# Joint seminars academic year: 2010-2011

### Jock McOrist (DAMPT)

Leuven - May 25, 2011

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, May 25, 2011 at 10:30

### Giulio Bonelli (SISSA)

Leuven - May 25, 2011

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, May 25, 2011 at 13:00

### Anatoly Konechny (Heriot-Watt University, Edinburgh)

VUB / ULB - May 11, 2011

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, May 11, 2011 at 13:00

### Randomized Wilson loops, reduced models and the large D expansion

Oleg Evnin (ITP, Beijing)

VUB / ULB - May 11, 2011

Reduced models are matrix integrals believed to be related to the large N limit of gauge theories. These integrals are known to simplify further when the number of matrices D (corresponding to the number of space-time dimensions in the gauge theory) becomes large. Even though this limit appears to be of little use for computing the standard rectangular Wilson loop (which always singles out two directions out of D), a meaningful large D limit can be defined for a randomized Wilson loop (in which all D directions contribute equally). I will discuss a proof-of-concept implementation of this approach for the simplest reduced model (the original Eguchi-Kawai model) and the simplest randomization of the Wilson loop (Brownian sum over random walks). The resulting averaged Wilson loop displays a scale behavior strongly reminiscent of the area law.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, May 11, 2011 at 10:30

### 2D gravity and Kahler metrics

Semyon Klevtsov (ULB)

VUB / ULB - May 04, 2011

The most well-known example of random geometry is provided by the Liouville theory of 2d gravity, which is defined by a path integral over a class of conformally equivalent two-dimensional metrics. We propose some new path integral measures, which are naturally suited for the spaces of Kahler metrics in two and higher dimensions. Relations of these measures to 2d gravity, Kahler geometry and random matrix models will be discussed.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, May 04, 2011 at 13:00

### Black Hole Enigmas in AdS3/CFT2

Borun Chowdhury (Amsterdam)

VUB / ULB - May 04, 2011

A new phase in the non-Cardy regime with U(1) × U(1) symmetry is found to exist in the D1D5 CFT at the orbifold point. The new phase is captured by the partition function but not by the elliptic genus. Thus it is possible that the new phase does not exist at the sugra point. However we show by explicit construction that a new phase with the same charges in fact does exist at the sugra point but with a lower entropy. This new phase is a BMPV black hole with a hair around it. The lower entropy suggests that some states are protected and may possibly be counted by a new index.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, May 04, 2011 at 10:30

### "Electroweak Vector Boson Production in Association with Jets at the LHC"

Lance Dixon (SLAC)

Leuven – April 2007, 2011

The production of W and Z bosons in association with multiple jets at hadron colliders probes important aspects of QCD dynamics, and forms an important class of backgrounds to new physics searches. With the increase in energy from the Tevatron to the LHC, new kinematic regions open up, in which weak bosons can be energetically subdominant to the jets. Because the LHC is a pp machine, W bosons are produced primarily left-handed, even at large transverse momentum, which strongly impacts their decays to leptons. Recently the production rates for W bosons with up to four additional jets, and Z bosons with up to three jets, have been computed at next-to-leading-order in QCD, allowing more precise theoretical predictions of these processes to confront the initial LHC data.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, April 27, 2011 at 13:00

### "Matrix models for random partitions: integrability and applications"

Alexander Alexandrov (CEA, Ecole Normale Superieure,ITEP)

Leuven – April 2007, 2011

I will discuss exact matrix integral representations for different sums over partitions. The characteristic feature of the obtained matrix models is the presence of logarithmic (or, vice versa, exponential) terms in the potential. Our derivation is based on the application of the higher Casimir operators. We use the obtained matrix integral representation of the basic sum to construct a matrix integral representation of the partition functions for simple topological string amplitudes equal to the Nekrasov sums for supersymmetric gauge theories.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, April 27, 2011 at 10:30

### "A non-compact elliptic genus "

Jan Troost (LPTENS Paris)

VUB/ULB – April 6, 2011

In this talk, I will motivate the study of two-dimensional conformal field theories with a continuous spectrum and bound states. I will discuss a first example of how to calculate a modular covariant torus amplitude in such theories. It will enable us to interpret the modular completion of a mock modular form in elementary physical terms.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, April 06, 2011 at 13:00

### "Monopole operators and dualities in 3d CS matter theories "

Mauricio Romo (UC Santa Barbara)

VUB/ULB – April 6, 2011

We present a semiclassical method to compute the precise moduli space of three dimensional Chern-Simons theories with matter by analyzing the classical BPS equations for the theory on the cylinder, which include classical solutions of magnetic monopole operators. These determine the chiral ring of the theory, and thus they provide the complete set of order parameters determining the classical vacua of the theory. We show that the proper quantization of these semiclassical solutions gives us the topology of moduli space. We illustrate it in simple examples: orbifolds of ABJM, both abelian and non-abelian and including discrete torsion. We also give a glimpse on the problems arising on the possible generalization of Seiberg-like dualities for 3d CS theories showing that the Berenstein-Douglas approach does not give dual pairs in general.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, April 06, 2011 at 10:30

### "Fusion of line operators, and quantum integrability in AdS/CFT"

Raphael Benichou (VUB)

Leuven – March 30, 2011

I will present recent progress in the understanding of two-dimensional sigma-models on the supergroup PSl(n|n). I will emphasize the relevance of these models to study quantum integrability in the AdS/CFT correspondence. In particular i will explain the computation of the fusion of some line operators, the transfer matrices, that encode an infinite number of conserved charges. This computation leads to a first-principle, perturbative derivation of the Hirota equation, which has been argued to provide a solution to the spectrum problem in N=4 SYM.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 30, 2011 at 13:00

### "Wall-Crossing from Moduli Dynamics "

Sungjay Lee (DAMTP)

Leuven – March 30, 2011

We formulate supersymmetric low energy dynamics for BPS dyons in strongly-coupled N=2 Seiberg-Witten theories, and derive wall-crossing formulae thereof. For BPS states made up of a heavy core state and n probe (halo) dyons around it, we derive a reliable supersymmetric moduli dynamics with 3n bosonic coordinates and 4n fermionic superpartners. Attractive interactions are captured via a set of supersymmetric potential terms, whose detail depends only on the charges and the special Kaehler data of the underlying N=2 theories. The small parameters that control the approximation are not electric couplings but the mass ratio between the core and the probe, as well as the distance to the marginal stability wall where the central charges of the probe and of the core align. Quantizing the dynamics, we construct BPS bound states and derive the primitive and the semi-primitive wall-crossing formulae from the first principle. We speculate on applications to line operators and Darboux coordinates, and also about extension to supergravity setting.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 30, 2011 at 10:30

### "Non-local F(R) gravity or SFT motivated cosmology"

Alexey Koshelev (VUB)

Leuven, March 23, 2011

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 23, 2011 at 13:00

### "Warped AdS/(C)FT correspondences and a digression on Chiral(og) gravity"

Stéphane Detournay (ULB)

Leuven, March 23, 2011

Recently, the gauge/gravity duality has expanded outside its original high-energy/string theory realm, in particular through the proposed Kerr/CFT and non-relativistic AdS/CFT correspondences. A common feature of these approaches is the appearance of the so-called three-dimensional Warped AdS spaces. The latter have furthermore been conjectured to be dual to 2d CFTs. I will review and discuss arguments for this proposal. On the way I will digress on the status of chiral (log) gravity as a candidate for a consistent theory of quantum gravity in 3 dimensions.

Place:: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 23, 2011 at 10:30

### "An action principle for Vasiliev's faur-dimensional higher-spin gravity"

Nicolas Boulanger (UMons)

VUB/ULB – March 16, 2011

We provide Vasiliev's fully nonlinear equations of motion for bosonic gauge fields in four spacetime dimensions with an Hamiltonian action principle. The generalized Hamiltonian contains two types of interaction freedoms: One set of functions that appears in the Q-structure of the generalized curvatures of the odd forms in the duality-extended system; and another set depending on the Lagrange multipliers, encoding a generalized Poisson structure, i.e. a set of polyvector fields of ranks two or higher in target space.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, March 16, 2011 at 13:00

### "Interpreting and eliminating infrared divergences via a local theory of observables in inflationary cosmology "

Diego Chialva (UMons)

VUB/ULB – March 16, 2011

I propose a solution to the infrared issue in inflationary cosmology via the concept of the locality of the observer. First, I give an introduction to the loop corrections to cosmological observables and to the standard lore about infrared divergences during inflation. Then, I prove that all the infrared divergences in gravitational loops arise from an unphysical hidden assumption in the standard formalism. Finally, I reformulate the formalism eliminating its unphysical points and show that there is no divergence and no dependence on any infrared cutoff or similar. Examples and pictures are provided!

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, March 16, 2011 at 10:30

### "Supersymmetry breaking in conifold throats"

Nick Halmagyi (LPTHE, Paris)

Leuven, March 9, 2011

I will present an outline of work done to compute non-supersymmetric deformations of the warped deformed conifold. Such supergravity solutions have applications to metastable SUSY breaking in four dimensional gauge theory and also to the string landscape.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 09, 2011 at 13:00

### " Massive and critical (super)gravities in d ≥ 3 "

Jan Rosseel (Groningen)

Leuven – March 9, 2011

In this talk, we will discuss (super)gravities in d=3 with higher-curvature terms, that allow for unitary propagation of massive spin 2 degrees of freedom. Apart from an ordinary Einstein-Hilbert term and a cosmological parameter, we include a Lorentz-Chern-Simons term and a specific curvature squared term, associating a mass parameter to both of these. This leads to the so-called General Massive Gravity theories, that include New Massive Gravity and Topological Massive Gravity as particular limits. We will discuss an N=1 supersymmetric version of General Massive Gravity and deduce for which values of the (mass) parameters the propagation of massive gravitons around a maximally symmetric background is unitary. We pay special attention to so-called critical points in the parameter space of these massive gravities. At these critical points, massive gravitons disappear from the spectrum and are replaced by so-called logarithmic modes. The resulting gravity theories were proposed to be dual to 2d logarithmic conformal field theories. We show that critical New Massive Gravity allows for an extension to higher dimensions, that might serve as gravity dual of higher-dimensional logarithmic conformal field theories.

Place: Leuven, Celestijnenlaan 200D 05.34

Time: Wednesday, March 09, 2011 at 10:30

### "Holographic Superconductors and Negative Refractive Index"

Massimo Siani (KUL)

VUB/ULB – March 2, 2011

Using holography, we study a model which exhibits the peculiar features of superconductivity on the strongly coupled field theory side. Beyond this surprising result, we show that the same model predicts the refractive index becoming negative at low frequencies and temperatures.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, March 02, 2011 at 13:00

### "A U-duality supermultiplet"

Martin Cederwall (Chalmers)

VUB/ULB – March 2, 2011

Is it possible to go beyond dimensional reduction without breaking U-duality? What would be the appropriate generalisation of the coset dynamics of the scalar fields? In order to investigate this issue in a concrete situation, we extend the coordinates of the internal manifold, in our case a T6, to transform under the appropriate representation of U-duality, and demand that supersymmetry is present. Dependence on the uncompactified coordinates is suppressed. Pure spinor cohomology, properly adapted to the symmetry at hand, naturally leads to a new type of linear supermultiplet, that is unusual in the sense that the equations of motion contain higher powers (up to four) of derivatives. The structure group is SU(8) × SU(2), with bosonic derivatives transforming as (28,1) and fermionic ones as (8,2). The supermultiplet and its gauge symmetries are described in detail in the linearised case.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, March 02, 2011 at 10:30

### "Holographic quantum criticality induced by magnetic fields"

Eric D'Hoker (UCLA)

Leuven – February 23, 2011

Using holography, we will study low temperature thermodynamics and low energy correlators in 3+1-dimensional gauge theories in the presence of an external magnetic field and finite charge density at strong coupling. We will exhibit a quantum phase transition, quantum critical behavior, and the emergence of 1+1-dimensional CFT in the RG flow of various correlators.

Place: Leuven, Celestijnenlaan 200D 06.32

Time: Wednesday, February 23, 2011 at 13:00

### "D-brane non-perturbative effects and geometric deformations"

Anatoly Dymarsky (Princeton)

Leuven – February 23, 2011

I will discuss how the non-perturbative effect (gaugino condensation) on D-branes is manifest in ten-dimensional geometry. It turns out that the corresponding D-brane backreacts on the surrounding geometry changing the complex and/or simplectic structure. The emphasis of the talk will be on the case of D7-brane as in this case the classical geometry changes into a genuine generalised geometry.

Place: Leuven, Celestijnenlaan 200D 06.32

Time: Wednesday, February 23, 2011 at 10:30

### "Static supersymmetric black holes in AdS4 with spherical symmetry "

Stefan Vandoren (Utrecht)

VUB/ULB - February 16, 2011

We present recently found static supersymmetric AdS4 black holes, and the 1/4 BPS constraints for spherical symmetry in N = 2 gauged supergravity in the presence of Fayet-Iliopoulos terms. The existence of a horizon is intimately related with the requirement that the scalars are not constant, but given in terms of harmonic functions in analogy to the attractor flow in ungauged supergravity. The black hole charges depend on the choice of the electromagnetic gauging, with only magnetic charges for purely electric gaugings. Finally we show how these black holes can be embedded in N = 8 supergravity and thus in M-theory.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, February 16, 2011 at 13:00

### "Negative refractive index and anti-M2 branes"

Davide Forcella (ULB)

VUB/ULB - February 16, 2011

The seminar will be divided in two non-related parts. In the first part I will briefly review some recent results related to negative refraction (the energy flow and the phase velocity of an electromagnetic waves propagates in opposite directions). I will show that negative refraction seems to be a quite generic phenomenon in homogeneous, isotropic systems that have a finite non zero charge density and admits an hydrodynamics description. In the second part of the seminar I will give a proposal for the 3d field theory living on the a sack of N anti-M2 branes living at the tip of a supersymmetric 8 dimensional cone. This kind of field theory is know to be dual to an explicit non supersymmetric stable supergravity solution known as the skew-whiffing Freud-Rubin solution. I will explicitly discuss the case of anti M2 branes at the tip of the real cone on S7/Zk where I will give a proposal for the field theory and I will check that the spectrum of the gauge invariant operators in the field theory reproduce the KK spectrum in supergravity.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, February 16, 2011 at 10:30

### "Thermalization of strongly coupled field theories"

Ben Craps (VUB)

Leuven - February 9, 2011

Using the AdS/CFT correspondence, we probe the scale-dependence of thermalization in strongly coupled field theories following a quench via saddlepoint calculations of 2-point functions, Wilson loops and entanglement entropy in d=2,3,4. For homogeneous initial conditions, the entanglement entropy thermalizes slowest, and sets a timescale for equilibration that saturates a causality bound. The growth rate of entanglement entropy density is nearly volume-independent for small volumes, but slows for larger volumes. In this strongly coupled setting, the UV thermalizes first.

Place: Leuven, Celestijnenlaan 200D 06.32

Time: Wednesday, February 09, 2011 at 13:00

### "Transport in holographic (super)fluids"

Piotr Surowka (VUB)

Leuven - February 9, 2011

I will present how to develop a general framework for hydrodynamics within AdS/CFT corresponence. Moreover, I will show how that approach inspired extension of known hydrodynamics to the case with triangle anomalies. Finally, I will descrpibe some recent results, how to analytically obtain two-fluids Landau-Tisza model near phase transition using fluid/gravity duality.

Place: Leuven, Celestijnenlaan 200D 06.32

Time: Wednesday, February 09, 2011 at 10:30

### "Type IIB consistent truncations and their applications to holography"

Davide Cassani (Padua University)

VUB/ULB - February 2, 2011

In the context of the gauge-gravity duality, consistent truncations have proved to be powerful solution-generating tools, their latest application being to the holographic description of condensed matter systems. In the talk, I will discuss a rich class of consistent truncations of type IIB supergravity on squashed Sasaki-Einstein manifolds, leading to N=4 or N=2 gauged supergravity in five dimensions. As examples of the several possible applications, I will present a new class of AdS5 backgrounds on the T(1,1) coset, as well as some related non-relativistic Lifshitz solutions.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, February 02, 2011 at 13:00

### "Massive Gravity"

Viatcheslav Mukhanov (Arnold Sommerfeld Center, Munich)

VUB/ULB - February 2, 2011

I will consider Higgs mechanism for graviton. It will be shown how van Dam, Veltman, Zakharov discontinuity problem is resolved and will be proved that General Relativity is restored at the scales below the Vainstein scale. The problem of nonlinear Boulware-Deser ghost will be discussed.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, February 02, 2011 at 10:30

### "SUSY gauge theory, Liouville theory, and the quantization of Hitchin moduli spaces"

Joerg Teschner (DESY)

VUB/ULB - December 15, 2010

The first part of my talk is going to be a survey of the recently discovered relations between certain SUSY gauge theories and Liouville theory, stressing in particular some consequences for the study of strong-weak coupling dualities in these gauge theories. As a step towards a better understanding of these relations we shall then discuss some relations to the Hitchin integrable system and its quantization.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, December 15, 2010 at 13:00

### "Helical Luttinger Liquids and Three Dimensional Black Holes"

Vijay Balasubramanian (University of Pennsylvania)

VUB/ULB - December 15, 2010

Cold interacting fermions in two dimensions form exactly solvable Luttinger liquids, whose characteristic scaling exponents differ from those of a conventional Fermi liquid. We use the AdS/CFT correspondence to establish an equivalence between a class of helical, strongly coupled Luttinger liquids and fermions propagating in the background of a three dimensional black hole. The microscopic Lagrangian is explicitly known and the construction is fully embeddable in string theory. The cuts in the retarded Green function that control the low-temperature behavior arise in the gravitational picture from the structure of the geometry very near the black hole horizon. The structure we study is universally present in all cold, charged liquids with a dual description in gravity.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, December 15, 2010 at 10:30

### "Superembedding approach to M-waves and Matrix model interaction with eleven dimensional supergravity"

Igor Bandos (Bilbao)

UMons - December 8, 2010

After a brief and elementary introduction to superfield methods and, particularly, to superembedding approach to supersymmetric extended objects, super-p-branes, we apply this latter to search for equations of motion for the system of multiple M0-branes (multiple M-waves or eleven dimensional massless superparticles) in an arbitrary curved 11D supergravity superspace. In such a way we obtain the covariant equations describing Matrix model interaction with an arbitrary supergravity background. Superembedding approach also allows to find the BPS conditions for the supersymmetric solutions of the multiple M-wave equations. We discuss the 1/2 supersymmetric solution modeling M2-brane (11D supermembrane) by a multiple M-wave configuration and show that the famous Nahm equations appear as a particular case of the 1/4 BPS conditions.

Place: UMons Salle 0A07, Pentagone

Time: Wednesday, December 08, 2010 at 13:00

### "Asymptotic symmetries of 3D gravity coupled to higher-spin fields"

Andrea Campoleoni (Golm)

UMons - December 8, 2010

We discuss the relation between non-linear W-algebras and the asymptotic symmetries of higher-spin gauge theories coupled to three-dimensional gravity with a negative cosmological constant. They can be described by G × G Chern-Simons theories and their asymptotic symmetries are given by two copies of a centrally extended W-algebra selected by the gauge group G. The central charge is the one identified by Brown and Henneaux in pure gravity.

Place: UMons, Salle 0A07, Pentagone

Time: Wednesday, December 08, 2010 at 10:30

### "The Penrose Inequality and the Fluid-Gravity Correspondence"

Yaron Oz (Tel-Aviv University)

Leuven - December 1, 2010

In general relativity, the Penrose inequality relates the mass and the entropy associated with a gravitational background. If the inequality is violated by some Cauchy data, it suggests a creation of a naked singularity, thus providing means to consider the cosmic censorship hypothesis. The analogous inequality in the context of fluid dynamics can provide a valuable tool in the study of finite time blowups in hydrodynamics. We derive the inequality for relativistic and non-relativistic fluid flows in general dimension and analyze the implications.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, December 01, 2010 at 13:00

### "Lifshitz Solutions of String and M-Theory "

Jerome Gauntlett (Imperial College London)

Leuven - December 1, 2010

There has been recent interest in trying to use the Anti-de-Sitter/ Conformal Field Theory correspondence to model strongly coupled condensed matter systems. One focus has been on quantum critical points that exhibit anisotropic or "Lifshitz" scaling. We discuss solutions of string and M-theory which capture such Lifshitz scaling symmetry. One construction, involving Sasaki-Einstein spaces, leads to an infinite set of examples. A second construction involves a new consistent Kaluza-Klein truncation of D=11 supergravity when reduced on the product of a four-sphere with a three-dimensional Einstein space, and is related to M5-branes wrapping special Lagrangian three-cycles.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, December 01, 2010 at 10:30

### "Moduli Stabilization in heterotic string and M-theory"

James Gray (Oxford)

Leuven - November 24, 2010

After giving an extended introduction to the subject of phenomenological compactifications of heterotic string and M-theory, I will go on to discuss the stabilization of moduli fields in this context. In particular I will describe how the complex structure moduli of Calabi-Yau threefolds can be stabilized due to the presence of gauge field expectation values in the compactified dimensions. I will then discuss how this effect can be built into a more complete stabilization scenario.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, November 24, 2010 at 13:00

### "Emergent Gauge Fields in AdS/CM"

Pedro Silva (Universitat Autonoma de Barcelona)

Leuven - November 24, 2010

Holographic superconductors have been studied so far in the absence of dynamical electromagnetic fields, namely in the limit in which they coincide with holographic superfluids. It is possible, however, to introduce dynamical gauge fields if a Neumann-type boundary condition is imposed on the AdS-boundary. In 3+1 dimensions, the dual theory is a 2+1 dimensional CFT whose spectrum contains a massless gauge field, signaling the emergence of a gauge symmetry. We study the impact of a dynamical gauge field in vortex configurations where it is known to significantly affect the energetics and phase transitions.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, November 24, 2010 at 10:30

### "Microscopic realization of the Kerr/CFT correspondence "

Monica Guica (LPTHE)

VUB/ULB - November 17, 2010

Supersymmetric M/string compactifications to five dimensions contain BPS black string solutions with magnetic graviphoton charge P and near-horizon geometries which are quotients of AdS3 × S2. The holographic duals are typically known 2D CFTs with central charges cL=cR=6P3 for large P. These same 5D compactifications also contain non-BPS but extreme Kerr-Newman black hole solutions with SU(2)L spin JL and electric graviphoton charge Q obeying Q3 ≤ JL2. It is shown that in the maximally charged limit Q3 → JL2, the near-horizon geometry coincides precisely with the right-moving temperature TR=0 limit of the black string with magnetic charge P=JL1/3. The known dual of the latter is identified as the cL=cR=6JL CFT predicted by the Kerr/CFT correspondence. For general Q3 < JL2, one has a finite-temperature quotient of a warped deformation of the magnetic string geometry. We show that at linear order away from maximality, the temperature quotient of the AdS3 factor of the black solution reproduces, via Cardy's formula, the linearly sub-maximal Kerr-Newman entropy. We also describe the CFT operator responsible for the warping of the geometry to leading order away from maximality.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, November 17, 2010 at 13:00

### "Critical overview of Loops and Foams "

Sergei Alexandrov (Université Montpellier II)

VUB/ULB - November 17, 2010

I will give a critical review (from a personal viewpoint) of the present status and recent progress of loop and spin foam approaches to quantization of four-dimensional general relativity, and raise various issues which challenge some of the methods and the results in these domains. In particular, I will argue that the present realization of the loop quantization provided by LQG is likely to be anomalous, whereas the quantization strategy employed in the most of spin foam models is inconsistent with the rules of canonical quantization. On the other hand, I will suggest modifications of these two approaches which may overcome their problems.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, November 17, 2010 at 10:30

### "Double Field Theory and the Geometry of Duality"

Chris Hull (Imperial College London)

VUB/ULB - November 10, 2010

String theory on a torus requires the introduction of dual coordinates conjugate to string winding number. For a d-torus, string theory can be formulated in terms of an infinite tower of fields depending on both the d torus coordinates and the d dual coordinates. This talk focuses on a finite subsector consisting of a metric and b-field (both d × d matrices) and a dilaton all depending on the 2d doubled torus coordinates. The double field theory is constructed and found to have a novel symmetry that reduces to diffeomorphisms and anti-symmetric tensor gauge transformations in certain circumstances. It also has manifest T-duality symmetry which provides a generalisation of the usual Buscher rules to backgrounds without isometries. The theory has a real dependence on the full doubled geometry: the dual dimensions are not auxiliary. It is concluded that the doubled geometry is physical and dynamical.

Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Rm906, Salle des Professeurs

Time: Wednesday, November 10, 2010 at 13:00

### "Generating gravity duals using G-structures "

Jerome Gaillard (Swansea University)

VUB/ULB - November 10, 2010

In order to find new supergravity solutions, one can use the geometric formalism of G-structures as a guide. Using the example of SU(3), I am going to present how one can use geometry in order to generate solutions, and and include backreacting sources. I will talk about how those new solutions relate to known ones, before finally discussing their field theory duals.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, November 10, 2010 at 10:30

### "Higher spin gauge field interactions and the beauty of Noether's procedure"

Ruben Manvelyan (Technical University of Kaiserslautern)

VUB/ULB - November 3, 2010

Using Noether's procedure we present a complete solution for the trilinear interactions of arbitrary spins s1, s2, s3 in a flat background, and discuss the possibility to enlarge this construction to higher order interactions in the gauge field. We also present an off-shell generating function for all cubic interactions of Higher Spin gauge fields. It is written in a very compact way, and turns out to have a remarkable structure.

Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Rm906, Salle des Professeurs

Time: Wednesday, November 3, 2010 at 13:00

### "Black holes in supergravity and integrability"

Wissam Chemissany (K.U.Leuven)

VUB/ULB - November 3, 2010

Stationary black holes of massless supergravity theories are described by certain geodesic curves on the target space that is obtained after dimensional reduction over time. When the target space is a symmetric coset space we make use of the group-theoretical structure to prove that the second order geodesic equations are integrable in the sense of Liouville, by explicitly constructing the correct amount of Hamiltonians in involution. This implies that the Hamilton-Jacobi formalism can be applied, which proves that all such black hole solutions, including non-extremal solutions, possess a description in terms of a (fake) superpotential. Furthermore, we improve the existing integration method by the construction of a Lax integration algorithm that integrates the second order equations in one step instead of the usual two step procedure

Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Rm906, Salle des Professeurs

Time: Wednesday, November 3, 2010 at 10:30

### "Hawking radiation from dielectric black holes"

Sergio Cacciatori (Insubria University & INFN Milano)

Leuven - October 27, 2010

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta: Hawking radiation. In 1981 Unruh has shown that in principle this phenomenon could be observed in laboratory by simulating event horizons in testable systems. I will show how analogue black and white hole horizons can be realized in suitable dielectric media. The peculiarity of such analogue black holes w.r.t. the "traditional ones" is due to dispersion, which changes the expected emission spectrum. This however can be predicted as a function of the main parameters characterizing the analogue system. I will describe how we have experimentally created such a gravitational analogue using ultrashort laser pulse filaments. Our measurements demonstrate a spontaneous emission of photons that confirms the theoretical predictions.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, October 27, 2010 at 13:00

### "Massive type IIA string theory cannot be strongly coupled"

Alessandro Tomasiello (Milano Bicocca University)

Leuven - October 27, 2010

String theory is understood today as a single entity, thanks to the dualities established in the ‘90s. An imperfection in this picture is, however, the issue of the strong coupling limit of the ‘massive’ type IIA theory. We will argue that perhaps this problem does not exist. Namely, we will show explicitly that massive type IIA string theory can never be strongly coupled in a weakly curved region of space-time. We will illustrate this general claim with two classes of massive solutions in AdS4 × CP3, with N = 1 and N = 2 supersymmetry. Both solutions are holographically dual to d = 3 Chern–Simons–matter theories. In both these massive examples, as the rank N of the gauge group is increased, the dilaton initially increases in the same way as in the corresponding massless case; before it can reach the M–theory regime, however, it enters a second regime, in which the dilaton decreases even as N increases. In the N = 2 case, we find supersymmetry–preserving gauge–invariant monopole operators whose mass is independent of N. This predicts the existence of branes which stay light even when the dilaton decreases. We will show that, on the gravity side, these states originate from D2–D0 bound states wrapping the vanishing two–cycle of a conifold singularity that develops at large N.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, October 27, 2010 at 10:30

### "Towards a Microscopic Description of Extremal Kerr using M5 branes"

Geoffrey Compère (Amsterdam)

VUB/ULB - October 20, 2010

A microscopic analysis of the extremal Kerr black hole will be initiated using a brane construction. The key observation that will be presented is the following: the magnetically charged spinning one-brane in minimal supergravity admits a decoupling limit which interpolates smoothly between the self-dual null orbifold of AdS3 × S2 and the near-horizon region of the extremal Kerr black hole times a circle. This solution will be used to find the specific deformations of the CFT dual to AdS3 × S2 which correspond to the supergravity deformation leading to the Kerr geometry.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, October 20, 2010 at 13:00

### "Some Adventures in T-duality"

Daniel Thompson (VUB)

VUB/ULB - October 20, 2010

In this talk I shall introduce myself, give a flavor of the some past research and current research interests. I will provide a survey some of my recent results concerning various aspects of T-duality including duality invariance & the Doubled Formalism, fermionic T-duality and non-abelian T-duality. To conclude I will present some directions which I hope to pursue over the coming year.

Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay

Time: Wednesday, October 20, 2010 at 10:30

### "Towards the exact spectrum of the AdS5 × S5 superstring "

Arutyunov Gleb (Utrecht)

Leuven - October 13, 2010

I discuss recent advances towards finding the exact spectrum of the AdS5 × S5 superstring based on the Thermodynamic Bethe Ansatz for the accompanying mirror model.

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, October 13, 2010 at 13:00

### "Negative refractive index from AdS/CFT "

Giuseppe Policastro (LPTENS Paris)

Leuven - October 13, 2010

I will discuss how relativistic plasmas with a gravitational dual description have unusual optical properties and in particular a negative index of refraction, a property experimentally observed in some special classes of materials. The talk is based on the paper 1006.5714

Place: Leuven, Celestijnenlaan 200D 05.11

Time: Wednesday, October 13, 2010 at 10:30

### "Relativistic Beaming in AdS/CFT "

Veronika Hubeny (Durham)

VUB/ULB - October 6, 2010

This talk is cast within the context of AdS/CFT, in particular the relation between the radiation produced by accelerating quark at the boundary, and the motion of a fundamental string in the bulk AdS spacetime. We discuss how a string source deep in bulk of AdS can nevertheless induce highly localized energy density in the boundary CFT.

Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Rm906, Salle des Professeurs

Time: Wednesday, October 6, 2010 at 13:00

### "Nonabelian (2,0) Tensor Multiplets and 3-algebras"

Costis Papageorgakis (King's College London)

VUB/ULB - October 6, 2010

Using 3-algebras we obtain a nonabelian system of equations that furnish a representation of the (2,0)-supersymmetric tensor multiplet. The on-shell conditions are quite restrictive so that the system can be reduced to five-dimensional super-Yang-Mills theory along with six-dimensional abelian (2,0) tensor multiplets. We discuss possible applications to D4-branes and M5-branes.

Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Rm906, Salle des Professeurs

Time: Wednesday, October 6, 2010 at 10:30