arXiv subjects

Dietmar Klemm

Publications and source records attributed to Dietmar Klemm.

At least 55 records · Page 3Linked to original sources

arXiv2007

Chern-Simons formulation of three-dimensional gravity with torsion and nonmetricity

We consider various models of three-dimensional gravity with torsion or nonmetricity (metric affine gravity), and show that they can be written as Chern-Simons theories with suitable gauge groups. Using the groups ISO(2,1), SL(2,C) or SL(2,R) x SL(2,R), and the fact that they admit two independent coupling constants, we obtain the Mielke-Baekler model for zero, positive or negative effective cosmological constant respectively. Choosing SO(3,2) as gauge group, one gets a generalization of conformal gravity that has zero torsion and only the trace part of the nonmetricity. This characterizes a Weyl structure. Finally, we present a new topological model of metric affine gravity in three dimensions arising from an SL(4,R) Chern-Simons theory.

hep-th↗

arXiv2007

Supersymmetric gyratons in five dimensions

We obtain the gravitational and electromagnetic field of a spinning radiation beam-pulse (a gyraton) in minimal five-dimensional gauged supergravity and show under which conditions the solution preserves part of the supersymmetry. The configurations represent generalizations of Lobatchevski waves on AdS with nonzero angular momentum, and possess a Siklos-Virasoro reparametrization invariance. We compute the holographic stress-energy tensor of the solutions and show that it transforms without anomaly under these reparametrizations. Furthermore, we present supersymmetric gyratons both in gauged and ungauged five-dimensional supergravity coupled to an arbitrary number of vector supermultiplets, which include gyratons on domain walls.

hep-th↗

arXiv2005

Chronology Protection in anti-de Sitter

We consider 1/2 BPS excitations of AdS(5)xS(5) geometries in type IIB string theory that can be mapped into free fermion configurations according to the prescription of Lin, Lunin and Maldacena (LLM). It is shown that whenever the fermionic probability density exceeds one or is negative, closed timelike curves appear in the bulk. A violation of the Pauli exclusion principle in the phase space of the fermions is thus intimately related to causality violation in the dual geometries.

hep-th↗

arXiv2004

On the Thermodynamics of Goedel Black Holes

After a brief review of Goedel-type universes in string theory, we discuss some intriguing properties of black holes immersed in such backgrounds. Among these are the upper bound on the entropy that points towards a finite-dimensional Hilbert space of a holographically dual theory, and the minimum black hole temperature that is reminiscent of the Hawking-Page transition. Furthermore, we discuss several difficulties that are encountered when one tries to formulate a consistent thermodynamics of Goedel black holes, and point out how they may be circumvented.

hep-th↗

arXiv2004

Aspects of Quantum Gravity in de Sitter Spaces

In these lectures we give a review of recent attempts to understand quantum gravity on de Sitter spaces. In particular, we discuss the holographic correspondence between de Sitter gravity and conformal field theories proposed by Hull and by Strominger, and how this may be reconciled with the finite-dimensional Hilbert space proposal by Banks and Fischler. Furthermore we review the no-go theorems that forbid an embedding of de Sitter spaces in string theory, and discuss how they can be circumvented. Finally, some curious issues concerning the thermal nature of de Sitter space are elucidated.

hep-th↗

arXiv2004

Black holes and singularities in string theory

This is a summary of a lecture I gave at the workshop on dynamics and thermodynamics of black holes and naked singularities at Politecnico Milano. It is directed to a non-expert audience and reviews several ways in which string theory accounts for black hole microstates. In particular, I give an elementary introduction to the correspondence principle by Horowitz/Polchinski, to the state counting for the three-charge black hole by Strominger and Vafa, and to the recent proposal by Mathur et al. concerning the gravity description of black hole microstates. The second part of the lecture is dedicated to naked singularities and reviews an argument by Horowitz and Myers why naked singularities are not necessarily bad. Finally, I comment on a possible resolution of singularities in Born-Infeld type gravity theories.

hep-th↗

arXiv2004

Black holes in Goedel-type universes with a cosmological constant

We discuss supersymmetric black holes embedded in a Goedel-type universe with cosmological constant in five dimensions. The spacetime is a fibration over a four-dimensional Kaehler base manifold, and generically has closed timelike curves. Asymptotically the space approaches a deformation of AdS_5, which suggests that the appearance of closed timelike curves should have an interpretation in some deformation of D=4, N=4 super-Yang-Mills theory. Finally, a Goedel-de Sitter universe is also presented and its causal structure is discussed.

hep-th↗

arXiv2003

Supersymmetric Godel-type Universe in four Dimensions

We generalize the classification of all supersymmetric solutions of pure N=2, D=4 gauged supergravity to the case when external sources are included. It is shown that the source must be an electrically charged dust. We give a particular solution to the resulting equations, that describes a Goedel-type universe preserving one quarter of the supersymmetries.

hep-th↗

arXiv2003

All Supersymmetric Solutions of N=2, D=4 Gauged Supergravity

We classify all supersymmetric solutions of minimal gauged supergravity in four dimensions. There are two classes of solutions that are distinguished by the norm of the Killing vector constructed from the Killing spinor. If the Killing vector is timelike, the solutions are determined by the geometry of a two-dimensional base-manifold. When it is lightlike, the most general BPS solution is given by an electrovac AdS travelling wave. This supersymmetric configuration was previously unknown. Generically the solutions preserve one quarter of the supersymmetry. Also in the timelike case we show that there exist new BPS solutions, which are of Petrov type I, and are thus more general than the previously known type D configurations. These geometries can be uplifted to obtain new solutions of eleven-dimensional supergravity.

hep-th↗

arXiv2003

Non(anti)commutative Superspace

We investigate the most general non(anti)commutative geometry in N=1 four-dimensional superspace, invariant under the classical (i.e., undeformed) supertranslation group. We find that a nontrivial non(anti)commutative superspace geometry compatible with supertranslations exists with non(anti)commutation parameters which may depend on the spinorial coordinates. The algebra is in general nonassociative. Imposing associativity introduces additional constraints which however allow for nontrivial commutation relations involving fermionic coordinates. We obtain explicitly the first three terms of a series expansion in the deformation parameter for a possible associative *-product. We also consider the case of N=2 euclidean superspace where the different conjugation relations among spinorial coordinates allow for a more general supergeometry.

hep-th↗

arXiv2003

Supersymmetric Domain Walls and Strings in D=5 gauged Supergravity coupled to Vector Multiplets

We present new supersymmetric domain wall and string solutions of five-dimensional N = 2 gauged supergravity coupled to an arbitrary number of vector multiplets. Using the techniques of very special geometry allows to obtain the most general domain wall preserving half of the supersymmetries. This solution, which describes a renormalization group flow in the dual field theory, is given in terms of Weierstrass elliptic functions. The magnetically charged, one quarter supersymmetric string solutions are shown to be closely related to Liouville theory. We furthermore investigate general product space compactifications, and show that topological transitions from AdS_3 x S^2 to AdS_3 x H^2 can occur when one moves in moduli space.

hep-th↗

arXiv2003

AdS_2 Supergravity and Superconformal Quantum Mechanics

We investigate the asymptotic dynamics of topological anti-de Sitter supergravity in two dimensions. Starting from the formulation as a BF theory, it is shown that the AdS_2 boundary conditions imply that the asymptotic symmetries form a super-Virasoro algebra. Using the central charge of this algebra in Cardy's formula, we exactly reproduce the thermodynamical entropy of AdS_2 black holes. Furthermore, we show that the dynamics of the dilaton and its superpartner reduces to that of superconformal transformations that leave invariant one chiral component of the stress tensor supercurrent of a two-dimensional conformal field theory. This dynamics is governed by a supersymmetric extension of the de Alfaro-Fubini-Furlan model of conformal quantum mechanics. Finally, two-dimensional de Sitter gravity is also considered, and the dS_2 entropy is computed by counting CFT states.

hep-th↗

arXiv2002

De Sitter Gravity and Liouville Theory

We show that the spectrum of conical defects in three-dimensional de Sitter space is in one-to-one correspondence with the spectrum of vertex operators in Liouville conformal field theory. The classical conformal dimensions of vertex operators are equal to the masses of the classical point particles in dS_3 that cause the conical defect. The quantum dimensions instead are shown to coincide with the mass of the Kerr-dS_3 solution computed with the Brown-York stress tensor. Therefore classical de Sitter gravity encodes the quantum properties of Liouville theory. The equality of the gravitational and the Liouville stress tensor provides a further check of this correspondence. The Seiberg bound for vertex operators translates on the bulk side into an upper mass bound for classical point particles. Bulk solutions with cosmological event horizons correspond to microscopic Liouville states, whereas those without horizons correspond to macroscopic (normalizable) states. We also comment on recent criticism by Dyson, Lindesay and Susskind, and point out that the contradictions found by these authors may be resolved if the dual CFT is not able to capture the thermal nature of de Sitter space. Indeed we find that on the CFT side, de Sitter entropy is merely Liouville momentum, and thus has no statistical interpretation in this approach.

hep-th↗

arXiv2002

The Asymptotic Dynamics of two-dimensional (anti-)de Sitter Gravity

We show that the asymptotic dynamics of two-dimensional de Sitter or anti-de Sitter Jackiw-Teitelboim (JT) gravity is described by a generalized two-particle Calogero-Sutherland model. This correspondence is established by formulating the JT model of (A)dS gravity in two dimensions as a topological gauge theory, which reduces to a nonlinear 0+1-dimensional sigma model on the boundary of (A)dS space. The appearance of cyclic coordinates allows then a further reduction to the Calogero-Sutherland quantum mechanical model.

hep-th↗

arXiv2002

Some Aspects of the de Sitter/CFT Correspondence

We discuss several aspects of the proposed correspondence between quantum gravity on de Sitter spaces and Euclidean conformal field theories. The central charge appearing in the asymptotic symmetry algebra of three-dimensional de Sitter space is derived both from the conformal anomaly and the transformation law of the CFT stress tensor when going from dS_3 in planar coordinates to dS_3 with cosmological horizon. The two-point correlator for CFT operators coupling to bulk scalars is obtained in static coordinates, corresponding to a CFT on a cylinder. Correlation functions are also computed for CFTs on two-dimensional hyperbolic space. We furthermore determine the energy momentum tensor and the Casimir energy of the conformal field theory dual to the Schwarzschild-de Sitter solution in five dimensions. Requiring the pressure to be positive yields an upper bound for the black hole mass, given by the mass of the Nariai solution. Beyond that bound, which is similar to the one found by Strominger requiring the conformal weights of CFT operators to be real, one encounters naked singularities.

hep-th↗

arXiv2001

The Asymptotic Dynamics of de Sitter Gravity in three Dimensions

We show that the asymptotic dynamics of three-dimensional gravity with positive cosmological constant is described by Euclidean Liouville theory. This provides an explicit example of a correspondence between de Sitter gravity and conformal field theories. In the case at hand, this correspondence is established by formulating Einstein gravity with positive cosmological constant in three dimensions as an SL(2,C) Chern-Simons theory. The de Sitter boundary conditions on the connection are divided into two parts. The first part reduces the CS action to a nonchiral SL(2,C) WZNW model, whereas the second provides the constraints for a further reduction to Liouville theory, which lives on the past boundary of dS_3.

hep-th↗

arXiv2000

Dualities in D=5, N=2 Supergravity, Black Hole Entropy, and AdS Central Charges

The issue of microstate counting for general black holes in D=5, N=2 supergravity coupled to vector multiplets is discussed from various viewpoints. The statistical entropy is computed for the near-extremal case by using the central charge appearing in the asymptotic symmetry algebra of AdS_2. Furthermore, we show that the considered supergravity theory enjoys a duality invariance which connects electrically charged black holes and magnetically charged black strings. The near-horizon geometry of the latter turns out to be AdS_3 x S^2, which allows a microscopic calculation of their entropy using the Brown-Henneaux central charges in Cardy's formula. In both approaches we find perfect agreement between statistical and thermodynamical entropy.

hep-th↗