44 research outputs found
Geometric Properties of Static EMdL Horizons
We study non-degenerate and degenerate (extremal) Killing horizons of
arbitrary geometry and topology within the Einstein-Maxwell-dilaton model with
a Liouville potential (the EMdL model) in d-dimensional (d>=4) static
space-times. Using Israel's description of a static space-time, we construct
the EMdL equations and the space-time curvature invariants: the Ricci scalar,
the square of the Ricci tensor, and the Kretschmann scalar. Assuming that
space-time metric functions and the model fields are real analytic functions in
the vicinity of a space-time horizon, we study behavior of the space-time
metric and the fields near the horizon and derive relations between the
space-time curvature invariants calculated on the horizon and geometric
invariants of the horizon surface. The derived relations generalize the similar
relations known for horizons of static four and 5-dimensional vacuum and
4-dimensional electrovacuum space-times. Our analysis shows that all the
extremal horizon surfaces are Einstein spaces. We present necessary conditions
for existence of static extremal horizons within the EMdL model.Comment: 10 page
Thermodynamic of Distorted Reissner-Nordstr\"om Black Holes in Five-dimensions
In this paper, we study mechanics and thermodynamics of distorted,
five-dimensional, electrically charged (non-extremal) black holes on the
example of a static and "axisymmetric" black hole distorted by external,
electrically neutral matter. Such a black hole is represented by the derived
here solution of the Einstein-Maxwell equations which admits an
isometry group. We study the properties of
this distorted black hole.Comment: 7 pages, submitted for the proceedings of the First Karl
Schwarzschild Meeting (Frankfurt, 2013
Universal properties of distorted Kerr-Newman black holes
We discuss universal properties of axisymmetric and stationary configurations
consisting of a central black hole and surrounding matter in Einstein-Maxwell
theory. In particular, we find that certain physical equations and inequalities
(involving angular momentum, electric charge and horizon area) are not
restricted to the Kerr-Newman solution but can be generalized to the situation
where the black hole is distorted by an arbitrary axisymmetric and stationary
surrounding matter distribution.Comment: 7 page
Distorted 5-dimensional vacuum black hole
In this paper we study how the distortion generated by a static and neutral
distribution of external matter affects a 5-dimensional
Schwarzschild-Tangherlini black hole. A solution representing a particular
class of such distorted black holes admits an RxU(1)xU(1) isometry group. We
show that there exists a certain duality transformation between the black hole
horizon and a stretched singularity surfaces. The space-time near the distorted
black hole singularity has the same topology and Kasner exponents as those of a
5-dimensional Schwarzschild-Tangherlini black hole. We calculate the maximal
proper time of free fall of a test particle from the distorted black hole
horizon to its singularity and find that, depending on the distortion, it can
be less, equal to, or greater than that of a Schwarzschild-Tangherlini black
hole of the same horizon area. This implies that due to the distortion, the
singularity of a Schwarzschild-Tangherlini black hole can come close to its
horizon. A relation between the Kretschmann scalar calculated on the horizon of
a 5-dimensional static, asymmetric, distorted black hole and the trace of the
square of the Ricci tensor of the horizon surface is derived.Comment: 20 pages, 9 figure
Localization of the SFT inspired Nonlocal Linear Models and Exact Solutions
A general class of gravitational models driven by a nonlocal scalar field
with a linear or quadratic potential is considered. We study the action with an
arbitrary analytic function , which has both simple and double roots.
The way of localization of nonlocal Einstein equations is generalized on models
with linear potentials. Exact solutions in the Friedmann-Robertson-Walker and
Bianchi I metrics are presented.Comment: 20 pages, 3 figures, published in the proceedings of the VIII
International Workshop "Supersymmetries and Quantum Symmetries" (SQS'09),
Dubna, Russia, July 29 - August 3, 2009, http://theor.jinr.ru/~sqs09
Interior of a Charged Distorted Black Hole
We study interior of a charged, non-rotating distorted black hole. We
consider static and axisymmetric black holes, and focus on a special case when
an electrically charged distorted solution is obtained by the Harrison-Ernst
transformation from an uncharged one. We demonstrate that the Cauchy horizon of
such black hole remains regular, provided the distortion is regular at the
event horizon. The shape and the inner geometry of both the outer and inner
(Cauchy) horizons are studied. We demonstrate that there exists a duality
between the properties of the horizons. Proper time of a free fall of a test
particle moving in the interior of the distorted black hole along the symmetry
axis is calculated. We also study the property of the curvature in the inner
domain between the horizons. Simple relations between the 4D curvature
invariants and the Gaussian curvature of the outer and inner horizon surfaces
are found.Comment: 14 pages, 11 figures. References added, typos corrected. Some minor
changes in the tex
Percutaneous device closure for secundum-type atrial septal defect: Short and intermediate-term results
BACKGROUND: Device closure of an isolated secundum type atrial septal defect (ASD) has been used as an alternative method for open surgical closure with comparable success and lower morbidity. In this study we evaluated the procedural success and mid-term follow-up results of percutaneous closure of secundum ASD with an Amplatzer�Septal Occluder(ASO) device or a Figula ASD occluder device. METHODS: From June 2001 to January 2009, 74 consecutive patients were scheduled for percutaneous device closure in two centers in Tehran, Iran. All patients had a stretched defect diameter of 30mm or less. After using a sizing balloon to measure the stop-flow diameter, device implantation was performed under the guidance of a trans-esophageal echocardiography (TEE).The size was generally 1 - 2 mm larger than the stretched diameter. Patients were followed for an average of 11 ±4 months. RESULTS: The median stretched diameter of the defect was 20.7±4.8 mm (range: 8 - 30 mm).A total of 73 devices were used in this study. Device closure was successful in 72 (97.2) out of 74 patients. Repositioning of the device was required in one patient. Major complications(including significant residual shunt and device embolization) occurred in 3 (4) patients.There was no procedure-related mortality in our patients. Mild-to-moderate residual shunt was detectable in 10 (13.7) patients immediately following the procedure and in 5 (6.7) patients 24 hours after the procedure. None had residual flow across the device at the end of the follow-up period. CONCLUSION: Device closure of ASD has a safety profile comparable to open surgical repair and can effectively close the defect with excellent procedural and mid-term results
Lifshitz black holes in Brans-Dicke theory
We present an exact asymptotically Lifshitz black hole solution in
Brans-Dicke theory of gravity in arbitrary dimensions in presence of
a power-law potential. In this solution, the dynamical exponent is
determined in terms of the Brans-Dicke parameter and . Asymptotic
Lifshitz condition at infinity requires , which corresponds to
. On the other hand, the no-ghost condition
for the scalar field in the Einstein frame requires . We
compute the Hawking temperature of the black hole solution and discuss the
problems encountered and the proposals in defining its thermodynamic
properties. A generalized solution charged under the Maxwell field is also
presented.Comment: 32 pages, no figure. v2: revised version. Section 3.1 and Appendix B
improved. The argument in Appendix A clarified. v3: References added. v4:
analysis on the black hole thermodynamical properties corrected. Final
version to appear in JHE
Hawking Radiation from Higher-Dimensional Black Holes
We review the quantum field theory description of Hawking radiation from evaporating black holes and summarize what is known about Hawking radiation from black holes in more than four space-time dimensions. In the context of the Large Extra Dimensions scenario, we present the theoretical formalism for all types of emitted fields and a selection of results on the radiation spectra. A detailed analysis of the Hawking fluxes in this case is essential for modelling the evaporation of higher-dimensional black holes at the LHC, whose creation is predicted by low-energy models of quantum gravity. We discuss the status of the quest for black-hole solutions in the context of the Randall-Sundrum brane-world model and, in the absence of an exact metric, we review what is known about Hawking radiation from such black holes