Theoretical Particle Physics

Joint seminars academic year: 2012-2013

Towards the real time dynamics of periodically driven holographic supercondutor

Hongbao Zhang (VUB)
Wednesday, May 15, 2013 - 13:00
Leuven 200E 01.207

In this talk, I shall report our most recent work arXiv:1305.1600, which is supposed to be a first step towards holographic investigation of the real time dynamics of periodically driven systems at strong coupling. After a quick motivation for AdS/CFT in the dynamical setting, I will show our numerical result for the real time dynamics of holographic superconductor driven by an alternating electric field. In particular, I will demonstrate the late time dynamical phase diagram for the large driving frequency, which is separated into three distinctive behaviors, namely under damped to the superconducting phase, over damped to the superconducting and normal phase, can be well understood by the low lying spectrum of quasi-normal modes in the time averaged approximation, reminiscent of the effective field theory perspective. If time permits, I would also like to advocate a new sort of local correspondence between the bulk and boundary for the entropy production by the conserved current, which was first proposed in arXiv:1204.2029.

 

A magic square from Yang-Mills squared

Leron Borsten (Imperial)
Wednesday, May 15, 2013 - 10:30
Leuven 200E 01.207

The octonions occupy a privileged position as the largest of the division algebras A (reals R, complexes C, quaternions H  and octonions O) and provide an intuitive basis for the exceptional Lie groups. Efforts to understand the exceptional groups geometrically in terms of octonions resulted in the Freudenthal-Rozenfeld-Tits magic square; a symmetric four-by-four (A1, A2) array of semi-simple Lie algebras. The octonionic row (A1= O, A2 = R, C, H, O) is exceptional: F4, E6, E7, E8.   In this presentation we will begin with an elementary introduction to division algebras and magic squares.  Then we will give a R, C, H, O  description of D = 3 Yang-Mills with N = 1, 2, 4, 8. Tensoring left and right Yang-Mills multiplets yields a magic square RR, CR, CC, HR, HC, HH, OR, OC, OH, OO  description of D = 3 supergravity with N = 2, 3, 4, 5, 6, 8, 9, 10, 12, 16. For N> 8 the multiplets are those of pure supergravity, while for N<9 they are coupled to matter. In both cases the field content is such that the U-dualities exactly match the magic square.

 

Holographic study of magnetically induced QCD effects

Nele Callebaut (Ugent & VUB)
Wednesday, May 8, 2013 - 10:30
Solvay Room

In the presence of strong magnetic fields the QCD vacuum may become unstable towards condensation of charged rho mesons, forming a superconducting state. I will talk about our investigation of this possible instability in a well-known holographic QCD model called the Sakai-Sugimoto model. Rho meson condensation does occur in this model at very high values of the magnetic field, possibly present during the cosmological electroweak phase transition or in heavy ion collisions at the LHC. Using the same model in the deconfined phase, we also investigated the Sakai-Sugimoto prediction for a possible magnetically induced split between chiral restoration and deconfinement temperature.

 

(Entanglement) Entropy in three-dimensional higher spin theories

Juan Jottar (Amsterdam)
Wednesday, May 8, 2013 - 13:00
Solvay Room

A holographic correspondence has been recently developed between higher spin theories in AdS_3 and (1+1)-dimensional CFTs with extended symmetries. In this framework, black hole solutions in the bulk theory are dual to thermal equilibrium states with non-trivial higher spin charges and chemical potentials. We discuss the calculation of the higher spin black hole entropy from an appropriate Euclidean variational principle, and provide a generalization of the Cardy entropy formula for these setups. Additionally, we present a proposal to compute entanglement entropy in the dual CFTs via holography, thus extending the Ryu-Takayanagi prescription to higher spin theories in AdS_3.

 

A holographic vieuw of the very early universe

Kostas Skenderis (Southampton, UK)
Wednesday, April 24, 2013 - 10:30
Leuven 200E 01.207

In this talk I will give an overview of holographic cosmology. I will first discuss standard inflation, show that it is holographic and discuss the new insights that come from this.  I will then present new holographic models that describe a universe that that was non-geometric at early times and describe the phenomenology and the observational signatures of these models.

 

Dualities near the Horizon

Alessio Marrani (KULeuven)
Wednesday, April 24, 2013 - 13:00
Leuven

In 4-dimensional supergravity theories, covariant under symplectic electric-magnetic duality rotations, a significant role is played by the symplectic matrix M, related to the coupling of scalars to vector field-strengths. After a general introduction on some aspects of extended supergravity theories, their duality groups "of type E7" and the corresponding notion of "Freudenthal duality", several properties of the matrix M will be discussed, in relation to the attractor mechanism of extremal (asymptotically flat) black holes. A universal expression of the symplectic vector of field strengths in terms of the dyonic black hole charge vector is discussed, in the near-horizon Bertotti-Robinson geometry. Furthermore, the Hessian of the black hole entropy will be related to the pseudo-Euclidean metric of the corresponding duality orbit supporting the black hole solution.

 

Three-point functions: SFT, integrability, and perturbative calculations.

Andrew Zayakin (Santiago de Compostela U. & Moscow, ITEP)
Wednesday, April 17, 2013 - 13:00
Solvay Room

I discuss several recent efforts in relating string field theory calculations of BMN BMN BMN and BMN BMN BPS correlation functions to direct perturbative calculations and integrability-assisted methods. I review the next-to-leading order agreement between strings and perturbation theory in the SO(6) sector, a conjectured extension of the integrability techniques by Escobedo, Gromov, Sever, Vieira from the SU(2) to the full SO(6) sector and agreement with SFT and PT in it at the leading order; finally, I discuss the issue of equating exactly extremal and non-extremal correlators at NLO in the integrability-assisted calculation.

 

Conification of Kahler and hyper-Kahler manifolds

Vincent Cortes (Hamburg)
Wednesday, April 17, 2013 - 10:30
Brussels, Solvay Room

I will show how to construct a conical K\"ahler manifold $\hat{M}$ of (real) dimension $2n+2$ out of a K\"ahler manifold $M$ of dimension $2n$ with a Hamiltonian Killing vector field. The manifold $\hat{M}$ is locally a cone over a Sasaki manifold, which in turn fibers over a K\"ahler manifold $\bar{M}$. The correspondence between $M$ and $\bar{M}$ is a new duality between K\"ahler manifolds of the same dimension. By a similar construction (generalizing results of Haydys), I will relate certain pseudo-hyper-K\"ahler manifolds to quaternionic K\"ahler manifolds of the same dimension. Applying the construction to the manifolds in the image of the rigid c-map we obtain the Ferrara-Sabharwal metric, as well as its one-loop quantum deformation. A similar result was obtained by Alexandrov, Persson and Pioline using twistor methods. The talk is based on arXiv:1205.2964 (math.DG) and work in progress.

 

On Defect Conformal Theory, AdS4 / CFT3 and localized gravity

Costas Bachas (ENS Paris)
Wednesday, March 27, 2013 - 10:30
Leuven 200D 05.34

I will discuss the supergravity duals of 1/2 BPS domain walls of N=4 super Yang-Mills theory in  4 dimensions, and of the closely-related  N=4 superconformal theories in 3 dimensions.  I will comment on the relevance of this work for the problem of localization of gravity, and also for the localized M2/M5 intersection  in 11 dimensions

 

A zig zag index

Antonia Amariti (ENS Paris)
Wednesday, March 27, 2013 - 10:30
Leuven 200D 05.34

I review some basic aspects of the superconformal index and give a simple derivation of the one loop determinants. After this I specialize on the large N index for N=1 4d SCFT describing D3 branes on toric CY singularity. This index is known to factorize over a set of BPS mesons. I show how to relate them to  the zig zag paths over the brane tiling and obtain some new result for families with orbifold singularities. I conclude with a geometric formulation of the index in terms of the toric diagram and the (p,q)-web.

 

AdS/Ricci-flat correspondence and the Gregory-Laflamme instability

Blaise Gouteraux (NORDITA)
Wednesday, March 20, 2013 - 10:30
Brussels, Solvay Room

We show that for every asymptotically AdS solution compactified on a torus there is a corresponding Ricci-flat solution obtained by replacing the torus by a sphere, performing a Weyl rescaling of the metric and appropriately analytically continuing the dimension of the torus/sphere (as in generalized dimensional reduction). In particular, it maps Minkowski spacetime to AdS on a torus, the holographic stress energy tensor of AdS to the stress energy tensor due to a brane localized in the interior of spacetime and AdS black branes to (asymptotically flat) Schwarzschild black branes. Applying it to the known solutions describing the hydrodynamic regime in AdS/CFT, we derive the hydrodynamic stress-tensor of asymptotically flat black branes to second order, which is constrained by the parent conformal symmetry. We compute the dispersion relation of the Gregory-Laflamme unstable modes through cubic order in the wavenumber, finding remarkable agreement with numerical data.

 

Aspects of Universality in Gauge/Gravity Duality

Johanna Erdmenger (Munich MPI)
Wednesday, March 20, 2013 - 13:00
Brussels, Solvay Room

 

High energy gravitational scattering and black-hole quantum hair

Gabriele Veneziano (CERN & Cikkege de France)
Friday, March 15, 2013 - 14:00
Brussels, Solvay Room

After a short review of previous results on the transplanckian scattering of light strings I will consider the case of the scattering of a light string on a "stringhole", a heavy string lying on the so-called correspondence curve between strings and black holes. I will argue that the corresponding S-matrix is perturbatively sensitive to properties of the microstate of the stringhole such as its quadrupole moment. Possible implications of such quantum hair on the black-hole information puzzle will be briefly discussed.

 

Extra dimensions, black holes and fireballs at the LHC

Anastasios Taliotis (VUB)
Wednesday, March 13, 2013 - 10:30
Brussels, Solvay Room

The collision of two gravitationally interacting, ultra-relativistic, extended sources is being examined. This investigation classifies the transverse distributions that are collided  according to whether one or two (a small and a large) apparent horizons may or may not be formed in a flat background in 4 dimensions. The study suggests a universal behavior in the produced entropy and, the elimination of the possibility in observing black holes (BHs) at the LHC in the absence of extra dimensions. On the other hand, including extra dimensions, and assuming that the matter is localized (dense) enough in those directions, opens new avenues in creating BHs at TeV scales.   The investigation is carried further to $AdS_5$ backgrounds and makes connections with QGP. In particular,  it seems that a BH is formed if and only if the (central collision) energy is sufficiently large compared to the transverse scale of the corresponding gauge theory side stress-tensor. This implies that a result, which is in accordance with the current intuition and data: QGP is formed only at high enough energies compared to $\Lambda_{QCD}$, even for central processes. Incorporating weak coupling physics and in particular the Color Glass Condensate (CGC) model, a satisfactory fitting with the RHIC and the LHC data for multiplicities may be established.

 

Quantum Computation vs. Firewalls

Daniel Harlow (Princeton)
Wednesday, March 13, 2013 - 13:00
Brussels, Solvay Room

Almheiri, Marolf, Polchinski, and Sully (AMPS) have recently argued that unitary of black hole evaporation is inconsistent with a smooth horizon as seen by an infalling observer. In this talk I briefly review their argument and then discuss recent work with Patrick Hayden, in which we argue that due to quantum computational restrictions the type of thought experiment used by AMPS to motivate their setup cannot be done in practice.

 

New perspectives on Black Holes in gauged Supergravity

Alessandra Gnecchi (Utrecht)
Wednesday, March 6, 2013 - 10:30
Brussels, Solvay Room

Interest on black holes solutions of N=2 gauged Supergravity has been revived recently, following the construction of supersymmetric regular black holes in asymptotic AdS_4 space.  We discuss these solutions, and in particular the scalar flow and attractors in N=2 minimally gauged Supergravity, in a duality covariant formulation. We focus on the regular 1/4-BPS solutions, comparing them to the previously known, singular, 1/2-BPS ones, and present an extension to extremal non supersymmetric black holes. We finally underline possible outcomes for holography and microstates counting.

 

Tracing is accelerating

Bartek Czech (Stanford)
Wednesday, March 6, 2013 - 13:00
Brussels, Solvay Room

Take a spatial slice of a spacetime and define a region D and its complement D-bar. In a holographic setup, for special choices of D, the area of $\partial D$ matches an entanglement entropy in the boundary theory. From a gravitational point of view, the entanglement is between quantum gravity microstates of (the domains of dependence of) D and D-bar. An operational way to measure the entanglement entropy S_D purely in gravity is to avoid looking at D-bar, i.e. to accelerate away from it. As an example, I will compute the entropy of a spacetime seen by a family of observers, who all accelerate radially from a common point – this is the entropy of Minkowski space with a spherical hole. This leads to some interesting consequences: (1) Areas of spherical surfaces in AdS predict the structure of UV-IR entanglement in strongly coupled field theories. (2) While the Schwarzschild black hole has an entropy, the Kruskal spacetime does not. (3, unsettled) Are there firewalls?

 

Recent progress on the de Sitter S-matrix

Ian Morrison (Cambridge)
Wednesday, February 27, 2013 - 10:30
Leuven 200E 01.207

The scattering matrix is an invaluable tool for studying quantum fields on global de Sitter space. In this talk I will review earlier work which establishes the S-matrix for perturbative QFTs (arXiv:1209.6039). I will then describe ongoing work on incorporating gravitons in perturbation theory. I will also describe aspects of the exact S-matrix of the principal chiral model.

 

5d gauge theories and their AdS(6) duals

Diego Rodriguez-Gomez (Oviedo)
Wednesday, February 27, 2013 - 13:00
Leuven 200E 01.207

Although 5d gauge theories are naively non-renormalizable, in certain cases they can be at fixed points. These fixed points exhibit quite amusing properties, such as enhanced E-type global symmetries. In this talk we will introduce three infinite families of 5d gauge theories of quiver type which can be put at a fixed point. The theories are engineered in a configuration of D4 branes probing an orbifolds of Type I' string theory, and we argue that they are dual to AdS_6xS^4 warped backgrounds; which in particular demonstrates the existence of such fixed points for quiver-type theories.

 

Gauged Supergravities in Different Frames

Mario Trigiante (Turin Polytech & INFN, Turin)
Wednesday, February 20, 2013 - 10:30
Brussels, Solvay Room

In this seminar I will emphasize the physical relevance of the choice  of the 'symplectic frame', namely  the initial definition of electric  and magnetic vector potentials, in the construction of gauged  supergravity models. After reviewing the embedding tensor  formulation  of gauged sueprgravities, I will illustrate how using the freedom in  the initial choice of the symplectic frame, new maximal supergravities  with  SO(8) local symmetry were recently constructed. This freedom is  built in the embedding tensor approach and is essential  in order to  capture the  low energy dynamics of different superstring/M-theory  compactifications.

 

Holography for Lifshitz spacetimes

Simon Ross (Durham)
Wednesday, February 20, 2013 - 13:00
Brussels, Solvay Room

I'll review the development of a holographic description of field theories with anisotropic scaling symmetries through asymptotically Lifshitz spacetimes. I will also discuss recent results on alternative boundary conditions for scalar fields in the bulk, which lead to a surprisingly high lower bound on the conformal dimensions of scalar operators in the field theories.

 

The heterotic string at high temperature (or with strong supersymmetry breaking)

Waldemar Schulgin (ULB)
Wednesday, February 13, 2013 - 10:30
Brussels, Solvay Room

Perturbative heterotic string theory develops a single complex tachyonic mode beyond the Hagedorn temperature. We calculate the quartic effective potential for this tachyonic mode at the critical temperature. Equivalently, we determine the quartic effective potential for strong supersymmetric breaking via anti-perdiodic boundary conditions for fermions on a small circle. We give many details of the heterotic tachyon scattering amplitudes, including a unitarity check to fix all normalization constants. We discuss difficulties in obtaining an effective action valid at all radii. We argue that in certain variables, the quartic term in the potential is radius independent. Speculations on the properties of a new strongly curved phase that could occur after tachyon condensation are offered.

 

Higher spin action and amplitudes

Per Sundell (UMons)
Wednesday, February 13, 2013 - 13:00
Brussels, Solvay Room

I will discuss recent progress in formulating higher spin gravities off-shell and computing conserved quantities and amplitudes within this context

 

Diffeomorphism Invariance and Non-relativistic Holography

Andreas Karch (U. Washington, Seattle)
Wednesday, December 12, 2012 - 13:00
Brussels, Solvay Room

Non-relativistic diffeomorphisms are symmetries of a large class of non-relativistic quantum field theories, including the quantum Hall states and the unitary Fermi gas. Based on these symmetries, we argue that generic many-body quantum mechanical systems have a dual holographic description in terms of a modified theory of gravity known as Horava gravity. Explicit examples of this duality embedded in string theory are constructed by starting with relativistic dual pairs and taking a non-relativistic scaling limit. Theories with relativistic parents however only realize a very small subset of the large landscape of non-relativistic field theories with Horava gravity duals.

 

Universal features of the Quark-gluon Plasma and 5D Holography

Umut Gursoy (Utrecht)
Wednesday, December 12, 2012 - 10:30
Brussels, Solvay Room

There is strong evidence that the quark-gluon plasma that is produced at RHIC and LHC can be described as a strongly interacting fluid. Assuming that it is at equilibrium at finite a temperature in the deconfined phase, I will present a phenomenological holographic description in terms of a black-hole in 5D coupled to a scalar field. I will focus on certain universal and qualitative features of the thermodynamic and hydrodynamic properties of the plasma, such as the profile of the interaction measure and the viscosity parameters in temperature that follows from the holographic model.

 

An infallin observer in AdS/CFT

Kyriakos Papadodimas (Amsterdam)
Wednesday, December 5, 2012 - 13:00
Brussels, Solvay Room

I will describe the experience of an observer falling into a black hole using the AdS/CFT correspondence. Our description of the black hole interior in terms of CFT operators provides a natural realization of black hole complementarity and a method of preserving unitarity without firewalls.   talk based on:  http://arxiv.org/abs/1211.6767

 

Brane instantons and fluxes in F-theory

Luca Martucci (INFN Padua)
Wednesday, December 5, 2012 - 10:30
Brussels, Solvay Room

Several phenomenological applications in string theory are based on the combination of two ingredients: background fluxes and non-perturbative effects.  With such applications in mind, I will discuss non-perturbative effects generated by Euclidean D3-branes (E3-branes) in F-theory flux compactifications. I will describe a new form of the  fermionic effective action of the E3-brane, in which the fermions are topologically twisted and the dynamical effect of bulk and world-volume fluxes, non-trivial axio-dilaton and warping is taken into account. I will discuss the structure of fermionic zero modes, which determine the form of  the associated non-perturbative superpotential and F-terms in the four-dimensional effective action.  Furthermore, I will discuss how to translate the results in terms of the dual M5-brane instanton in the M-theory picture. 

 

Partition functions of N=4 Yang-Mills and applications

Jan Manschot (Bonn)
Wednesday, November 28, 2012 - 13:00
Leuven

I will explain how to evaluate partition functions of N=4 U(r) Yang-Mills theory on a class of four-manifolds. Applications of these functions for electric-magnetic duality, geometric engineering of quantum field theories and D3-brane instanton corrections will also be discussed.

 

Supersymmetry on Curved Spaces and Holography

Claudius Klare (Milan)
Wednesday, November 28, 2012 - 10:30
Leuven

Supersymmetric field theories on curves spaces have recently attracted interest in the context of localization and exact results in QFT. I will discuss the existence of supersymmetric theories on Euclidean and Lorentzian manifolds, with a view towards holographic applications. In particular, I will present the constraints upon the space-time geometry coming from supersymmetry. In the superconformal case, I will show how the (possibly curved) space-time arises as the boundary geometry of a gravity dual.

 

On the applicability of linearized gravity in the description of homogeneous processes of holographic thermalization.

Michal Heller (Amsterdam)
Wednesday, November 21, 2012 - 13:00
Brussels

One of the most interesting recent trends on the arXiv are the studies of thermalization processes in strongly coupled field theories with the use of holographic techniques.  Such investigations are rather complicated, as typically they involve working with numerical solutions of the Einstein's equations in AdS obtained with the use of fully fledged numerical relativity codes. In this talk I will show that, at least in some cases, the gravitational description can be very much simplified to solving linearized Einstein's equations alone. I will focus mostly on the holographic isotropization from arXiv:1202.0981, but my talk will cover also some preliminary results from undergoing studies of the gravity dual to the boost-invariant flow.

 

Dark Radiation in the LARGE volume scenario

Joe Conlon (Oxford)
Wednesday, November 21, 2012 - 10:30
Brussels

The LARGE Volume Scenario is a promising approach to moduli stabilisation in string compactifications, in which the extra-dimensional volume is stabilised at an exponentially large value. I review the basic structure and properties of this scenario, and in particular the moduli spectrum.  The moduli spectrum always contains a massless axion as the partner to the volume modulus. I explain how the cosmological evolution of moduli and their decays implies this axion should be present as dark radiation - additional non-Standard Model radiation in the early universe, for which several experiments find preliminary hints.

 

Gauged N=4 supergravity from Calabi-Yau threefolds

Hagen Triendl (Saclay)
Wednesday, November 14, 2012 - 13:00
Brussels

For Calabi-Yau compactifications it is well-known that certain perturbative quantum corrections vanish if the Euler number is zero. We find a gauged N=4 supergravity action associated to such Calabi-Yau compacitifications that explains the vanishing of these corrections and might predict further simplifications. In particular, we argue that Calabi-Yau manifolds of Euler number zero are examples of (torsionful) SU(2)-structure manifolds and derive via dimensional reduction the gauged N=4 supergravity for general SU(2)-structure manifolds. Furthermore, we give examples of such SU(2)-structures on Calabi-Yaus, discuss spontaneous partial supersymmetry breaking and how these techniques might be used to better understand non-perturbative corrections on such spaces.

 

The back-reaction of anti-branes in warped fluxes compactification

Stanislav Kuperstein (IPhT Saclay)
Wednesday, November 14, 2012 - 10:30
Brussels

We study the full back-reaction of anti-D3 branes smeared over the tip of the deformed conifold. Requiring the geometry near the tip to be that of anti-D3 branes, we find simple arguments showing that if the three-form fluxes have no IR singularity, the only possible UV regular background is the anti-Klebanov-Strassler solution. Hence there is no regular solution whose D3-charge is negative in the IR and positive in the UV. We then analyze the solution with singular IR fluxes and demonstrate that the singularity cannot be resolved by the effects of brane polarization and therefore appears to be unphysical.

 

New SCFTs From Wrapped Branes

Brian Wecht (Queen Mary)
Wednesday, October 31, 2012 - 13:00
Leuven 200E 01.207

In string/M-theory, it is possible to engineer a wide variety of interesting supersymmetric conformal field theories (SCFTs) by wrapping branes on nontrivial manifolds. In this talk, I will describe a new infinite set of theories which come from M5-branes on Riemann surfaces. The corresponding supergravity solutions interpolate between, and extend beyond, a famous pair of solutions by Maldacena and Nuñez. Additionally, the dual SCFTs are "non-Lagrangian" theories, which have no weakly coupled UV descriptions, yet can (and will) be described explicitly.

 

Higher spin black hole entropy in 3D

Ricardo Troncoso (CECs Chile)
Wednesday, October 31, 2012 - 10:30
Leuven 200E 01.207

A new formula for the entropy of three-dimensional black holes endowed with spin-3 fields is proposed, which depends on the area and the value of the spin-3 field at the horizon. It is constructed by requiring the first law of thermodynamics to be fulfilled in terms of the global charges obtained through the canonical approach. In the weak spin-3 field limit, our result reduces to the one of Campoleoni, Fredenhagen, Pfenninger and Theisen, which has been recently found through a different approach.

 

Matter at a Finite Density: the Devious Fermion Signs

Jan Zaanen (Solvay Chair)
Wednesday, October 24, 2012 - 13:00
Brussels, Solvay Room

‘When dealing with strongly interacting fermion systems at a finite density, one encounters a non-probablistic structure that severs the connection with the powerful machinery of quantum field theory, resting in turn on statistical physics. This sign problem is conventionally viewed as a technicality spoiling the progress in the use of numerical methods. However, forced by empirical circumstances the awareness has been growing in the condensed matter community that the signs might be ‘the’ fundamental problem, obscuring our mathematical understanding of nature. The bright side is that this opens up plenty of room for surprises in the form of new states of matter governed by ‘signful’ emergence principles. The AdS/CFT correspondence appears to be the first working ‘sign processing’ mathematical machine. Are the recently discovered holographic strange metals ruled by such new sign principles? As a training for the mind I will present two condensed matter stories that shed some light on the depth of the fermion sign mystery: 1. Geometrizing the signs with Ceperley’s constrained path integral: the conformal state of Fermions and the fractal nodal surface. 2. Mottness versus Weng statistics: the dynamical signs behind RVB superconductivity.’

More information: http://www.solvayinstitutes.be

 

Hilbert Series and Supersymmetric Gauge Theories

Rak-Kyeong Seong (Imperial)
Wednesday, October 17, 2012 - 13:00
VUB D3.16

Studying moduli spaces is an integral part of understanding various properties of supersymmetric gauge theories. Hilbert series are generating functions of gauge invariant operators and play a prominent role in characterizing a moduli space. An introduction to Hilbert series is given, with examples from quiver gauge theories with toric Calabi-Yau moduli spaces as well as from a set of quiver theories of recent interest.

 

Strange Metals in One Spatial Dimension

Kareljan Schoutens (UVA)
Wednesday, October 10, 2012 - 13:00
Leuven 200E 01.207

We consider 1+1 dimensional SU(N) gauge theory coupled to a multiplet of massive Dirac fermions transforming in the adjoint representation of the gauge group.  The high density limit is characterized by a deconfined Fermi surface state with Fermi wavevector equal to that of free gauge-charged fermions. Its low energy fluctuations are described by a coset conformal field theory with central charge c=(N^2-1)/3. It displays an emergent N=(2,2) supersymmetry as well as extensive higher spin W-symmetries. We determine the exact scaling dimensions of the operators associated with Friedel oscillations and pairing correlations.

 

Non-Abelian T-duality in type--II Supergravity

Kostas Sfetsos (Surrey)
Wednesday, October 10, 2012 - 10:30
Leuven 200E 01.207

We review aspects of non-Abelian T-duality in type-II supergravity in the presence of non-trivial RR flux fields. We examine issues related to supersymmetry as well as the relevance of the new supergravity solutions which we construct within the AdS/CFT correspondence.

 

Massive higher-derivative gravity: beyond spin-2 and beyond 3D

Yihao Yin (University of Groningen)
Wednesday, October 3, 2012 - 13:00
VUB D3.16

General Relativity in 3D does not describe any propagating gravitons. However, massive gravitons can be introduced into the theory by adding extra higher-derivative terms. Two well-known examples are "New Massive Gravity" (NMG) and "Topological Massive Gravity" (TMG). In my presentation, I will interpret the linearized NMG and TMG models from the perspective of the Fierz-Pauli equations, and show that they belong to a general procedure that allows one to construct, in the free case, higher-derivative gauge theories for different spins in various dimensions.

 

Anti-brane singularities as an indication of instabilities

Thomas Van Riet (Saclay, KU Leuven)
Wednesday, October 3, 2012 - 10:30
VUB D3.16

In this talk I discuss the singularities of anti-D6 branes in a flux background that carries opposite charge to anti-branes. After three T-dualities this relates to singular anti-D3 solutions. The focus of the whole talk will not be on the technicalities but on the simple physical picture that emerges when one interprets these singularities as due to perturbative instabilities. If correct, this implies that anti-branes cannot be used to uplift AdS vacua.