P. Marios Petropoulos

Three-dimensional black holes from deformed anti de Sitter

We present new exact three-dimensional black-string backgrounds, which contain both NS-NS and electromagnetic fields, and generalize the BTZ black holes and the black string studied by Horne and Horowitz. They are obtained as deformations of the SL(2,) WZW model. Black holes resulting from purely continuous deformations possess true curvature singularities. When discrete identifications are introduced, extra chronological singularities appear, which under certain circumstances turn out to be naked. The backgrounds at hand appear in the moduli space of the SL(2,) WZW model. Hence, they provide exact string backgrounds and allow for a more algebraical (CFT) description. This makes possible the determination of the spectrum of primaries.

Axionic symmetry gaugings in N = 4 supergravities and their higher-dimensional origin

We study the class of four-dimensional N = 4 supergravities obtained by gauging the axionic shift and axionic rescaling symmetries. We formulate these theories using the machinery of embedding tensors, characterize the full gauge algebras and discuss several specic features of this family of gauged supergravities. We exhibit in particular a generalized duality between massive vectors and massive two-forms in four dimensions, inherited from the gauging of the shift symmetry. We show that these theories can be deduced from higher dimensions by a Scherk{Schwarz reduction, where a twist with respect to a non-compact symmetry is required. The four-dimensional generalized duality plays a crucial role in identifying the higher-dimensional ascendent.

Some remarks on anti-de Sitter D-branes

We present some preliminary investigations about the AdS2 × S2 D3-branes in AdS3 × S3. We analyse the quadratic fluctuations of the Dirac-Born- Infeld action around a given semi-classical D-brane configuration and compare them with results obtained by using conformal-field-theory techniques. We finally study classical motions of open strings attached to those D-branes and analyse the role of the spectral flow in this context.

Holographic Fluids with Vorticity and Analogue Gravity

A bstractWe study holographic three-dimensional fluids with vorticity in local equilibrium and discuss their relevance to analogue gravity systems. The Fefferman-Graham expansion leads to the fluid’s description in terms of a comoving and rotating Papapetrou- Randers frame. A suitable Lorentz transformation brings the fluid to the non-inertial Zermelo frame, which clarifies its interpretation as moving media for light/sound propagation. We apply our general results to the Lorentzian Kerr-AdS4 and Taub-NUT-AdS4 geometries that describe fluids in cyclonic and vortex flows respectively. In the latter case we associate the appearance of closed timelike curves to analogue optical horizons. In addition, we derive the classical rotational Hall viscosity of three-dimensional fluids with vorticity. Our formula remarkably resembles the corresponding result in magnetized plasmas.

Non-perturbative triality in heterotic and type II N=2 strings

Abstract The non-perturbative equivalence of four-dimensional N = 2 superstrings with three vector multiplets and four hypermultiplets is analysed. These models are obtained through freely acting orbifold compactifications from the heterotic, the symmetric and the asymmetric type II strings. The heterotic scalar manifolds are (SU(1, 1)/U(1))3 for the S, T, U moduli sitting in the vector multiplets and SO(4, 4)/(SO(4) × SO(4)) for those in the hypermultiplets. The type II symmetric duals correspond to a self-mirror Calabi-Yau threefold compactification with Hodge numbers h1,1 = h2,1 = 3, while the type II asymmetric construction corresponds to a spontaneous breaking of the N = (4,4) supersymmetry to N = (2, 0). Both have already been considered in the literature. The heterotic construction instead is new and we show that there is a weak/strong coupling S-duality relation between the heterotic and the asymmetric type IIA ground state with 4πSHet = −(4πSAs)−1; we also show that there is a partial restoration of N = 8 supersymmetry in the heterotic strong-coupling regime. We compute the full (non-)perturbative R2 and F2 corrections and determine the prepotential.

STRING THEORY ON ADS3: SOME OPEN QUESTIONS

A tibial cutting guide includes upper and lower portions having patient-matched surfaces. The upper portion defines resection slots for forming resections about the tibial eminence. The lower portion defines two pin slots for receiving alignment pins such that in use the position of the resection slots relative to the tibial eminence can be adjusted by sliding the cutting guide along the alignment pins placed in the tibia through the pin slots. The lower portion defines a resection slot for guiding a saw blade to form a horizontal plateau resection, and two pin holes for receiving fixation pins. A method includes positioning a patient-matched cutting guide on the proximal tibia; intra-operatively adjusting the position of the cutting guide in two degrees of freedom by sliding the cutting guide along fixation pins placed in the tibia; and resecting the tibia about the tibial eminence.

Holographic Three-Dimensional Fluids with Nontrivial Vorticity

geometries give rise to a rotating fluid with vortex flow. The Randers and Zermelo formsof the boundary metrics provide alternative descriptions of the fluid by inertial co-moving or byaccelerated observers. Such fluids possess acoustic horizons. Moreover, light propagation on theboundary Taub–NUT fluid will encounter an optical horizon associated with closed timelike curves.In the latter case the Misner string introduces a multi-valuedness of the scalar fluctuations whichcan be attributed to the anyonic nature of the boundary vortex.

The Geroch group in Einstein spaces

Geroch?s solution-generating method is extended to the case of Einstein spaces, which possess a Killing vector and are thus asymptotically (locally) (anti) de Sitter. This includes the reduction to a three-dimensional coset space, the description of the dynamics in terms of a sigma-model and its transformation properties under the group, and the reconstruction of new four-dimensional Einstein spaces. The detailed analysis of the space of solutions is performed using the Hamilton?Jacobi method in the instance where the three-dimensional coset space is conformal to . The cosmological constant appears in this framework as a constant of motion and transforms under .

Holographic perfect fluidity, Cotton energy-momentum duality and transport properties

A bstractWe investigate background metrics for 2 + 1-dimensional holographic theories where the equilibrium solution behaves as a perfect fluid, and admits thus a thermodynamic description. We introduce stationary perfect-Cotton geometries, where the Cotton-York tensor takes the form of the energy-momentum tensor of a perfect fluid, i.e. they are of Petrov type Dt. Fluids in equilibrium in such boundary geometries have non-trivial vorticity. The corresponding bulk can be exactly reconstructed to obtain 3 + 1-dimensional stationary black-hole solutions with no naked singularities for appropriate values of the black-hole mass. It follows that an infinite number of transport coefficients vanish for holographic fluids. Our results imply an intimate relationship between black-hole uniqueness and holographic perfect equilibrium. They also point towards a Cotton/energy-momentum tensor duality constraining the fluid vorticity, as an intriguing boundary manifestation of the bulk mass/nut duality.

NS5-branes on an ellipsis and novel marginal deformations with parafermions

We consider NS5-branes distributed along the circumference of an ellipsis and explicitly construct the corresponding gravitational background. This provides a continuous line of deformations between the limiting cases, considered before, in which the ellipsis degenerates into a circle or into a bar. We show that a slight deformation of the background corresponding to a circle distribution into an ellipsoidal one is described by a novel non-factorizable marginal perturbation of bilinears of dressed parafermions. The latter are naturally defined for the circle case since, as it was shown in the past, the background corresponds to an orbifold of the exact conformal field theory coset model SU(2)/U(1) × SL(2,)/U(1). We explore the possibility to define parafermionic objects at generic points of the ellipsoidal families of backgrounds away from the circle point. We also discuss a new limiting case in which the ellipsis degenerates into two infinitely stretched parallel bars and show that the background is related to the Eguchi-Hanson metric, via T-duality.