230 research outputs found
Electrovacuum Near-horizon Geometries in Four and Five Dimensions
Associated to every stationary extremal black hole is a unique near-horizon
geometry, itself a solution of the field equations. These latter spacetimes are
more tractable to analyze and most importantly, retain properties of the
original black hole which are intrinsic to the event horizon. After reviewing
general features of near-horizon geometries, such as SO(2,1) symmetry
enhancement, I report on recent work on stationary, charged extremal black hole
solutions of the Einstein-Maxwell equations with a negative cosmological
constant in four dimensions and present a classification of near-horizon
geometries of black holes on this kind. In five dimensions, charged extremal
black hole solutions to minimal (gauged) supergravity, which arises naturally
in string theory and the gauge theory/gravity correspondence, are considered. I
consider the classification of near-horizon geometries for the subset of such
black holes which are supersymmetric. Recent progress on the classification
problem in the general extremal, non-supersymmetric case is also discussed.Comment: Invited contribution to a special issue of Classical and Quantum
Gravity on the 19th International Conference on General Relativity and
Gravitation, Mexico City, July 5-9, 201
Constructing near-horizon geometries in supergravities with hidden symmetry
We consider the classification of near-horizon geometries in a general
two-derivative theory of gravity coupled to abelian gauge fields and uncharged
scalars in four and five dimensions, with one and two commuting rotational
symmetries respectively. Assuming that the theory of gravity reduces to a 3d
non-linear sigma model (as is typically the case for ungauged supergravities),
we show that the functional form of any such near-horizon geometry may be
determined. As an example we apply this to five dimensional minimal
supergravity. We also construct an example of a five parameter near-horizon
geometry solution to this theory with S^1 X S^2 horizon topology. We discuss
its relation to the near-horizon geometries of the yet to be constructed
extremal black rings with both electric and dipole charges.Comment: Latex, 30 pages. v2: discussion in section 5 modified and improved,
other minor changes, references adde
Involvement of CytochromeP4504a in Adenosine A1 receptor mediated regulation of vascular tone
Cardiovascular diseases are one of the leading causes of morbidity and mortality worldwide. The regulation of vascular tone plays an important role in normal cardiovascular function. Adenosine, an autacoid has several physiological and pathophysiological roles, apart from the regulation of vascular tone. Adenosine receptor (AR) contracts and relaxes blood vessels through all four subtypes (A1, A2A, A2B, and A3) linked to different signaling mechanisms. Deciphering complex tissue responses remains difficult because relationships of individual receptor subtypes and various end-effectors (e.g., ion channels) are yet to be identified. Apart from adenosine, 20-HETE, a cytochrome P4504a (Cyp4a) metabolite of arachidonic acid (AA) is a potent vasoconstrictor.;We hypothesized that A1AR induced contraction of the smooth muscle involves Cyp4a, with Protein Kinase C (PKC)-alpha, extracellular regulated kinase (ERK) 1/2 contributing to the downstream signaling events. Another key question we addressed were the ion channel(s) contributing to smooth muscle contraction. Experiments included isometric tension recordings of aortic contraction and western blots. In addition, patch clamp experiments were done with freshly isolated smooth muscle cells from wild type (WT) and A1 knockout (A1KO) mice aortae. We found that inhibition of Cyp4a led to lesser contraction in the adenosine agonists\u27 mediated responses. 20-HETE induced contraction in both WT and A1KO, but this response was lower in A1KO. Inhibition of PKC-alpha and ERK1/2 attenuated the 20-HETE-induced contraction in both WT and A1KO. These findings suggest that A1AR couples with 20-HETE and negatively modulates vascular tone through PKC-alpha and ERK1/2. Furthermore, electrophysiological experiments revealed that non-selective adenosine agonist increased the BK current in A1KO as compared to the WT. This suggests A1 receptors have a negative regulatory effect on BK current. On the other hand, A1 selective agonist decreased the BK current in WT, with no effect on A1KO. PKC-alpha inhibitor abolished the effect of the A 1 selective agonist on BK current. These findings suggest that A 1AR regulates contraction of the aortic smooth muscle through inhibition of BK channels in a PKC-alpha dependent manner. From these data, we conclude that A1AR negatively couples with 20-HETE and by inhibiting BK channels mediates smooth muscle contraction via PKC-alpha
Uniqueness of near-horizon geometries of rotating extremal AdS(4) black holes
We consider stationary extremal black hole solutions of the Einstein-Maxwell
equations with a negative cosmological constant in four dimensions. We
determine all non-static axisymmetric near-horizon geometries (with
non-toroidal horizon topology) and all static near-horizon geometries for black
holes of this kind. This allows us to deduce that the most general near-horizon
geometry of an asymptotically globally AdS(4) rotating extremal black hole, is
the near-horizon limit of extremal Kerr-Newman-AdS(4). We also identify the
subset of near-horizon geometries which are supersymmetric. Finally, we show
which physical quantities of extremal black holes may be computed from the
near-horizon limit alone, and point out a simple formula for the entropy of the
known supersymmetric AdS(4) black hole. Analogous results are presented in the
case of vanishing cosmological constant.Comment: 18 pages, Latex. v2: footnote added on pg. 12. v3: assumption of
non-toroidal horizon topology made explicit, minor clarification
All Vacuum Near-Horizon Geometries in -dimensions with Commuting Rotational Symmetries
We explicitly construct all stationary, non-static, extremal near horizon
geometries in dimensions that satisfy the vacuum Einstein equations, and
that have commuting rotational symmetries. Our work generalizes
[arXiv:0806.2051] by Kunduri and Lucietti, where such a classification had been
given in . But our method is different from theirs and relies on a
matrix formulation of the Einstein equations. Unlike their method, this matrix
formulation works for any dimension. The metrics that we find come in three
families, with horizon topology , or ,
or quotients thereof. Our metrics depend on two discrete parameters specifying
the topology type, as well as continuous parameters. Not all of
our metrics in seem to arise as the near horizon limits of known
black hole solutions.Comment: 22 pages, Latex, no figures, title changed, references added,
discussion of the parameters specifying solutions corrected, amended to match
published versio
New thermodynamic identities for five-dimensional black holes
We derive new identities for the thermodynamic variables of five-dimensional,
asymptotically flat, stationary and biaxisymmetric vacuum black holes. These
identities depend on the topology of the solution and include contributions
arising from certain topological charges. The proof employs the harmonic map
formulation of the vacuum Einstein equations for solutions with these
symmetries.Comment: 5 pages. v2: minor edit
Toric Kahler metrics and AdS_5 in ring-like co-ordinates
Stationary, supersymmetric supergravity solutions in five dimensions have
Kahler metrics on the four-manifold orthogonal to the orbits of a time-like
Killing vector. We show that an explicit class of toric Kahler metrics provide
a unified framework in which to describe both the asymptotically flat and
asymptotically AdS solutions. The Darboux co-ordinates used for the local
description turn out to be ''ring-like.'' We conclude with an Ansatz for
studying the existence of supersymmetric black rings in AdS.Comment: A new appendix derives the explicit co-ordinate transformation
between the ``ring-like'' co-ordinates and the polar co-ordinates of global
AdS. Also, references adde
Do supersymmetric anti-de Sitter black rings exist?
We determine the most general near-horizon geometry of a supersymmetric,
asymptotically anti-de Sitter, black hole solution of five-dimensional minimal
gauged supergravity that admits two rotational symmetries. The near-horizon
geometry is that of the supersymmetric, topologically spherical, black hole
solution of Chong et al. This proves that regular supersymmetric anti-de Sitter
black rings with two rotational symmetries do not exist in minimal
supergravity. However, we do find a solution corresponding to the near-horizon
geometry of a supersymmetric black ring held in equilibrium by a conical
singularity, which suggests that nonsupersymmetric anti-de Sitter black rings
may exist but cannot be "balanced" in the supersymmetric limit.Comment: Latex, 18 pages, 1 figure. v2: minor change
CFT Duals for Extreme Black Holes
It is argued that the general four-dimensional extremal Kerr-Newman-AdS-dS
black hole is holographically dual to a (chiral half of a) two-dimensional CFT,
generalizing an argument given recently for the special case of extremal Kerr.
Specifically, the asymptotic symmetries of the near-horizon region of the
general extremal black hole are shown to be generated by a Virasoro algebra.
Semiclassical formulae are derived for the central charge and temperature of
the dual CFT as functions of the cosmological constant, Newton's constant and
the black hole charges and spin. We then show, assuming the Cardy formula, that
the microscopic entropy of the dual CFT precisely reproduces the macroscopic
Bekenstein-Hawking area law. This CFT description becomes singular in the
extreme Reissner-Nordstrom limit where the black hole has no spin. At this
point a second dual CFT description is proposed in which the global part of the
U(1) gauge symmetry is promoted to a Virasoro algebra. This second description
is also found to reproduce the area law. Various further generalizations
including higher dimensions are discussed.Comment: 18 pages; v2 minor change
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