[Show abstract][Hide abstract] ABSTRACT: The 3-d 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 light-cone gauging (Liouville model) whereas in the IR it is a space-like gauging
(2-d black hole).
[Show abstract][Hide abstract] ABSTRACT: In this talk, I will summarize recent developments in 5-dimensional 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 5-dimensional supersymmetric stationary solutions.
Preview · Article · May 2006 · Fortschritte der Physik
[Show abstract][Hide abstract] ABSTRACT: We present a comprehensive classification of supersymmetric vacua of M-theory compactification on seven-dimensional manifolds with general four-form fluxes. We analyze the cases where the resulting four-dimensional 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 space-time 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 Einstein-Sasaki and no internal fluxes are allowed. Moreover, we provide a new vacuum with N = 1 supersymmetry and SU(3) structure, where all fluxes are non-zero and the first order differential equations are solved.
[Show abstract][Hide abstract] ABSTRACT: Based on recent proposals linking four and five-dimensional 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–Taub-NUT spacetime. Then we consider corrections to the 4D solutions associated with more general prepotentials and comment on analogous corrections on the 5D side.
[Show abstract][Hide abstract] ABSTRACT: We derive conditions for the existence of four-dimensional 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 four-dimensional cosmological constant, while negative, becomes small in the vacuum with the weak string coupling.
Preview · Article · Aug 2005 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: In order to lift the continuous moduli space of string vacua, non-trivial fluxes may be the essential input. In this talk I summarize aspects of two approaches to compactifications in the presence of fluxes: (i) generalized Scherk-Schwarz reductions and gauged supergravity and (ii) the description of flux-deformed geometries in terms of G-structures 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 space-time and ...'' (Kolymbari, Crete, September 2004)
[Show abstract][Hide abstract] ABSTRACT: A supersymmetric vacuum has to obey a set of constraints on fluxes as well as first order differential equations defined by the G-structures of the internal manifold. We solve these equations for type IIB supergravity with SU(3) structures. The 6-dimensional internal manifold has to be complex, the axion/dilaton is in general non-holomorphic 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 flow-type solution and near poles and zeros we find the so-called type-A and type-B vacuum. Comment: 29 pages, minor corrections, version published in NPB
[Show abstract][Hide abstract] ABSTRACT: We study conditions on general fluxes of massive Type IIA supergravity that lead to four-dimensional 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 three-form and four-form fluxes. We further discuss the implications of such flux vacua with added intersecting D6-branes, leading to the chiral non-Abelian 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 four-dimensional (chiral) N = 1 supersymmetric solutions of massive Type IIA supergravity with D-branes and fluxes, compactified on orientifolds.
[Show abstract][Hide abstract] ABSTRACT: We discuss supersymmetric black holes embedded in a Gödel-type universe with cosmological constant in five dimensions. The spacetime is a fibration over a four-dimensional 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 super-Yang–Mills theory. Finally, a Gödel–de Sitter universe is also presented and its causal structure is discussed.
Preview · Article · Aug 2004 · Classical and Quantum Gravity
[Show abstract][Hide abstract] ABSTRACT: We consider compactifications of M-theory on 7-manifolds in the presence of 4-form fluxes, which leave at least four supercharges unbroken. We focus especially on the case, where the fluxes on the 7-manifold 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 4-dimensional cosmological constant (or superpotential).
[Show abstract][Hide abstract] ABSTRACT: We consider compactifications of M-theory on 7-manifolds in the presence of 4-form fluxes, which leave at least four supercharges unbroken. Supersymmetric vacua admit G-structures 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 4-dimensional cosmological constant (i.e. superpotential).
[Show abstract][Hide abstract] ABSTRACT: We show that the Godel solution of five-dimensional gauged supergravity contains either closed time-like curves through every space-time 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 four-dimensional 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.
[Show abstract][Hide abstract] ABSTRACT: In flux compactifications of M-theory a superpotential is generated whose explicit form depends on the structure group of the 7-dimensional 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 non-zero flux components entering the superpotential describe an effective 1-dimensional model and a Chern-Simons model if there are SU(2) structures. Comment: 10 pages
Preview · Article · Jan 2004 · Classical and Quantum Gravity
[Show abstract][Hide abstract] 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 typos
Preview · Article · Dec 2003 · Journal of High Energy Physics
[Show abstract][Hide abstract] ABSTRACT: We study N=1 supersymmetric four-dimensional solutions of massive Type IIA supergravity with intersecting D6-branes in the presence NS-NS three-form fluxes. We derive N=1 supersymmetry conditions for the D6-brane 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 D6-branes wrap supersymmetric three-cycles 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 D6-branes intersect at angles of SU(2) rotations; non-zero mass parameter corresponds to D8-branes which are orthogonal to the common cycle of all D6-branes. The anomaly inflow indicates that the gauge theory on intersecting (massive) D6-branes is not chiral. Comment: 31 pages, Latex, small changes, add refs
[Show abstract][Hide abstract] ABSTRACT: In this talk I discuss intersecting brane configurations coming from explicit metrics with G2 holonomy. An example of a 7-manifold which representing a bundle over a self-dual Einstein space is described and the potential appearing after compactification over the 6-d twistor space is derived.
Preview · Article · Jul 2003 · Fortschritte der Physik
[Show abstract][Hide abstract] ABSTRACT: We obtain a general class of time-dependent, asymptotically de Sitter backgrounds which solve the first order bosonic equations that extremize the action for supergravity with gauged non-compact $R$-symmetry. These backgrounds correspond only to neutral fields with the correct sign of kinetic energy. Within N=2 five-dimensional supergravity with vector-superfields we provide examples of multi-centered charged black holes in asymptotic de Sitter space, whose spatial part is given by a time-dependent hyper-K\"ahler space. Reducing these backgrounds to four dimensions yields asymptotically de Sitter multi-centered charged black hole backgrounds and we show that they are related to an instanton configuration by a massive T-duality over time. Within N=2 gauged supergravity in four (and five)-dimensions with hyper-multiplets 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 references
Preview · Article · Mar 2003 · Classical and Quantum Gravity
[Show abstract][Hide abstract] ABSTRACT: We consider warp compactifications of M-theory on 7-manifolds in the presence of 4-form fluxes and investigate the constraints imposed by supersymmetry. As long as the 7-manifold supports only one Killing spinor we infer from the Killing spinor equations that non-trivial 4-form fluxes will necessarily curve the external 4-dimensional space. On the other hand, if the 7-manifold has at least two Killing spinors, there is a non-trivial Killing vector yielding a reduction of the 7-manifold to a 6-manifold and we confirm that 4-form fluxes can be incorporated if one includes non-trivial SU(3) structures. Comment: 13 pages, Latex; minor changes & add references
Preview · Article · Feb 2003 · Journal of High Energy Physics
[Show abstract][Hide abstract] ABSTRACT: We discuss a new family of metrics of 7-manifolds with G(2) holonomy, which are R-3 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 co-dimension four fixed points which yield upon compactification only intersecting D6-branes if one also identifies two parameters. Two of the remaining parameters are quantized and we argue that they are related to the number of D6-branes, which appear in three stacks. We perform explicitly the reduction to the type IIA model.
Preview · Article · Aug 2002 · Journal of High Energy Physics
[Show abstract][Hide abstract] 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 space-time in the transverse direction that is cut off at a critical distance, governed by the magnitude of the negative cosmological constant on the wall.
No preview · Article · Jun 2002 · Physical Review D