# Joint seminars academic year: 2013-2014

### Dimitris Giataganas (Athens, Greece & Witwatersrand University, South Africa)

Wednesday, May 28, 2014 - 13:00

### Non-BPS walls of marginal stability

Stefanos Katmadas (Milan Bicocca, Italy)

Wednesday, May 21, 2014 - 13:00

UMONS VESALE25 building 7

We present recent progress on non-BPS multi-black hole systems in ungauged N=2 supergravity coupled to vector multiplets. Focusing on extremal solutions and allowing for arbitrary non-BPS charges to be carried by each black hole, we discuss the structure of the resulting solutions. We furthermore consider the binding energy of the composites and show the existence of walls of marginal stability for generic choices of charges. Time permitting, a brief discussion of more general, non-extremal systems will be given.

### Locally USp(8) invariant IIB Supergravity and E6(6) covariance

Bernard de Wit (NIHEF, Amsterdam & Utrecht U.)

Wednesday, May 21, 2014 - 10:30

UMONS VESALE25 building 7

Local USp(8) invariance and E6(6) covariance of IIB supergravity is analyzed in a form where the embedding of the five-dimensional maximal supergravity is made manifest. The ten-dimensional theory yields all the 27 one-form fields and 22 of the 27 two- form fields that are required by the vector-tensor hierarchy of the five-dimensional theory. The missing 5 two-form fields emerge from the elusive ‘dual graviton’. The implications are discussed as well as a partial proof of the consistency of the truncation of IIB supergravity on the five-sphere

### Solvay Workshop "Fast is Beautiful"

Thursday, May 15, 2014 - 00:00

Solvay Workshop "Fast is Beautiful"

Wednesday, May 14, 2014 - 00:00

ULB Solvay Room

http://www.solvayinstitutes.be/index.php?pageid=2&ssid=3

### Effective world-volume theory of charged black branes

Niels Obers (NBI Copenhagen, Denmark)

Wednesday, April 30, 2014 - 13:00

KUL 200E 01.207

In the long-wave length regime, charged black branes behave like any other type of continuous media, with their dynamics governed by an effective theory, described by the blackfold approach. First an introduction to this development will be given, and next we turn to more recent insights. In particular, I will show that asymptotically charged black branes of supergravity have both elastic and hydrodynamic properties, which can be obtained by considering extrinsic and intrinsic perturbations respectively. As a consequence, one can determine new (first order) response coeffi cients of large classes of charged black branes, including the Young modulus and piezo electric moduli along with hydrodynamic transport coe fficients. I will also briefly discuss the generalization of the blackfold approach to branes in arbitrary backgrounds, including fluxes and comment on possible applications. Finally, I will outline relations and possible applications to the AdS fluid/gravity correspondence and the use of blackfolds as thermal probe branes.

### BPS Quivers and N=2 superconformal theories

Simone Giacomelli (ULB)

Wednesday, April 30, 2014 - 10:30

KUL 200E 01.207

The BPS spectrum of a large class of N=2 theories can be encoded in an oriented graph called BPS quiver. In this talk I will review the BPS quiver technique and the 4d/2d correspondence introduced by Cecotti, Neitzke and Vafa. In the second part of the talk, based on a work in collaboration with Sergio Cecotti and Michele Del Zotto, I will explain how the BPS quiver technology can be used to study a new class of N=2 superconformal models construceted via Type IIB geometric engineering. The computation of various quantities of interest such as scaling dimensions of chiral operators and central charges can be translated via the 4d/2d correspondence into two-dimensional problems.

### Inflating the Bicep(2).

Diego Chialva (UMONS)

Wednesday, April 23, 2014 - 14:00

ULB Solvay Room

The results of the Bicep2 experiment have caused a stir in the physics community. Various claims have been resonating (discovery of inflationary scale, detection of quantum gravity, and others).

But what does Bicep2 really measure? How strong is this result? Is it in tension with other results? And what are the elements that link it to inflation? Does it hint at something else, even? In this talk I will try to answer these questions and illustrate in a quantitative way what is the link between the observations and the underlying theory. I will also discuss what are the new perspectives opened concerning the theory, in particular contrasting them with the views that were predominant in the field after Planck results.

The format of the talk will give a big role to questions from the audience (you are invited not to refrain from asking!), aiming at filling gaps in the different kinds of notions and expertise involved.

### Pre-Inflationary Clues from String Theory?

Augusto Sagnotti (University of Pisa, Italy)

Wednesday, April 23, 2014 - 10:30

ULB Solvay Room

Brane supersymmetry breaking'' occurs in String Theory when the only available combinations of D--branes and orientifolds are not mutually BPS and yet do not introduce tree--level tachyon instabilities. It is characterized by the emergence of a steep exponential potential, and thus by the absence of maximally symmetric vacua. The corresponding low--energy supergravity admits intriguing spatially--flat cosmological solutions where a scalar field is forced to climb up toward the steep potential after an initial singularity, and additional milder terms can inject an inflationary phase during the ensuing descent. We show that, in the resulting power spectra of scalar perturbations, an infrared suppression is typically followed by a pre--inflationary peak that reflects the end of the climbing phase and can lie well apart from the approximately scale invariant profile. A first look at WMAP9 raw data shows that, while the chi-squared fits for the low--l CMB angular power spectrum are clearly compatible with an almost scale invariant behavior, they display nonetheless an eye--catching preference for this type of setting within a perturbative string regime.

### Solvay Workshop "holography for black holes"

Friday, April 18, 2014 - 11:30

### Solvay Workshop "holography for black holes"

Thursday, April 17, 2014 - 11:30

### Solvay Workshop "holography for black holes"

Wednesday, April 16, 2014 - 11:30

### Solvay Workshop "holography for black holes"

Tuesday, April 15, 2014 - 11:30

### Solvay Workshop "holography for black holes"

Monday, April 14, 2014 - 00:00

http://www.solvayinstitutes.be/events/holography_for_black_holes/hologra...

### The geometry of supersymmetric partition functions

Guido Festuccia (NBI Copenhagen, Denmark)

Wednesday, April 9, 2014 - 13:00

ULB Solvay Room

I will consider supersymmetric field theories on compact manifolds M and obtain constraints on the dependence of their partition functions ZM on the geometry of M. For N=1 theories with a U(1) R symmetry in four dimensions, M must be a complex manifold with a Hermitian metric. In this case ZM is independent of the metric and depends holomorphically on the complex structure moduli. In examples where ZM has been calculated explicitly, these results explain many of its observed properties.

I will also consider three-dimensional N=2 theories with a U(1) R symmetry, where the necessary geometric structure on M is a transversely holomorphic foliation (THF) with a transversely Hermitian metric. Again, ZM is independent of the metric and depends holomorphi- cally on the moduli of the THF.

### Boundary dynamics of 3D asymptotically flat gravity

Hernan Gonzales (ULB)

Wednesday, April 9, 2014 - 10:30

ULB Solvay Room

We construct a two-dimensional action principle invariant under BMS3 group. Such a theory is obtained through a reduction of Chern-Simons action. This procedure is carried out by imposing a set of boundary conditions obtained from asymptotically ﬂat spacetimes in three dimensions. When implementing part of this set, we obtain an analog of chiral WZW model based on three dimensional Poincaré algebra. The remaining part of the boundary conditions imposes constraints on the conserved currents of the model, which allows to further reduce the action principle to a BMS3 Liouville invariant theory. Some extensions of this result to include higher spin fields will be also discussed.

### Lifshitz & hyperscaling violating holography with arbitrary critical exponent z>1

Ioannis Papadimitriou (Madrid, IFT)

Wednesday, April 2, 2014 - 13:00

VUB D.3.15

I am going to discuss a very general algorithm for constructing the holographic dictionary in both asymptotically AdS and non-AdS backgrounds. After reviewing this technique in the context of relativistic theories, I will present work in progress on the application of this method to a very general class of theories that admit Lifshitz and hyperscaling violating Lifshitz backgrounds.

### Strings in compact cosmological spaces

Oleg Evnin (Chulalongkorn U. & Intl. Solvay Inst., Brussels & Vrije U. Brussel)

Wednesday, April 2, 2014 - 10:30

VUB D.3.15

Formulating perturbative string theory in a spatially compact universe proves difficult, essentially on account of significant cosmological backreaction induced on the background space-time by the presence of even a single string quantum.

Mathematically, the problem manifests as infrared divergences in traditionally defined string amplitudes. I shall review a recently proposed formalism addressing these issues.

### Scanning Tunneling Macroscopy, Black Holes, and AdS/CFT Bulk Locality

Vladimir Rosenhaus (Berkeley)

Wednesday, March 26, 2014 - 13:00

KUL 200B 00.05

We establish resolution bounds on reconstructing a bulk field from boundary data on a timelike hypersurface. If the bulk only supports propagating modes, reconstruction is complete. If the bulk supports evanescent modes, local reconstruction is not achievable. For a Minkowski bulk, one can reconstruct a spatially coarse-grained bulk field, but only out to a depth set by the coarse-graining scale. For an asymptotically AdS bulk, reconstruction is limited to a spatial proper distance coarse-graining set by the AdS scale. An AdS black hole admits evanescent modes. We study the resolution bound in the large AdS black hole background and provide a dual CFT interpretation. Our results demonstrate that if there is a black hole of any size in the bulk, boundary data in terms of local CFT operators becomes insufficient for probing the bulk on sub-AdS scales.

### A New Class of QFTs: from D-branes to the Geometry of Scattering Amplitudes

Sebastian Franco (Durham)

Wednesday, March 26, 2014 - 10:30

KUL 200B 00.05

Over the last decade, we have witnessed remarkable progress in our understanding of Quantum Field Theories. New insights have emerged from a multitude of fronts, ranging from the Gauge/Gravity Correspondence to Integrability. In this seminar I will discuss Bipartite Field Theories (BFTs), a new class of QFTs embodying many of these new approaches. BFTs are 4d, N=1 quiver gauge theories with Lagrangians defined by bipartite graphs on Riemann surfaces. Remarkably, they underlie a wide spectrum of interesting physical systems, including: D-branes probing Calabi-Yau manifolds, their mirror configurations, integrable systems in (0+1) dimensions and on-shell diagrams in N=4 SYM. I will introduce new techniques for studying these gauge theories. I will explain how their dynamics is captured graphically and the interesting emergence of concepts such as Calabi-Yau manifolds, the Grassmannian and cluster algebras in the classification of IR fixed points. Finally, I will introduce a new framework for analyzing general systems of D3 and D7-branes over toric Calabi-Yau 3-folds. These ideas can be exploited for embedding BFTs in String Theory but have a much wider range of applicability.

### A Holographic Model of the Kondo Effect

Andy O'Bannon (Oxford)

Wednesday, March 19, 2014 - 13:00

ULB Solvay Room

The Kondo effect occurs in metals doped with magnetic impurities: in the ground state the electrons form a screening cloud around each impurity, leading to dramatic changes in the thermodynamic and transport properties of the metal. Although the single-impurity Kondo effect is considered a solved problem, many questions remain, especially about the fate of the Kondo effect in the presence of multiple impurities. In particular, for a sufficiently dense concentration of impurities, a competition between the Kondo effect and inter-impurity interactions can lead to quantum criticality and non-Fermi liquid behavior, which remains poorly understood. In this talk I will present a model of the single-impurity Kondo effect based on holography, also known as gauge-gravity duality or the AdS/CFT correspondence, which may serve as a foundation for a new approach to the multiple-impurity system.

### Higher Spin Lifshitz Holography

Michael Gary (Vienna Tech)

Wednesday, March 19, 2014 - 10:30

ULB Solvay Room

We study three-dimensional spin-3 higher-spin gauge theory with z = 2 Lifshitz ground state, which carries nontrivial spin-2 and spin-3 charges. After providing consistent boundary conditions and determining the associated asymptotic symmetry algebra, we consider the possible geometric interpretation of the theory in light of the higher spin gauge invariance and remark on the implications of the asymptotic symmetry analysis.

### Brane deformations in Supergravity

Vasilis Niarchos (U. Crete, Greece)

Wednesday, March 12, 2014 - 13:00

ULB Solvay Room

I will present recent work on the physics of long-wavelength supersymmetric deformations of brane solutions in supergravity. We will see how familiar concepts from D-brane theory, like the Dirac-Born-Infeld action and the kappa-symmetry condition, arise directly from the supergravity equations and will discuss their implications on the SUGRA/DBI correspondence. As a concrete example, we will consider the case of M5 branes in eleven-dimensional supergravity.

### Pure states and black hole complementarity

Larus Thorlacius (Nordita & Iceland U.)

Wednesday, March 12, 2014 - 10:30

ULB Solvay Room

Hawking's black hole information paradox arises when the formation and subsequent evaporation of a black hole is examined in the context of quantum theory. In a gravity theory with a gauge theory dual, the paradox must be resolved in favor of unitary evolution. The challenge is then to implement unitarity on the gravity side and a key issue, which is at the center of the recent debate on firewalls, is whether this requires giving up the equivalence principle. For a black hole formed in a generic pure quantum state, we argue that a typical infalling observer will see no drama on their way to the stretched horizon and a proposal is made for an approximate interior effective field theory description where this conclusion holds until the observer approaches the black hole singularity.

### Holographic Thermal Helicity

Tatsuo Azeyanagi (Harvard)

Wednesday, March 5, 2014 - 13:00

ULB Solvay Room

In this talk, we discuss a thermal observable called the thermal helicity of CFT with anomalies in the context of AdS/CFT. We consider large charged rotating AdS black holes in the Einstein-Maxwell-Chern-Simons theory with a negative cosmological constant using fluid/gravity expansion. We then compute the anomaly-induced current and stress tensor of the dual CFT in leading order of the fluid/gravity derivative expansion to show their agreement with the field theoretical replacement rule for the thermal helicity. Such replacement rule is reflected in the bulk by new replacement rules obeyed by the Hall currents around the black hole.

### Conformal Invariance in Momentum Space

Adam Bzowski (KULeuven)

Wednesday, March 5, 2014 - 10:30

ULB Solvay Room

Based on a position space analysis it can be shown that correlation functions in conformal field theories are highly constrained by symmetries. In the talk I will concentrate on the analysis carried out in momentum space. I will present a novel approach, which allows to solve conformal Ward identities directly in momentum space. Furthermore, I will show that all 3-point functions in a CFT involving stress energy tensor, conserved currents and various scalar operators can be easily expressed in terms of (almost) elementary functions.

### Microstate geometries and their (double) CFT description

Rodolfo Russo (Queen Mary, UK)

Wednesday, February 26, 2014 - 13:00

KUL 200E 01.207

As is well known, the extremal 5D Reissner-Nordstrom black hole can be embedded in type IIB string theory by using the D-brane construction of Strominger and Vafa. Over the past years, several 1/8-BPS supergravity solutions have been constructed that can represent microstates for this black hole. From the D-brane construction, it is expected that each microstate solution should have two different CFT descriptions: one related to the near-horizon limit following from the AdS/CFT correspondence and another related to the asymptotic flat region in terms of the world-sheet CFT describing the D-branes. I will describe this double connection and present some new microstate geometries that should have a clear interpretation in both of these limits.

### Entanglement entropy of massive flavor fields

Giuseppe Policastro (ENS Paris)

Wednesday, February 26, 2014 - 10:30

KUL 200E 01.207

We discuss the corrections to the entanglement entropy due to the introduction of massive flavor fields in a conformal field theory described holographically. The mass dependence allows to identify some universal contributions that can be compared to the perturbative results. We also discuss some alternative proposals that do not use the backreaction of the fields on the geometry.

### Higher spin theory in 3D flat space

Jan Rosseel (Vienna Tech)

Wednesday, February 19, 2014 - 13:00

ULB Solvay Room

In this talk, I will consider higher spin gravity theories in three-dimensional asymptotically flat space-times. I will consider the example of a spin-3 gravity theory and will show that consistent boundary conditions can be imposed that are compatible with asymptotically flat space-time. I will discuss the asymptotic symmetry algebra, that can be interpreted as the symmetry algebra of a putative field theory dual. Prospects for unitarity of this dual field theory will be discussed.

### Flat Space Holography: Cosmological Entropy, Chiral Gravity and Phase Transitions

Stephane Detournay (ULB)

Wednesday, February 19, 2014 - 10:30

ULB Solvay Room

This talk will report on progress in defining a holographic dictionary for gravity theories in flat space.

The symmetry algebra of asymptotically flat spacetimes at null infinity consists in the so-called BMS algebra. In 2+1 dimensions, it plays the role of the two dimensional conformal algebra for AdS_3 gravity. Interestingly, the corresponding phase space contains solutions that can be interpreted as cosmological spacetimes. In particular, they possess a non-trivial Bekenstein-Hawking entropy. We show that the latter can be reproduced by an asymptotic counting of states in the putative dual theory, by deriving an analog of the Cardy formula for BMS_3-invariant theories.

We then describe a limit in which the symmetry algebra reduces to a chiral copy of a Virasoro algebra, and conjecture that the dual theory can be identied with a chiral CFT. We finally discuss a flat-space analog of the Hawking-Page phase transition.

### Chiral Liouville gravity and AdS3

Geoffrey Compere (ULB)

Wednesday, February 12, 2014 - 13:00

ULB Solvay Room

I will present an example of two-dimensional quantum field theory with chiral conformal symmetry but not complete conformal symmetry. It will be derived from two-dimensional Polyakov gravity and from Einstein gravity in three dimensions in AdS3 with new chiral boundary conditions.

### Higher spins, holography and strings

Per Sundell (Andres Belle Natl. U.)

Wednesday, February 12, 2014 - 10:30

ULB Solvay Room

We review higher spin gravities in the context of holography and string theory.

### Exceptional Form of D=11 Supergravity

Henning Samtleben (Lyon)

Wednesday, February 5, 2014 - 13:00

KUL 200E 01.207

Eleven-dimensional supergravity upon dimensional reduction reveals large exceptional symmetries, in accordance with the U-duality groups of M-theory. Their higher-dimensional geometric origin has remained a mystery. I report on recent work showing that D=11 supergravity upon proper extension to an `exceptional space-time' becomes fully covariant under the exceptional groups E_{n(n)}. This covariant form likewise comprises type IIB supergravity.

### Counterterms in gravity and N=8 Supergravity!

Lars Brink (Chalmers U.)

Wednesday, February 5, 2014 - 10:30

KUL 200E 01.207

In this talk I will describe how to find counterterms in gravity theories using the light-cone formulation. In my formulation all unphysical degrees of freedom are solved for. Even so I will show that one needs a kind of remaining gauge invariance to select the correct terms in the Hamiltonian. It is not enough to use just Poincaré invariance.

### Universe or Multiverse?

Van Riet - Hertog

Wednesday, December 11, 2013 - 13:00

KUL 200E 01.207

We discuss a number of exciting open problems at the interface of string theory and cosmology. These include questions surrounding the vacuum structure of string theory as well as the problem how to relate that structure to predictions for cosmological observations.

This talk will be somewhat less technical than a usual HEP seminar.

### Aspects of entanglement: entropies, negativity and causal holographic information

Erik Tonni (INFN, TRIESTE & SISSA, Trieste)

Wednesday, December 11, 2013 - 10:30

KUL 200E 01.207

Entanglement of quantum states and its measures play an important role in many areas of theoretical physics. Holographic techniques have been also largely employed to understand them.

The entanglement entropy is a good measure for pure states, while the negativity allows us to quantify entanglement for mixed states.

After an introductory discussion, the computation of the Renyi entropies for a generic number of disjoint intervals in CFT is discussed and analytic results are provided for the free compactified boson and the Ising model. A method to compute negativity in QFT through the replica trick will be described. Within the class of theories with a holographic dual, besides the holographic entanglement entropy, a natural quantity to introduce is the causal holographic information. Its definition and properties will be briefly discussed.

### Cubic interactions and Symmetries of Higher-spin field theories

Euhiun Joung (Pisa)

Wednesday, December 4, 2013 - 13:00

VUB D.3.15

The deformations of higher-spin symmetries induced by cubic interactions of symmetric massless bosonic fields will be analyzed within the metric-like formalism. In particular, I will identify a class of couplings which leave the gauge algebra Abelian but deform one (out of three) gauge transformation, and another class of couplings which deform all three gauge transformations in (A)dS but only two in the flat-space limit. The former class is related to higher-spin algebra multiplets (representations of the global algebra). The latter class is what makes (A)dS a distinguished background for higher-spin interactions and includes in particular the gravitational interactions of higher-spin fields, retrospectively accounting for the Fradkin-Vasiliev solution to the Aragone-Deser problem. I will also discuss the restriction of gauge symmetries to global symmetries (higher-spin algebra) and some aspects of higher-spin algebras.

### A simple holographic model of momentum relaxation

Tomas Andrade (Durham)

Wednesday, December 4, 2013 - 10:30

VUB D.3.14

We consider a holographic model consisting of Einstein-Maxwell theory in (d+1) bulk spacetime dimensions with (d-1) massless scalar fields. Momentum relaxation is realised simply through spatially dependent sources for operators dual to the neutral scalars, which can be engineered so that the bulk stress tensor and resulting black brane geometry are homogeneous and isotropic. We analytically calculate the DC conductivity, which is finite. In the d=3 case, both the black hole geometry and shear-mode current-current correlators are those of a sector of massive gravity. The talk will be based on arXiv:1311.5157.

### Flavour Physics with Dirac gauginos and “how to fake a gluino”

Pantelis Tziveloglou (VUB)

Wednesday, November 27, 2013 - 13:00

KUL 200E 01.207

LHC8 raised doubts on using naturalness as a guide in our quest for physics beyond the Standard Model. In MSSM fine tuning enters through the Higgs mass and in non-minimal extensions through the negative superpartner searches. One non-minimal theory with a less severe missing superpartner problem, is MSSM with Dirac gauginos. Dirac gauginos are also known to lead to much milder flavour violation bounds. We quantify bounds in well motivated flavour models and find out that this is true but only for a very restricted class of flavour patterns. Also, in investigating Dirac gaugino models, we identified a new way of suppressing quark - “gluino” couplings with novel phenomenological features.

### Integrabilty in (super-)gravity

Axel Kleinschmidt (Potsdam, Max Planck Inst.)

Wednesday, November 27, 2013 - 10:30

KUL 200E 01.207

I will review the known integrable structures of (super-)gravity in the presence of a sufficient number of Killing vectors and how they can be used to generate new solutions. The associated inverse scattering techniques have been widely applied to four-dimensional Einstein gravity, starting with the work of Belinski and Zakharov, but their generalisation to other gravity systems poses some problems. These can be partly overcome by using the underlying group theory.

### On \alpha' corrections in F-theory.

Raffaele Savelli (IPhT, Saclay)

Wednesday, November 13, 2013 - 13:00

ULB Solvay Room

As opposed to the string coupling, F-theory has a perturbative formulation in terms of the string length. Computing \alpha' corrections to the F-theory effective physics is a challenging task and is of great relevance in string phenomenology. In this talk, I will present a modest progress in this program. I will first focus on F-theory compactified on K3xK3 and discuss the exact Kaehler potential in the \alpha' perturbation theory for the vector multiplets of the ensuing 4d, N=2 effective theory. Then I will turn to general 4d, N=1 F-theory compactifications. Using the M/F-theory duality I will present the features of a novel string correction to both the internal volume and the N=1 Kaehler coordinates.

The talk is based on the following papers: arXiv:1212.4831 and arXiv:1303.3317.

### Zwei-Dreibein Gravity: A two-frame field solution for unitary massive gravity in AdS3

Wout Merbis (Groningen)

Wednesday, November 13, 2013 - 10:30

ULB Solvay Room

Abstract: We discuss a generally-covariant and parity even two-frame field or zwei-dreibein model for massive gravity in three dimensions. It unifies previous theories of massive gravity and extends them, in the context of the AdS/CFT correspondence, to allow for positive central charge consistent with bulk unitarity.

### Solvay Workshop (no joint Hep-Th seminar)

Wednesday, November 6, 2013 - 15:30

Please see the webpage:

http://www.solvayinstitutes.be/events/ExploringHigherEnergy2013/ExploringHigherEnergy2013.html

for all the information.

### Nekrasov backgrounds from String Amplitudes

Ioannis Florakis (Munich MPI)

Wednesday, October 30, 2013 - 13:00

ULB Solvay Room

I will present a new class of N=2 amplitudes in string theory, generalizing the well-known F-terms which compute the topological string theory partition function. These generalized F-terms, in addition to the standard anti-self-dual graviphoton background, involve additional insertions of self-dual vertices. These can be identified using the non-trivial constraint that the correct N = 2 gauge theory partition function be recovered in the field theory limit, both perturbatively and non-perturbatively. The structure of the amplitudes opens up the possibility of expressing them as correlators in a topological string theory, hence leading to a worldsheet definition of the refined topological string.

### Newton-Cartan Geometry and Boundary Stress-Energy Tensor for Lifshitz Holography

Jelle Hartong (NBI, Copenhagen)

Wednesday, October 30, 2013 - 10:30

ULB Solvay Room

In this talk I will motivate the study of holography for non-AdS space-times such as Lifshitz and hyperscaling violating Lifshitz space-times. The dual field theories have a critical exponent different from unity. I will show that the boundary geometry is described by Newton-Cartan geometry with torsion and I will discuss the definition of the boundary stress-energy tensor. The model that is used can be embedded in type IIB supergravity and forms a well-behaved low energy limit of type

IIB string theory. I will discuss the definition and properties of the sources, and derive the Ward identities for the associated one-point functions. It turns out that in this model the IR of the Lifshitz geometry admits two different UV completions: 1). a theory with critical exponent z=2 and 2). a hyperscaling violating relativistic theory. Depending on time I will furthermore discuss the Lifshitz scale anomaly which takes the form of a Horava-Lifshitz action even though it is constructed in a Newton-Cartan setting, the UV/IR structure of other models admitting z=2 Lifshitz geometries, and applications.

### Wilson lines in higher spin gravity

Alejandra Castro (Amsterdam)

Wednesday, October 23, 2013 - 13:00

KUL 200E 01.207

In this talk I will review the interpretation of Wilson line operators in the context of higher spin gravity in 2+1 dim and holography. I will show how a Wilson line encapsulates the thermodynamics of black holes. Furthermore it provides an elegant description of massive particles. This opens a new window of observables which will allow us to probe the true geometrical nature of higher spin gravity.

### Quantum black holes from Yang-Mills

Toby Wiseman (Imperial)

Wednesday, October 23, 2013 - 10:30

KUL 200E 01.207

Gauge/string duality arguably provides our best framework for computing quantum properties of gravity and black holes from first principles. In the simplest instances it reformulates the problem of understanding a quantum gravity black hole in terms of understanding certain (rather special) gauge theories at finite temperature. I will review this surprising and powerful duality, and then discuss some recent attempts to understand how black hole behaviour emerges from these gauge theories.

### Collisions in AdS and the thermalisation of heavy-ion collisions

Wilke van der Schee (Utrecht)

Wednesday, October 16, 2013 - 13:00

VUB D.2.13

The motivation of this seminar is to understand the thermalisation of heavy ion collisions using AdS/CFT. For this I will present two models, the first being a somewhat simplistic boost-invariant radially expanding approach. The simplicity, however, allowed us to solve the model all the way till the final particle spectra, with an interesting comparison with experimental data.

On the more theoretical side we simulated colliding planar gravitational shock waves. This gives rise to rich and interesting dynamics; wide shocks come to a full stop and expand hydrodynamically, as was previously found by Chesler and Yaffe. High energy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms in the middle, within a proper time 1/T, with T the local temperature at that time.

In the end I will discuss recent results where we studied the influence of microscopic structure in the longitudinal direction. This has implications for both fluctuations in nucleus-nucleus collisions, and for recent proton-lead collisions at at LHC.

### Mighty Moonshine Mysteries

Daniel Persson (Chalmers)

Wednesday, October 16, 2013 - 10:30

VUB D.2.13

In mathematics and physics the word ‘Moonshine’ represents surprising and deep connections between a priori unrelated fields, such as number theory, representation theory and quantum field theory. The most famous example is Monstrous Moonshine which relates Fourier coefficients of modular forms with representations of the largest finite sporadic group, known as the Monster group. Recently, a new moonshine phenomenon was discovered, which connects the largest Mathieu group M24 with superconformal field theories on K3-surfaces. In this talk I will describe recent progress in our understanding of this 'Mathieu Moonshine', and in particular present the M24-analogue of Norton's Generalised (or 'Mighty') Monstrous Moonshine.

### Wald Entropy Current and Fluid Dynamics in the presence of Gravitational Anomaly.

Shira Chapman (Tel Aviv)

Wednesday, October 9, 2013 - 13:00

VUB D.2.13

We propose, in the framework of the fluid/gravity correspondence, a definition for a local horizon entropy current for higher-curvature gravitational theories.

As an example, we consider five-dimensional Einstein-Maxwell theory with a pure gauge and mixed gauge-gravitational Chern-Simons term.

In this theory, we construct the entropy current on a charged black-brane background, and show that it has a non-negative divergence.

Furthermore, we prove a complete correspondence between the charged black-brane horizon’s dynamics and the hydrodynamics of an anomalous field theory fluid.

Our proposed entropy current is found to coincide with the entropy current of the fluid.

### Mini-Superspace Quantum Supergravity and its Hidden Hyperbolic Kac-Moody Structures

Philippe Spindel (UMons)

Wednesday, October 9, 2013 - 10:30

VUB D.2.13

Several aspects of the quantum dynamics of a supersymmetric ``squashed three-sphere" by dimensionally reducing (to one timelike dimension) the action of $D=4$ simple supergravity for an $SO(3)$-homogeneous (Bianchi IX) cosmological model will be discussed. One finds that the quantum Hamiltonian is built from operators that generate a 64-dimensional representation of the (infinite-dimensional) maximally compact sub-algebra of the rank-3 hyperbolic Kac-Moody algebra $AE_3$. Some exponentials of these operators generate a spinorial extension of the Weyl group of $AE_3$ which describe (in the small wavelength limit) the chaotic quantum evolution of the universe near the cosmological singularity.

ref.: [arXiv : 1304.6381, Class. Quantum Grav. 30 (2013) 162001]