arXiv subjects

Dietmar Klemm

Publications and source records attributed to Dietmar Klemm.

62 records · Page 4Linked to original sources

arXiv2000

w_{\infty} Algebras, Conformal Mechanics, and Black Holes

We discuss BPS solitons in gauged ${\cal N}=2$, D=4 supergravity. The solitons represent extremal black holes interpolating between different vacua of anti-de Sitter spaces. The isometry superalgebras are determined and the motion of a superparticle in the extremal black hole background is studied and confronted with superconformal mechanics. We show that the Virasoro symmetry of conformal mechanics, which describes the dynamics of the superparticle near the horizon of the extremal black hole under consideration, extends to a symmetry under the $w_{\infty}$ algebra of area-preserving diffeomorphisms. We find that a Virasoro subalgebra of $w_{\infty}$ can be associated to the Virasoro algebra of the asymptotic symmetries of $AdS_2$. In this way spacetime diffeomorphisms of $AdS_2$ translate into diffeomorphisms in phase space: our system offers an explicit realization of the $AdS_2/CFT_1$ correspondence. Using the dimensionally reduced action, the central charge is computed. Finally, we also present generalizations of superconformal mechanics which are invariant under ${\cal N} =1$ and ${\cal N} =2$ superextensions of $w_{\infty}$.

hep-th↗

arXiv1999

Thermodynamics of Kerr-Newman-AdS Black Holes and Conformal Field Theories

We study the thermodynamics of four-dimensional Kerr-Newman-AdS black holes both in the canonical and the grand-canonical ensemble. The stability conditions are investigated, and the complete phase diagrams are obtained, which include the Hawking-Page phase transition in the grand-canonical ensemble. In the canonical case, one has a first order transition between small and large black holes, which disappears for sufficiently large electric charge or angular momentum. This disappearance corresponds to a critical point in the phase diagram. Via the AdS/CFT conjecture, the obtained phase structure is also relevant for the corresponding conformal field theory living in a rotating Einstein universe, in the presence of a global background U(1) current. An interesting limit arises when the black holes preserve some supersymmetry. These BPS black holes correspond to highly degenerate zero temperature states in the dual CFT, which lives in an Einstein universe rotating with the speed of light.

hep-th↗

arXiv1999

M-Theory and Stringy Corrections to Anti-de Sitter Black Holes and Conformal Field Theories

We consider black holes in anti-de Sitter space AdS_{p+2} (p = 2,3,5), which have hyperbolic, flat or spherical event horizons. The $O(α'^3)$ corrections (or the leading corrections in powers of the eleven-dimensional Planck length) to the black hole metrics are computed for the various topologies and dimensions. We investigate the consequences of the stringy or M-theory corrections for the black hole thermodynamics. In particular, we show the emergence of a stable branch of small spherical black holes. We obtain the corrected Hawking-Page transition temperature for black holes with spherical horizons, and show that for p=3 this phase transition disappears at a value of $α'$ considerably smaller than that estimated previously by Gao and Li. Using the AdS/CFT correspondence, we determine the $S^1 x S^3$ N=4 SYM phase diagram for sufficiently large `t Hooft coupling, and show that the critical point at which the Hawking-Page transition disappears (the correspondence point of Horowitz-Polchinski), occurs at $g_{YM}^2N \approx 20.5$. The d=4 and d=7 black hole phase diagrams are also determined, and connection is made with the corresponding boundary CFTs. Finally, for flat and hyperbolic horizons, we show that the leading stringy or M-theory corrections do not give rise to any phase transition. For horizons compactified to a torus $T^p$ or to a quotient of hyperbolic space, $H^p/Γ$, we comment on the effects of light winding modes.

hep-th↗

arXiv1999

BPS Black Holes in Gauged N=4, D=4 Supergravity

We find solutions of the bosonic sector of gauged N=4, D=4 SU(2) $\times$ SU(2) supergravity, which represent dilaton black holes with toroidal or spherical event horizons. The axion is consistently truncated, and the gauge group is broken to U(1) $\times$ U(1). The spherical black holes carry two electric and two magnetic abelian charges, whereas the toroidal holes have vanishing magnetic charges. The spacetime metrics are warped products, and the manifolds turn out to be globally hyperbolic, in contrast to standard gauged supergravity ground states. It is shown that in the toroidal case, there are solutions preserving one quarter or one half of the supersymmetries, while for spherical topologies all supersymmetries are broken. In general, the toroidal BPS states represent naked singularities, but there is also a supersymmetric black hole with vanishing Hawking temperature. The 1/2 supersymmetric case arises for vanishing charges and mass, and represents the known domain wall solution of the Freedman-Schwarz model. It provides the background in which the black holes live. Finally, we use Chamseddine's and Volkov's Kaluza-Klein interpretation of gauged N=4, D=4 SU(2) $\times$ SU(2) supergravity to lift our solutions to ten and eleven dimensions and to consider them as solutions to the leading order equations of motion of the string-/M-theory effective action.

hep-th↗

arXiv1999

Supersymmetry of Anti-de Sitter Black Holes

We examine supersymmetry of four-dimensional asymptotically anti-de Sitter (AdS) dyonic black holes in the context of gauged N=2 supergravity. Our calculations concentrate on black holes with unusual topology and their rotating generalizations, but we also reconsider the spherical rotating dyonic Kerr-Newman-AdS black hole, whose supersymmetry properties have previously been investigated by Kostelecký and Perry within another approach. We find that in the case of spherical, toroidal or cylindrical event horizon topology, the black holes must rotate in order to preserve some supersymmetry; the non-rotating supersymmetric configurations representing naked singularities. However, we show that this is no more true for black holes whose event horizons are Riemann surfaces of genus $g>1$, where we find a nonrotating extremal solitonic black hole carrying magnetic charge and permitting one Killing spinor. For the nonrotating supersymmetric configurations of various topologies, all Killing spinors are explicitly constructed.

hep-th↗

arXiv1998

Rotating Black Branes wrapped on Einstein Spaces

We present new rotating black brane solutions which solve Einstein's equations with cosmological constant $Λ$ in arbitrary dimension $d$. For negative $Λ$, the branes naturally appear in AdS supergravity compactifications, and should therefore play some role in the AdS/CFT correspondence. The spacetimes are warped products of a four-dimensional part and an Einstein space of dimension $d-4$, which is not necessarily of constant curvature. As a special subcase, the solutions contain the higher dimensional generalization of the Kerr-AdS metric recently found by Hawking et al.

hep-th↗

arXiv1998

Topological Black Holes in Weyl Conformal Gravity

We present a class of exact solutions of Weyl conformal gravity, which have an interpretation as topological black holes. Solutions with negative, zero or positive scalar curvature at infinity are found, the former generalizing the well-known topological black holes in anti-de Sitter gravity. The rather delicate question of thermodynamic properties of such objects in Weyl conformal gravity is discussed; suggesting that the thermodynamics of the found solutions should be treated within the framework of gravity as an induced phenomenon, in the spirit of Sakharov's work.

gr-qc↗

arXiv1998

Quantum Properties of Topological Black Holes

We examine quantum properties of topological black holes which are asymptotically anti--de Sitter. First, massless scalar fields and Weyl spinors which propagate in the background of an anti--de Sitter black hole are considered in an exactly soluble two--dimensional toy model. The Boulware--, Unruh--, and Hartle--Hawking vacua are defined. The latter results to coincide with the Unruh vacuum due to the boundary conditions necessary in asymptotically adS spacetimes. We show that the Hartle--Hawking vacuum represents a thermal equilibrium state with the temperature found in the Euclidean formulation. The renormalized stress tensor for this quantum state is well--defined everywhere, for any genus and for all solutions which do not have an inner Cauchy horizon, whereas in this last case it diverges on the inner horizon. The four--dimensional case is finally considered, the equilibrium states are discussed and a luminosity formula for the black hole of any genus is obtained. Since spacelike infinity in anti--de Sitter space acts like a mirror, it is pointed out how this would imply information loss in gravitational collapse. The black hole's mass spectrum according to Bekenstein's view is discussed and compared to that provided by string theory.

gr-qc↗