet gravity with the reflection spectrum of accreting black holes
Einstein-dilaton-Gauss-Bonnet gravity is a theoretically well-motivated alternative theory of gravity emerging as a low-energy four-dimensional model from heterotic string theory. Its rotating black hole solutions are known numerically and can have macroscopic deviations from the Kerr black holes of Einstein's gravity. Einstein-dilaton-Gauss-Bonnet gravity can thus be tested with observations of astrophysical black holes. In the present paper, we simulate observations of the reflection spectrum of thin accretion disks with present and future x-ray facilities to understand whether x-ray reflection spectroscopy can distinguish the black holes in Einstein-dilaton-Gauss-Bonnet gravity from those in Einstein's gravity. We find that this is definitively out of reach for present x-ray missions, but it may be achieved with the next generation of facilities
New generalized nonspherical black hole solutions
We present numerical evidence for the existence of several types of static
black hole solutions with a nonspherical event horizon topology in
spacetime dimensions. These asymptotically flat configurations are found for a
specific metric ansatz and can be viewed as higher dimensional counterparts of
the static black rings, dirings and black Saturn. Similar to that case,
they are supported against collapse by conical singularities. The issue of
rotating generalizations of these solutions is also considered.Comment: 47 pages, 11 figures, some comments adde
Rotating black holes with equal-magnitude angular momenta in d=5 Einstein-Gauss-Bonnet theory
We construct rotating black hole solutions in Einstein-Gauss-Bonnet theory in
five spacetime dimensions. These black holes are asymptotically flat, and
possess a regular horizon of spherical topology and two equal-magnitude angular
momenta associated with two distinct planes of rotation. The action and global
charges of the solutions are obtained by using the quasilocal formalism with
boundary counterterms generalized for the case of Einstein-Gauss-Bonnet theory.
We discuss the general properties of these black holes and study their
dependence on the Gauss-Bonnet coupling constant . We argue that most
of the properties of the configurations are not affected by the higher
derivative terms. For fixed the set of black hole solutions terminates
at an extremal black hole with a regular horizon, where the Hawking temperature
vanishes and the angular momenta attain their extremal values. The domain of
existence of regular black hole solutions is studied. The near horizon geometry
of the extremal solutions is determined by employing the entropy function
formalism.Comment: 25 pages, 7 figure
Charged-rotating black holes and black strings in higher dimensional Einstein-Maxwell theory with a positive cosmological constant
We present arguments for the existence of charged, rotating black holes in
dimensions, with with a positive cosmological constant.
These solutions posses both, a regular horizon and a cosmological horizon of
spherical topology and have equal-magnitude angular momenta. They approach
asymptotically the de Sitter spacetime background. The counterpart equations
for are investigated, by assuming that the fields are independant of
the extra dimension , leading to black strings solutions. These solutions
are regular at the event horizon. The asymptotic form of the metric is not the
de Sitter form and exhibit a naked singularity at finite proper distance.Comment: 21 pages, 9 figure
Non-uniform Black Strings with Schwarzschild-(Anti-)de Sitter Foliation
We present some exact non-uniform black string solutions of 5-dimensional
pure Einstein gravity as well as Einstein-Maxwell-dilaton theory at arbitrary
dilaton coupling. The solutions share the common property that their
4-dimensional slices are Schwarzchild-(anti-)de Sitter spacetimes. The pure
gravity solution is also generalized to spacetimes of dimensions higher than 5
to get non-uniform black branes.Comment: LaTeX 14 pages, 3 eps figures. V2: version appeared in CQ
Existence of spinning solitons in gauge field theory
We study the existence of classical soliton solutions with intrinsic angular
momentum in Yang-Mills-Higgs theory with a compact gauge group in
(3+1)-dimensional Minkowski space. We show that for \textit{symmetric} gauge
fields the Noether charges corresponding to \textit{rigid} spatial symmetries,
as the angular momentum, can be expressed in terms of \textit{surface}
integrals. Using this result, we demonstrate in the case of
the nonexistence of stationary and axially symmetric spinning excitations for
all known topological solitons in the one-soliton sector, that is, for 't
Hooft--Polyakov monopoles, Julia-Zee dyons, sphalerons, and also vortices.Comment: 21 pages, to appear in Phys.Rev.
Generalized Weyl solutions in d=5 Einstein-Gauss-Bonnet theory: the static black ring
We argue that the Weyl coordinates and the rod-structure employed to
construct static axisymmetric solutions in higher dimensional Einstein gravity
can be generalized to the Einstein-Gauss-Bonnet theory. As a concrete
application of the general formalism, we present numerical evidence for the
existence of static black ring solutions in Einstein-Gauss-Bonnet theory in
five spacetime dimensions. They approach asymptotically the Minkowski
background and are supported against collapse by a conical singularity in the
form of a disk. An interesting feature of these solutions is that the
Gauss-Bonnet term reduces the conical excess of the static black rings.
Analogous to the Einstein-Gauss-Bonnet black strings, for a given mass the
static black rings exist up to a maximal value of the Gauss-Bonnet coupling
constant . Moreover, in the limit of large ring radius, the suitably
rescaled black ring maximal value of and the black string maximal
value of agree.Comment: 43 pages, 14 figure
Dynamical Boson Stars
The idea of stable, localized bundles of energy has strong appeal as a model
for particles. In the 1950s John Wheeler envisioned such bundles as smooth
configurations of electromagnetic energy that he called {\em geons}, but none
were found. Instead, particle-like solutions were found in the late 1960s with
the addition of a scalar field, and these were given the name {\em boson
stars}. Since then, boson stars find use in a wide variety of models as sources
of dark matter, as black hole mimickers, in simple models of binary systems,
and as a tool in finding black holes in higher dimensions with only a single
killing vector. We discuss important varieties of boson stars, their dynamic
properties, and some of their uses, concentrating on recent efforts.Comment: 79 pages, 25 figures, invited review for Living Reviews in
Relativity; major revision in 201