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678
The large N limit of superconformal field theories and supergravity
, 1998
"... We show that the large N limit of certain conformal field theories in various dimensions include in their Hilbert space a sector describing supergravity on the product of AntideSitter spacetimes, spheres and other compact manifolds. This is shown by taking some branes in the full M/string theory and ..."
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Cited by 3583 (21 self)
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We show that the large N limit of certain conformal field theories in various dimensions include in their Hilbert space a sector describing supergravity on the product of AntideSitter spacetimes, spheres and other compact manifolds. This is shown by taking some branes in the full M/string theory and then taking a low energy limit where the field theory on the brane decouples from the bulk. We observe that, in this limit, we can still trust the near horizon geometry for large N. The enhanced supersymmetries of the near horizon geometry correspond to the extra supersymmetry generators present in the superconformal group (as opposed to just the superPoincare group). The ’t Hooft limit of 3+1 N = 4 superYangMills at the conformal point is shown to contain strings: they are IIB strings. We conjecture that compactifications of M/string theory on various AntideSitter spacetimes is dual to various conformal field theories. This leads to a new proposal for a definition of Mtheory which could be extended to include five or four noncompact dimensions. 1
Quasilocal energymomentum and angular momentum in General Relativity: A review article
 Living Rev. Rel
"... in relativity ..."
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From big bang to big crunch and beyond
 JHEP
"... We study a quotient Conformal Field Theory, which describes a 3 + 1 dimensional cosmological spacetime. Part of this spacetime is the NappiWitten (NW) universe, which starts at a “big bang ” singularity, expands and then contracts to a “big crunch ” singularity at a finite time. The gauged WZW mode ..."
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Cited by 55 (10 self)
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We study a quotient Conformal Field Theory, which describes a 3 + 1 dimensional cosmological spacetime. Part of this spacetime is the NappiWitten (NW) universe, which starts at a “big bang ” singularity, expands and then contracts to a “big crunch ” singularity at a finite time. The gauged WZW model contains a number of copies of the NW spacetime, with each copy connected to the preceeding one and to the next one at the respective big bang/big crunch singularities. The sequence of NW spacetimes is further connected at the singularities to a series of noncompact static regions with closed timelike curves. These regions contain boundaries, on which the observables of the theory live. This suggests a holographic interpretation of the physics. 4/02
general relativity allow an observer to view an eternity in a finite time
 Foundations of Physics Letters
, 1992
"... I investigate whether there are general relativistic spacetimes that allow an observer g to collect in a finite time all the data from the worldline of another observer ~, where the proper length of ~'s worldline is infinite. The existence of these spacetimes has a bearing on certain problems i ..."
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Cited by 49 (4 self)
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I investigate whether there are general relativistic spacetimes that allow an observer g to collect in a finite time all the data from the worldline of another observer ~, where the proper length of ~'s worldline is infinite. The existence of these spacetimes has a bearing on certain problems in computation theory. A theorem shows that most standard spacetimes cannot accommodate this scenario. There are however spacetimes which can: antide Sitter spacetime is one example. Key words: general relativity, eternity, antide Sitter, Pitowsky. 1.
Holographic protection of chronology in universes of the Goedel type,” Phys
 Rev. D
"... We analyze the structure of supersymmetric Gödellike cosmological solutions of string theory. Just as the original fourdimensional Gödel universe, these solutions represent rotating, topologically trivial cosmologies with a homogeneous metric and closed timelike curves. First we focus on “phenomen ..."
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Cited by 34 (0 self)
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We analyze the structure of supersymmetric Gödellike cosmological solutions of string theory. Just as the original fourdimensional Gödel universe, these solutions represent rotating, topologically trivial cosmologies with a homogeneous metric and closed timelike curves. First we focus on “phenomenological ” aspects of holography, and identify the preferred holographic screens associated with inertial comoving observers in Gödel universes. We find that holography can serve as a chronology protection agency: The closed timelike curves are either hidden behind the holographic screen, or broken by it into causal pieces. In fact, holography in Gödel universes has many features in common with de Sitter space, suggesting that Gödel universes could represent a supersymmetric laboratory for addressing the conceptual puzzles of de Sitter holography. Then we initiate the investigation of “microscopic ” aspects of holography of Gödel universes in string theory. We show that Gödel universes are Tdual to ppwaves, and use this fact to generate new Gödellike solutions of string and Mtheory by Tdualizing known supersymmetric ppwave solutions. December
Thermodynamics of (3+1)dimensional black holes with toroidal or higher genus black horizons, Phys. Rev. D56
, 1997
"... grqc/9705012 ..."
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Global extensions of spacetimes describing asymptotic final states of black holes Class
 Quantum Grav. 13 539 (Preprint grqc/9507055
, 1996
"... We consider a globally hyperbolic, stationary spacetime containing a black hole but no white hole. We assume, further, that the event horizon, N, of the black hole is a Killing horizon with compact crosssections. We prove that if surface gravity is nonzero constant throughout the horizon one can g ..."
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Cited by 31 (5 self)
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We consider a globally hyperbolic, stationary spacetime containing a black hole but no white hole. We assume, further, that the event horizon, N, of the black hole is a Killing horizon with compact crosssections. We prove that if surface gravity is nonzero constant throughout the horizon one can globally extend such a spacetime so that the image of N is a proper subset of a regular bifurcate Killing horizon in the enlarged spacetime. The necessary and sufficient conditions are given for the extendibility of matter fields to the enlarged spacetime. These conditions are automatically satisfied if the spacetime is static (and, hence “t”reflection symmetric) or stationaryaxisymmetric with “t − φ ” reflection isometry and the matter fields respect the reflection isometry. In addition, we prove that a necessary and sufficient condition for the constancy of the surface gravity on a Killing horizon is that the exterior derivative of the twist of the horizon Killing field vanish on the horizon. As a corollary of this, we recover a result of Carter that constancy of surface gravity holds for any black hole which is static or stationaryaxisymmetric with the “t − φ ” reflection isometry. No use of Einstein’s equation is made in obtaining any of the above results. Taken together, these results support the view that any spacetime representing the asymptotic final state of a black hole formed by gravitational collapse may be assumed to possess a bifurcate Killing horizon or a Killing horizon with vanishing surface gravity. PACS number: 04.20 Cv. 1
Loop quantum cosmology
, 2006
"... Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e. the fact that the backward evolution of a classical spacetime inevitably comes to an end after a ..."
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Cited by 29 (9 self)
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Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e. the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular realization is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. Main effects are introduced into effective classical equations which allow to avoid interpretational problems of quantum theory. They give rise to new kinds of early universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function which allows to extend spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds new light on more general issues such as time.
Some uniqueness results for dynamical horizons
 Adv. Theor. Math. Phys
, 2005
"... We first show that the intrinsic, geometrical structure of a dynamical horizon is unique. A number of physically interesting constraints are then established on the location of trapped and marginally trapped surfaces in the vicinity of any dynamical horizon. These restrictions are used to prove seve ..."
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Cited by 26 (3 self)
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We first show that the intrinsic, geometrical structure of a dynamical horizon is unique. A number of physically interesting constraints are then established on the location of trapped and marginally trapped surfaces in the vicinity of any dynamical horizon. These restrictions are used to prove several uniqueness theorems for dynamical horizons. Ramifications of some of these results to numerical simulations of black hole spacetimes are discussed. Finally several expectations on the interplay between isometries and dynamical horizons are shown to be borne out. 1