9,078 research outputs found
Many accelerating black holes
We show how the Weyl formalism allows metrics to be written down which
correspond to arbitrary numbers of collinear accelerating neutral black holes
in 3+1 dimensions. The black holes have arbitrary masses and different
accelerations and share a common acceleration horizon. In the general case, the
black holes are joined by cosmic strings or struts that provide the necessary
forces that, together with the inter black hole gravitational attractions,
produce the acceleration. In the cases of two and three black holes, the
parameters may be chosen so that the outermost black hole is pulled along by a
cosmic string and the inner black holes follow behind accelerated purely by
gravitational forces. We conjecture that similar solutions exist for any number
of black holes.Comment: 12 pages, LaTe
Multi-black hole solutions in five dimensions
Using a recently developed generalized Weyl formalism, we construct an
asymptotically flat, static vacuum Einstein solution that describes a
superposition of multiple five-dimensional Schwarzschild black holes. The
spacetime exhibits a U(1)\times U(1) rotational symmetry. It is argued that for
certain choices of parameters, the black holes are collinear and so may be
regarded as a five-dimensional generalization of the Israel-Khan solution. The
black holes are kept in equilibrium by membrane-like conical singularities
along the two rotational axes; however, they still distort one another by their
mutual gravitational attraction. We also generalize this solution to one
describing multiple charged black holes, with fixed mass-to-charge ratio, in
Einstein-Maxwell-dilaton theory.Comment: 23 pages, 6 figure
General Concentric Black Rings
Supersymmetric black ring solutions of five dimensional supergravity coupled
to an arbitrary number of vector multiplets are constructed. The solutions are
asymptotically flat and describe configurations of concentric black rings which
have regular horizons with topology and no closed time-like
curves at the horizons.Comment: 8 pages, minor alterations, typos corrected. Version to be published
in PR
Dynamic and Thermodynamic Stability and Negative Modes in Schwarzschild-Anti-de Sitter
The thermodynamic properties of Schwarzschild-anti-de Sitter black holes
confined within finite isothermal cavities are examined. In contrast to the
Schwarzschild case, the infinite cavity limit may be taken which, if suitably
stated, remains double valued. This allows the correspondence between
non-existence of negative modes for classical solutions and local thermodynamic
stability of the equilibrium configuration of such solutions to be shown in a
well defined manner. This is not possible in the asymptotically flat case.
Furthermore, the non-existence of negative modes for the larger black hole
solution in Schwarzschild-anti-de Sitter provides strong evidence in favour of
the recent positive energy conjecture by Horowitz and Myers.Comment: 21 pages, 5 figures, LaTe
Effects of Family, Friends, and Relative Prices on Fruit and Vegetable Consumption by African American Youths
Facilitating healthy eating among young people, particularly among minorities who are at high risk for gaining excess weight, is at the forefront of current policy discussions and food program reviews. We investigate the effects of social interactions and relative prices on fruit and vegetable consumption by African American youths using rich behavioral data from the Family and Community Health Study and area-specific food prices. We find the presence of endogenous effects between a youth and parent, but not between a youth and friend. Lower relative prices of fruits and vegetables tend to increase intakes. Results suggest that health interventions targeting a family member may be an effective way to increase fruit and vegetable intake by African Americans as a result of spillover consumption effects between the youths and parents.social interactions, healthy food choices, fruit and vegetable consumption, African American youth, Agricultural and Food Policy, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Health Economics and Policy, Institutional and Behavioral Economics, I12, J15, C35,
Rotating Black Holes in Higher Dimensions with a Cosmological Constant
We present the metric for a rotating black hole with a cosmological constant
and with arbitrary angular momenta in all higher dimensions. The metric is
given in both Kerr-Schild and Boyer-Lindquist form. In the Euclidean-signature
case, we also obtain smooth compact Einstein spaces on associated S^{D-2}
bundles over S^2, infinitely many for each odd D\ge 5. Applications to string
theory and M-theory are indicated.Comment: 8 pages, Latex. Short version, with more compact notation, of
hep-th/0404008. To appear in Phys. Rev. Let
Bohm and Einstein-Sasaki Metrics, Black Holes and Cosmological Event Horizons
We study physical applications of the Bohm metrics, which are infinite
sequences of inhomogeneous Einstein metrics on spheres and products of spheres
of dimension 5 <= d <= 9. We prove that all the Bohm metrics on S^3 x S^2 and
S^3 x S^3 have negative eigenvalue modes of the Lichnerowicz operator and by
numerical methods we establish that Bohm metrics on S^5 have negative
eigenvalues too. We argue that all the Bohm metrics will have negative modes.
These results imply that higher-dimensional black-hole spacetimes where the
Bohm metric replaces the usual round sphere metric are classically unstable. We
also show that the stability criterion for Freund-Rubin solutions is the same
as for black-hole stability, and hence such solutions using Bohm metrics will
also be unstable. We consider possible endpoints of the instabilities, and show
that all Einstein-Sasaki manifolds give stable solutions. We show how Wick
rotation of Bohm metrics gives spacetimes that provide counterexamples to a
strict form of the Cosmic Baldness conjecture, but they are still consistent
with the intuition behind the cosmic No-Hair conjectures. We show how the
Lorentzian metrics may be created ``from nothing'' in a no-boundary setting. We
argue that Lorentzian Bohm metrics are unstable to decay to de Sitter
spacetime. We also argue that noncompact versions of the Bohm metrics have
infinitely many negative Lichernowicz modes, and we conjecture a general
relation between Lichnerowicz eigenvalues and non-uniqueness of the Dirichlet
problem for Einstein's equations.Comment: 53 pages, 11 figure
Analytical results for string propagation near a Kaluza-Klein black hole
This brief report presents analytical solutions to the equations of motion of
a null string. The background spacetime is a magnetically charged Kaluza-Klein
black hole. The string coordinates are expanded with the world-sheet velocity
of light as an expansion parameter. It is shown that the zeroth order solutions
can be expressed in terms of elementary functions in an appropriate large
distance approximation. In addition, a class of exact solutions corresponding
to the Pollard-Gross-Perry-Sorkin monopole case is also obtained.Comment: Revtex, 9 pages including two postscript figures, More detailed
discussion and new references adde
Nonsupersymmetric multibrane solutions
Gravity coupled to an arbitrary number of antisymmetric tensors and scalar
fields in arbitrary space-time dimensions is studied in a context of general,
static, spherically symmetric solutions with many orthogonally intersecting
branes. Neither supersymmetry nor harmonic gauge is assumed. It is shown that
the system reduces to a Toda-like system after an adequate redefinition of
transverse radial coordinate . Duality in the set of solutions
is observed
A Note on the Instability of Lorentzian Taub-NUT-Space
I show that there are no SU(2)-invariant (time-dependent) tensorial
perturbations of Lorentzian Taub-NUT space. It follows that the spacetime is
unstable at the linear level against generic perturbations. I speculate that
this fact is responsible for so far unsuccessful attempts to define a sensible
thermodynamics for NUT-charged spacetimes.Comment: 13 pages, no figure
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