488 research outputs found
Distorted Black Holes with Charge
We present new solutions to the Einstein-Maxwell equations representing a
class of charged distorted black holes. These solutions are static-axisymmetric
and are generalizations of the distorted black hole solutions studied by Geroch
and Hartle. Physically, they represent a charged black hole distorted by
external matter fields. We discuss the zeroth and first law for these black
holes. The first law is proved in two different forms, one motivated by the
isolated horizon framework and the other using normalizations at infinity.Comment: 18 pages, LaTe
Respiratory hospital admission risk near large composting facilities
AbstractBackgroundLarge-scale composting can release bioaerosols in elevated quantities, but there are few studies of health effects on nearby communities.MethodsA cross-sectional ecological small area design was used to examine risk of respiratory hospital admissions within 2500m of all 148 English large-scale composting facilities in 2008–10. Statistical analyses used a random intercept Poisson regression model at Census Output Area (COA) level (mean population 310). Models were adjusted for age, sex, deprivation and tobacco sales.ResultsAnalysing 34,963 respiratory hospital admissions in 4656 COAs within 250–2500m of a site, there were no significant trends using pre-defined distance bands of >250–750m, >750–1500m and >1500–2500m. Using a continuous measure of distance, there was a small non-statistically significant (p=0.054) association with total respiratory admissions corresponding to a 1.5% (95% CI: 0.0–2.9%) decrease in risk if moving from 251m to 501m. There were no significant associations for subgroups of respiratory infections, asthma or chronic obstructive pulmonary disease.ConclusionThis national study does not provide evidence for increased risks of respiratory hospital admissions in those living beyond 250m of an outdoor composting area perimeter. Further work using better measures of exposure and exploring associations with symptoms and disease prevalence, especially in vulnerable groups, is recommended to support regulatory approaches
Proof of a generalized Geroch conjecture for the hyperbolic Ernst equation
We enunciate and prove here a generalization of Geroch's famous conjecture
concerning analytic solutions of the elliptic Ernst equation. Our
generalization is stated for solutions of the hyperbolic Ernst equation that
are not necessarily analytic, although it can be formulated also for solutions
of the elliptic Ernst equation that are nowhere axis-accessible.Comment: 75 pages (plus optional table of contents). Sign errors in elliptic
case equations (1A.13), (1A.15) and (1A.25) are corrected. Not relevant to
proof contained in pape
A Radiation Scalar for Numerical Relativity
This letter describes a scalar curvature invariant for general relativity
with a certain, distinctive feature. While many such invariants exist, this one
vanishes in regions of space-time which can be said unambiguously to contain no
gravitational radiation. In more general regions which incontrovertibly support
non-trivial radiation fields, it can be used to extract local,
coordinate-independent information partially characterizing that radiation.
While a clear, physical interpretation is possible only in such radiation
zones, a simple algorithm can be given to extend the definition smoothly to
generic regions of space-time.Comment: 4 pages, 1 EPS figur
Static axisymmetric spacetimes with non-generic world-line SUSY
The conditions for the existence of Killing-Yano tensors, which are closely
related to the appearance of non-generic world-line SUSY, are presented for
static axisymmetric spacetimes. Imposing the vacuum Einstein equation, the set
of solutions admitting Killing-Yano tensors is considered. In particular, it is
shown that static, axisymmetric and asymptotically flat vacuum solutions
admitting Killing-Yano tensors are only the Schwarzschild solution.Comment: 10 pages (RevTeX), TIT/HEP-253/COSMO-4
Uniformly accelerating black holes in a de Sitter universe
A class of exact solutions of Einstein's equations is analysed which
describes uniformly accelerating charged black holes in an asymptotically de
Sitter universe. This is a generalisation of the C-metric which includes a
cosmological constant. The physical interpretation of the solutions is
facilitated by the introduction of a new coordinate system for de Sitter space
which is adapted to accelerating observers in this background. The solutions
considered reduce to this form of the de Sitter metric when the mass and charge
of the black holes vanish.Comment: 6 pages REVTeX, 3 figures, to appear in Phys. Rev. D. Figure 2
correcte
Pair creation of black holes joined by cosmic strings
We argue that production of charged black hole pairs joined by a cosmic
string in the presence of a magnetic field can be analyzed using the Ernst
metric. The effect of the cosmic string is to pull the black holes towards each
other, opposing to the background field. An estimation of the production rate
using the Euclidean action shows that the process is suppressed as compared to
the formation of black holes without strings.Comment: 7 pages, LaTeX. Minor typos corrected
Higher Spin Field Equation in a Virtual Black Hole Metric
In a quantum theory of gravity, fluctuations about the vacuum may be
considered as Planck scale virtual black holes appearing and annihilating in
pairs. Incident fields scattering from such fluctuations would lose quantum
coherence.
In a recent paper (hep-th/9705147), Hawking and Ross obtained an estimate for
the magnitude of this loss in the case of a scalar field. Their calculation
exploited the separability of the conformally invariant scalar wave equation in
the electrovac C metric background, which is justified as a sufficiently good
description of a virtual black hole pair in the limit considered.
In anticipation of extending this result, the Teukolsky equations for
incident fields of higher spin are separated on the vacuum C metric background
and solved in the same limit. With the exception of spin 2 fields, these
equations are shown in addition to be valid on the electrovac C metric
background. The angular solutions are found to reduce to the spin- weighted
spherical harmonics, and the radial solutions are found to approach
hypergeometrics close to the horizons.
By defining appropriate scattering boundary conditions, these solutions are
then used to estimate the transmission and reflection coefficients for an
incident field of spin s. The transmission coefficient is required in order to
estimate the loss of quantum coherence of an incident field through scattering
off virtual black holes.Comment: 23 pages, 3 figures, LaTeX, minor typo correcte
Einstein's equations and the chiral model
The vacuum Einstein equations for spacetimes with two commuting spacelike
Killing field symmetries are studied using the Ashtekar variables. The case of
compact spacelike hypersurfaces which are three-tori is considered, and the
determinant of the Killing two-torus metric is chosen as the time gauge. The
Hamiltonian evolution equations in this gauge may be rewritten as those of a
modified SL(2) principal chiral model with a time dependent `coupling
constant', or equivalently, with time dependent SL(2) structure constants. The
evolution equations have a generalized zero-curvature formulation. Using this
form, the explicit time dependence of an infinite number of
spatial-diffeomorphism invariant phase space functionals is extracted, and it
is shown that these are observables in the sense that they Poisson commute with
the reduced Hamiltonian. An infinite set of observables that have SL(2) indices
are also found. This determination of the explicit time dependence of an
infinite set of spatial-diffeomorphism invariant observables amounts to the
solutions of the Hamiltonian Einstein equations for these observables.Comment: 22 pages, RevTeX, to appear in Phys. Rev.
How can exact and approximate solutions of Einstein's field equations be compared?
The problem of comparison of the stationary axisymmetric vacuum solutions
obtained within the framework of exact and approximate approaches for the
description of the same general relativistic systems is considered. We suggest
two ways of carrying out such comparison: (i) through the calculation of the
Ernst complex potential associated with the approximate solution whose form on
the symmetry axis is subsequently used for the identification of the exact
solution possessing the same multipole structure, and (ii) the generation of
approximate solutions from exact ones by expanding the latter in series of
powers of a small parameter. The central result of our paper is the derivation
of the correct approximate analogues of the double-Kerr solution possessing the
physically meaningful equilibrium configurations. We also show that the
interpretation of an approximate solution originally attributed to it on the
basis of some general physical suppositions may not coincide with its true
nature established with the aid of a more accurate technique.Comment: 32 pages, 5 figure
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