Publications (89)314.42 Total impact

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ABSTRACT: The 3d BTZ black hole represents an orbifold of AdS 3 gravity. The UV as well as the IR region of the CFT is governed by a gauged SL(2, R) WZW model. In the UV it corresponds to a lightcone gauging (Liouville model) whereas in the IR it is a spacelike gauging (2d black hole).05/2007: pages 264270; 
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ABSTRACT: In this talk, I will summarize recent developments in 5dimensional supergravity. This includes a discussion about black ring solutions, we will see how one can construct regular (bubbling) solutions with the same charges as black holes and finally will explore the close relationship between 4 and 5dimensional supersymmetric stationary solutions.Fortschritte der Physik 05/2006; 54(5‐6):275  281. DOI:10.1002/prop.200510273 · 1.23 Impact Factor 
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ABSTRACT: We present a comprehensive classification of supersymmetric vacua of Mtheory compactification on sevendimensional manifolds with general fourform fluxes. We analyze the cases where the resulting fourdimensional vacua have N = 1,2,3,4 supersymmetry and the internal space allows for SU(2), SU(3) or G_2 structures. In particular, we find for N = 2 supersymmetry, that the external spacetime is Minkowski and the base manifold of the internal space is conformally K\"ahler for SU(2) structures, while for SU(3) structures the internal space has to be EinsteinSasaki and no internal fluxes are allowed. Moreover, we provide a new vacuum with N = 1 supersymmetry and SU(3) structure, where all fluxes are nonzero and the first order differential equations are solved.Nuclear Physics B 01/2006; DOI:10.1016/j.nuclphysb.2006.04.018 · 3.95 Impact Factor 
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ABSTRACT: Based on recent proposals linking four and fivedimensional BPS solutions, we discuss the explicit dictionary between general stationary 4D and 5D supersymmetric solutions in N=2 supergravity theories with cubic prepotentials. All these solutions are completely determined in terms of the same set of harmonic functions and the same set of attractor equations. As an example, we discuss black holes and black rings in Gödel–TaubNUT spacetime. Then we consider corrections to the 4D solutions associated with more general prepotentials and comment on analogous corrections on the 5D side.Nuclear Physics B 01/2006; DOI:10.1016/j.nuclphysb.2005.10.026 · 3.95 Impact Factor 
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ABSTRACT: We derive conditions for the existence of fourdimensional N=1 supersymmetric flux vacua of massive type IIA string theory with general supergravity fluxes turned on. For an SU(3) singlet Killing spinor, we show that such flux vacua exist when the internal geometry is nearly Kähler. The geometry is not warped, all the allowed fluxes are proportional to the mass parameter, and the dilaton is fixed by a ratio of (quantized) fluxes. The fourdimensional cosmological constant, while negative, becomes small in the vacuum with the weak string coupling.Physical Review Letters 08/2005; 95(2):021601. DOI:10.1103/PhysRevLett.95.021601 · 7.73 Impact Factor 
Article: Stabilization of moduli by fluxes
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ABSTRACT: In order to lift the continuous moduli space of string vacua, nontrivial fluxes may be the essential input. In this talk I summarize aspects of two approaches to compactifications in the presence of fluxes: (i) generalized ScherkSchwarz reductions and gauged supergravity and (ii) the description of fluxdeformed geometries in terms of Gstructures and intrinsic torsion. Comment: 22 pages, added refs., to appear in proceedings of: ``Strings and Cosmology'', (Texas A&M University, March 2004) and the RTN workshop: ``The quantum structure of spacetime and ...'' (Kolymbari, Crete, September 2004)07/2005; 53(78). DOI:10.1002/prop.200410208 
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ABSTRACT: A supersymmetric vacuum has to obey a set of constraints on fluxes as well as first order differential equations defined by the Gstructures of the internal manifold. We solve these equations for type IIB supergravity with SU(3) structures. The 6dimensional internal manifold has to be complex, the axion/dilaton is in general nonholomorphic and a cosmological constant is only possible if the SU(3) structures are broken to SU(2) structures. The general solution is expressed in terms of one function which is holomorphic in the three complex coordinates and if this holomorphic function is constant, we obtain a flowtype solution and near poles and zeros we find the socalled typeA and typeB vacuum. Comment: 29 pages, minor corrections, version published in NPBNuclear Physics B 02/2005; DOI:10.1016/j.nuclphysb.2005.05.020 · 3.95 Impact Factor 
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ABSTRACT: We study conditions on general fluxes of massive Type IIA supergravity that lead to fourdimensional backgrounds with N = 1 supersymmetry. We derive these conditions in the case of SU(3) as well as SU(2)structures. SU(3)structures imply that the internal space is constrained to be a nearly K\"ahler manifold with all the turned on fluxes, and the negative cosmological constant proportional to the mass parameter, and the dilaton fixed by the quantized ratio of the threeform and fourform fluxes. We further discuss the implications of such flux vacua with added intersecting D6branes, leading to the chiral nonAbelian gauge sectors (without orientifold projections). Examples that break SU(3)structures to SU(2)ones allow for the internal space conformally flat (up to orbifold and orientifold projections), for which we give an explicit example. These results provide a starting point for further study of the fourdimensional (chiral) N = 1 supersymmetric solutions of massive Type IIA supergravity with Dbranes and fluxes, compactified on orientifolds.Nuclear Physics B 08/2004; DOI:10.1016/j.nuclphysb.2004.12.004 · 3.95 Impact Factor 
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ABSTRACT: We discuss supersymmetric black holes embedded in a Gödeltype universe with cosmological constant in five dimensions. The spacetime is a fibration over a fourdimensional Kähler base manifold, and generically has closed timelike curves. Asymptotically the space approaches a deformation of AdS5, which suggests that the appearance of closed timelike curves should have an interpretation in some deformation of superYang–Mills theory. Finally, a Gödel–de Sitter universe is also presented and its causal structure is discussed.Classical and Quantum Gravity 08/2004; 21(17):4107. DOI:10.1088/02649381/21/17/006 · 3.10 Impact Factor 
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ABSTRACT: We consider compactifications of Mtheory on 7manifolds in the presence of 4form fluxes, which leave at least four supercharges unbroken. We focus especially on the case, where the fluxes on the 7manifold are consistent with SU(3) singlet spinors and hence appear as specific SU(3) structures. We derive the constraints on the fluxes imposed by supersymmetry and determine the flux components that fix the resulting 4dimensional cosmological constant (or superpotential).Nuclear Physics B 08/2004; DOI:10.1016/j.nuclphysb.2004.06.028 · 3.95 Impact Factor 
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ABSTRACT: We consider compactifications of Mtheory on 7manifolds in the presence of 4form fluxes, which leave at least four supercharges unbroken. Supersymmetric vacua admit Gstructures and we discuss the cases of G_2, SU(3) as well as SU(2)structures. We derive the constraints on the fluxes imposed by supersymmetry and determine the flux components that fix the resulting 4dimensional cosmological constant (i.e. superpotential). 
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ABSTRACT: We show that the Godel solution of fivedimensional gauged supergravity contains either closed timelike curves through every spacetime point or none at all, dependent on the rotational parameter. In addition, we present a deformation of that solution with a parameter kappa which characterizes the symmetry of fourdimensional base space: for kappa = 1, 0,  1 it has spherical, flat and hyperbolic symmetry, respectively. Also investigated are the causal properties of the lifted solution in 10 dimensions.Physics Letters B 01/2004; 580(12580):16. DOI:10.1016/j.physletb.2003.11.033 · 6.02 Impact Factor 
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ABSTRACT: In flux compactifications of Mtheory a superpotential is generated whose explicit form depends on the structure group of the 7dimensional internal manifold. In this note, we discuss superpotentials for the structure groups: G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For SU(3) structures, the nonzero flux components entering the superpotential describe an effective 1dimensional model and a ChernSimons model if there are SU(2) structures. Comment: 10 pagesClassical and Quantum Gravity 01/2004; DOI:10.1088/02649381/21/10/026 · 3.10 Impact Factor 
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ABSTRACT: Typical de Sitter (dS) vacua of gauged supergravity correspond to saddle points of the potential and often the unstable mode runs into a singularity. We explore the possibility to obtain dS points where the unstable mode goes on both sides into a supersymmetric smooth vacuum. Within N=2 gauged supergravity coupled to the universal hypermultiplet, we have found a potential which has two supersymmetric minima (one of them can be flat) and these are connected by a de Sitter saddle point. In order to obtain this potential by an Abelian gauging, it was important to include the recently proposed quantum corrections to the universal hypermultiplet sector. Our results apply to four as well as five dimensional gauged supergravity theories. Comment: 25 pages, 1 figure, add refs and corrected typosJournal of High Energy Physics 12/2003; DOI:10.1088/11266708/2004/01/068 · 6.22 Impact Factor 
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ABSTRACT: We study N=1 supersymmetric fourdimensional solutions of massive Type IIA supergravity with intersecting D6branes in the presence NSNS threeform fluxes. We derive N=1 supersymmetry conditions for the D6brane and flux configurations in an internal manifold $X_6$ and derive the intrinsic torsion (or SU(3)structure) related to the fluxes. In the absence of fluxes, N=1 supersymmetry implies that D6branes wrap supersymmetric threecycles of $X_6$ that intersect at angles of SU(3) rotations and the geometry is deformed by SU(3)structures. The presence of fluxes breaks the SU(3) structures to SU(2) and the D6branes intersect at angles of SU(2) rotations; nonzero mass parameter corresponds to D8branes which are orthogonal to the common cycle of all D6branes. The anomaly inflow indicates that the gauge theory on intersecting (massive) D6branes is not chiral. Comment: 31 pages, Latex, small changes, add refsNuclear Physics B 08/2003; DOI:10.1016/j.nuclphysb.2003.10.028 · 3.95 Impact Factor 
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ABSTRACT: We obtain a general class of timedependent, asymptotically de Sitter backgrounds which solve the first order bosonic equations that extremize the action for supergravity with gauged noncompact $R$symmetry. These backgrounds correspond only to neutral fields with the correct sign of kinetic energy. Within N=2 fivedimensional supergravity with vectorsuperfields we provide examples of multicentered charged black holes in asymptotic de Sitter space, whose spatial part is given by a timedependent hyperK\"ahler space. Reducing these backgrounds to four dimensions yields asymptotically de Sitter multicentered charged black hole backgrounds and we show that they are related to an instanton configuration by a massive Tduality over time. Within N=2 gauged supergravity in four (and five)dimensions with hypermultiplets there could also be neutral cosmological backgrounds that are regular and correspond to the different de Sitter spaces at early and late times. Comment: 28 pages, Latex; minor changes and add referencesClassical and Quantum Gravity 03/2003; DOI:10.1088/02649381/20/19/304 · 3.10 Impact Factor 
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ABSTRACT: We consider warp compactifications of Mtheory on 7manifolds in the presence of 4form fluxes and investigate the constraints imposed by supersymmetry. As long as the 7manifold supports only one Killing spinor we infer from the Killing spinor equations that nontrivial 4form fluxes will necessarily curve the external 4dimensional space. On the other hand, if the 7manifold has at least two Killing spinors, there is a nontrivial Killing vector yielding a reduction of the 7manifold to a 6manifold and we confirm that 4form fluxes can be incorporated if one includes nontrivial SU(3) structures. Comment: 13 pages, Latex; minor changes & add referencesJournal of High Energy Physics 02/2003; DOI:10.1088/11266708/2003/04/002 · 6.22 Impact Factor 
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ABSTRACT: In this talk I discuss intersecting brane configurations coming from explicit metrics with G2 holonomy. An example of a 7manifold which representing a bundle over a selfdual Einstein space is described and the potential appearing after compactification over the 6d twistor space is derived.Fortschritte der Physik 01/2003; 51(7‐8):664  669. DOI:10.1002/prop.200310080 · 1.23 Impact Factor 
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ABSTRACT: We discuss a new family of metrics of 7manifolds with G(2) holonomy, which are R3 bundles over a quaternionic space. The metrics depend on five parameters and have two abelian isometries. Certain singularities of the G(2) manifolds are related to fixed points of these isometries; there are two combinations of Killing vectors that possess codimension four fixed points which yield upon compactification only intersecting D6branes if one also identifies two parameters. Two of the remaining parameters are quantized and we argue that they are related to the number of D6branes, which appear in three stacks. We perform explicitly the reduction to the type IIA model.Journal of High Energy Physics 08/2002; DOI:10.1088/11266708/2002/08/027 · 6.22 Impact Factor 
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ABSTRACT: Within D=5, N=2 gauged supergravity coupled to hypermultiplets we derive consistency conditions for BPS domain walls with a constant negative curvature on the wall. For such wall solutions to exist, the covariant derivative of the projector, governing the constraint on the Killing spinor, has to be nonzero and proportional to the cosmological constant on the domain walls. We also prove that in this case solutions of the Killing spinor equations are indeed solutions of the equations of motion. We present explicit, analytically solved examples of such domain walls, employing the universal hypermultiplet fields. These examples involve the running of two scalar fields and the spacetime in the transverse direction that is cut off at a critical distance, governed by the magnitude of the negative cosmological constant on the wall.Physical Review D 06/2002; 65(12). DOI:10.1103/PhysRevD.65.126007 · 4.86 Impact Factor
Publication Stats
3k  Citations  
314.42  Total Impact Points  
Top Journals
Institutions

1991–2007

HumboldtUniversität zu Berlin
 Department of Physics
Berlín, Berlin, Germany


2005–2006

LudwigMaximilianUniversity of Munich
 Arnold Sommerfeld Center for Theoretical Physics (ASC)
München, Bavaria, Germany


2004–2005

University of Pennsylvania
 Department of Physics and Astronomy
Filadelfia, Pennsylvania, United States


2002–2004

Max Planck Institute for Gravitational Physics (AlbertEinsteinInstitute)
Potsdam, Brandenburg, Germany


2000

University of California, Santa Barbara
Santa Barbara, California, United States 
University of Southern California
Los Angeles, California, United States


1999–2000

California Institute of Technology
 Department of Physics
Pasadena, California, United States


1994–1998

Stanford University
 Department of Physics
Palo Alto, California, United States
