
Past seminars
Academic year: September 2009  September 2010
The setting of general relativity in Dspacetime dimensions revealed different species of black holes with exciting new properties. Remarkably, in D>4, the behavior of certain fast (ultra) spinning black holes and black rings changes qualitatively to that of extended black branes and strings. Identifying which black holes exhibit a black string/membrane phase is essential not only to have a better understanding of their thermodynamical and classical instability but also to discern which of them could be captured by long distance effective approaches. We will overview a catalogue of currently known black hole species and focus on the thermodynamical properties, phases and instabilities of black holes with at least two angular momenta.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, June 9, 2010 at 13:00
Today great efforts are devoted to the study of ultracold atomic gases trapped in optical traps. The remarkable versatility offered by these elegant setups allows experimentalists to engineer powerful quantum simulators. In other words, these pure and controllable atomic systems can be designed in order to reproduce the dynamics of more complex quantum systems. Such quantum simulators are therefore well suited to explore the effects stemming from condensedmatter and even high energy physics. In this context, the realization of synthetic magnetic fields for neutral atoms, based on the Berry's phase, could lead to the exploration of the fractional quantum Hall states and their anyonic features. Furthermore, generalizations of similar setups lead to the realization of static nonAbelian gauge fields. In this talk, I will give an introduction to these artificial gauge fields and describe how they lead to the investigation of topological insulators and lattice gauge theories.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, June 9, 2010 at 10:30
In this talk I will review G2 dualities of minimal five dimensional supergravity. I will report new extremal (both supersymmetric and nonsupersymmetric) black strings recently constructed using these dualities. I will discuss a general nonextremal black string in this theory that captures the above mentioned extremal strings and provides a setting for examining microscopics of thermally excited black rings.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, June 2, 2010 at 13:00
According to the celebrated Gauge/String dualities, problems of (multicolor) quantum Gauge Theory may be rephrased in terms of (classical) String Geometry. On the side of string theory, part of the information is encoded in the spectrum of novel 1dimensional quantum systems with a number of unconventional features. In my talk I will outline some of the analytical and numerical tools that were developed recently to study such systems and I will review some of the main new results.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, June 2, 2010 at 10:30
We review some of the basic properties of superfluids. We focus on two apparently different systems: cold fermionic atoms close to the unitarity limit and cold dense quark matter in the color superconducting phase. The low energy properties of both systems and their transport properties will be analyzed employing the effective field theory of the phonon field. Since quarks have color, flavor as well as spin degrees of freedom many different color superconducting phases can be realized. We shall restrict to the socalled color flavor locked phase. Results for superfluids with mismatched Fermi spheres will also be presented.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, May 26, 2010 at 13:00
In this talk, I will present new nonBPS solutions of 5D supergravity coupled to three U(1) gauge fields. Some of these solutions correspond to black holes, but some are smooth, horizonless geometries. I will present how these solutions have been found starting very close from the BPS ones, and then trying to going farther from "BPSness", and discuss their properties.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, May 26, 2010 at 10:30
Recent progress in our understanding of the AdS/CFT correspondence for M2branes has renewed our desire to classify elevendimensional supergravity backgrounds which are dual to threedimensional superconformal field theories. The geometries dual to N<4 superconformal theories are reasonably generic and probably hard to classify, but those dual to N>3 superconformal theories admit a very nice classification in terms of ADE Dynkin diagrams (via the McKay correspondence). I will present this classification in this talk.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, May 12, 2010 at 13:00
Since the theoretical discovery of black hole evaporation through Hawking radiation the question of the unitarity of its evolution has been a major challenge for our understanding of black hole physics and of quantum physics in general.
One seems to be faced with a problematic alternative: either there is, as in the original Hawking derivation, no information in the thermal state and unitarity is violated, or the original information is contained in the radiation and hence unitarity is preserved. The present work is an attempt to transcend the alternative by showing how the Hawking derivation can emerge from a unitary black hole Smatrix in a semiclassical approximation.
In our approach, the Smatrix unitarity follows from an analysis of exclusive Smatrix amplitudes while the semiclassical approximation emerges from the inclusive ones. The scheme, which is is inspired by the work of 't Hooft and Susskind and by some of our previous considerations, makes contact with recent conjectures. It rests on ordinary quantum theory in the sense that although the computation of the unitary amplitudes would require a welldefined theory of quantum gravity, the scheme itself does not.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, May 12, 2010 at 10:30
Slides of the talk
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, May 5, 2010 at 13:00
We discuss multimetric extensions of Einstein gravity containing N copies of standard model matter and a corresponding number of metrics. For N=2 we can prove a nogo theorem that forbids gravity theories that admit a Newtonian limit with attractive gravitational forces within each matter sector, and repulsive forces of the same strength between matter from different sectors. This type of theory becomes possible for N>2 where we can provide a simple explicit model. We apply this theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way dark energy could be explained simply by dark copies of the wellunderstood standard model.
Slides of the talk
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, May 5, 2010 at 10:30
Recent results suggest the quarkgluon plasma created in heavy ion collisions at RHIC is in a strongly coupled regime and the AdS/CFT correspondence has proved more successful at describing the equilibrium behaviour of the plasma than previous weakcoupling theoretical predictions. The equilibration of the thermal plasma is dual to a black hole formation process in the AdS bulk. We model this process with a collapsing scalar shell. Outside the shell the metric is well approximated by that of a black brane, and onepoint functions which are only sensitive to the physics near the boundary appear instantaneously thermalised. However, twopoint functions and Wilson loops in the field theory (calculated by finding geodesics and minimal surfaces which end on the boundary and extend into the bulk in AdS) will vary as the shell collapses. We use these to probe the thermalsiation in the dual field theory. This work is ongoing and I will present current progress.
Place: Leuven, Celestijnenlaan 200D 05.11
Time: Wednesday, April 28, 2010 at 13:00
In this talk I discuss a recently discovered analytic solution of open string field theory describing the endpoint of tachyon condensation. The solution can be cast in an appealing algebraic framework, and the proof of Sen's conjectures follows from only a few lines of calculation. The solution represents a culmination of impressive advances in our understanding of string field theory, back from the days when the stable vacuum of the open string tachyon could only be understood numerically, by approximating an infinite number of coupled nonlinear field equations.
Place: Leuven, Celestijnenlaan 200D 05.11
Time: Wednesday, April 28, 2010 at 10:30
AdS2/CFT1 correspondence leads to a prescription for computing the degeneracy of black hole states in terms of path integral over string fields living on the near horizon geometry of the black hole. In this talk, I will discuss about how to make use of the enhanced supersymmetries of the near horizon geometry and localization techniques to argue that the path integral receives contribution only from a special class of string field configurations which are invariant under a subgroup of the supersymmetry transformations. I will identify saddle points which are invariant under this subgroup. I will also use this analysis to show that the integration over infinite number of zero modes generated by the asymptotic symmetries of AdS2 generate a finite contribution to the path integral.
Slides of the talk
Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Salle des Professeurs
Time: Wednesday, April 21, 2010 at 13:00
CANCELLED
The setting of general relativity in Dspacetime dimensions revealed different species of black holes with exciting new properties. Remarkably, in D>4, the behavior of certain fast (ultra) spinning black holes and black rings changes qualitatively to that of extended black branes and strings. Identifying which black holes exhibit a black string/membrane phase is essential not only to have a better understanding of their thermodynamical and classical instability but also to discern which of them could be captured by long distance effective approaches. We will overview a catalogue of currently known black hole species and focus on the thermodynamical properties, phases and instabilities of black holes with at least two angular momenta.
Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Salle des Professeurs
Time: Wednesday, April 21, 2010 at 10:30
Visit the website of the IAP Day
Place: ULB, Campus Plaine, Forum A
Time: Thursday, April 8, 2010
I will review the recent results relating quiver matrix models to 2d conformal Toda field theories and 4d N=2 quiver gauge theories. I will also discuss some connections to topological strings.
Place: Leuven, Celestijnenlaan 200E 01.209
Time: Wednesday, March 31, 2010 at 13:00
In the first part of the talk I will review the construction of ChernSimons quivers with N=2 supersymmetry in 3 dimensions, which are expected to flow to an interacting SCFT in the IR. I will review the Mtheory/string theory construction of these quivers, which is very much related to the same problem for D3branes at singularities in type IIB. Particular emphasis will be given on the emergence of the M theory direction at strong coupling, and its relation to monopole operators in the ChernSimons quiver. In the second part of the talk, I will explain that for M2branes at toric CalabiYau fourfolds with nonisolated singularities, a natural description of the dual quiver is in term of quivers with flavors. This is possible only if there is a particular nontrivial OPE between monopole operators, which we conjecture.
Place: Leuven, Celestijnenlaan 200E 01.209
Time: Wednesday, March 31, 2010 at 10:30
We study Vasiliev's higher spin gauge theory in AdS4 and partially confirm a conjecture of SezginSundellKlebanovPolyakov by computing the tree level three point functions.
Place: Mons, Batiment Pentagone, Salle 0A11
Time: Wednesday, March 24, 2010 at 13:00
I will present a personal view of the current status of the theory of HigherSpin Gauge fields, with emphasis on some of the progress attained during the last few years and on some of the key challenges for the near future.
Place: Mons, Batiment Pentagone, Salle 0A11
Time: Wednesday, March 24, 2010 at 10:30
After a review of universal analytic solutions in OSFT and of the proof of first and second Sen's conjectures, we present new exact results which can be relevant to construct lower dimensional branes solutions and to prove Sen's third conjecture.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, March 17, 2010 at 13:00
We construct a simple set of conditions for having a classical dS solution of type IIA supergravity and present an example on the group manifold SU(2)xSU(2).
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, March 17, 2010 at 10:30
After summarizing basic properties of higherspin gauge theory with some emphasize on the unfolded dynamics approach and its relation with the BRST approach, recent results on free conformal higherspin models of general type will be presented. In particular, it will be shown how dynamical fields, gauge symmetries and gauge invariant tensors in the theory are associated to supersymmetric vacua of certain supersymmetric matrix models.
Place: Leuven, Celestijnenlaan 200E 01.209
Time: Wednesday, March 10, 2010 at 13:00
In recent years increasing theoretical attention has been directed towards the maximally supersymmetic theories, because of their unique properties and richness of beautiful structures. In four dimensions N=4 superYangMills and N=8 supergravity are paramount examples of such theories, owing much of their fame due to their hidden stringy nature, revealed in the AdS/CFT duality and Mtheory lowenergy limit, respectively. Similarly, in recent years there has been a veritable revolution in the field of perturbative calculations, leading to new efficient methods for computing scattering amplitudes using the old ideas of unitarity and analyticity of the Smatrix. Besides their phenomenological applications, the new methods are excellent tools in the perturbative studies of the maximally supersymmetric theories, shedding new light on the AdS/CFT duality and on the possibility of N=8 supergravity being the first example of an ultraviolet finite gravity theory with pointlike particles.
In this talk I will discuss the process of computing multiloop scattering amplitudes in N=4 superYangMills and N=8 supergravity. The calculations are based on the unitarity method, which together with the simple structure of the maximally supersymmetric theories allows one to probe these theories to high loop orders. In particular, I will discuss the structure of the fourpoint amplitudes, which are calculated up to four loops. By analyzing the potential ultraviolet divergences of the amplitudes we obtain that N=8 supergravity is finite through four loops. Even more remarkably, we show that N=8 supergravity obeys the same power counting bound as the allorder finite N=4 superYangMills theory, providing direct evidence of the claimed ultraviolet finiteness of N=8 supergravity.
Place: Leuven, Celestijnenlaan 200E 01.209
Time: Wednesday, March 10, 2010 at 10:30
These lectures are aimed to provide an introduction to Ftheory compactifications with the motivation to build fourdimensional GUT models. The main focus will be on the basics of the formulation of Ftheory itself, its connection with Mtheory, and the weak coupling orientifold picture. Starting from a GUTlike model in the orientifold picture, the construction of consistent Ftheory GUTs will be discussed briefly in the last part of the talks.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, March 3, 2010 at 13:00
These lectures are aimed to provide an introduction to Ftheory compactifications with the motivation to build fourdimensional GUT models. The main focus will be on the basics of the formulation of Ftheory itself, its connection with Mtheory, and the weak coupling orientifold picture. Starting from a GUTlike model in the orientifold picture, the construction of consistent Ftheory GUTs will be discussed briefly in the last part of the talks.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, March 3, 2010 at 10:30
I will introduce the basic aspects of supersymmetry breaking and its realization in the MSSM. I will review the gauge mediation mechanism and its general formulation. I will then describe Semi Direct Gauge Mediation (SDGM) and I will introduce a model independent description for it. From this description I will extract the main phenomenological signatures, namely the pattern of soft masses. I will finally discuss how to combine SDGM with other known mediation mechanism in order to obtain a sensible superpartner spectrum.
Place: Leuven, Celestijnenlaan 200D 05.11
Time: Wednesday, February 24, 2010 at 13:00
Onedimensional defect lines have become an important tool in studying twodimensional conformal field theories and their perturbations. I shall review the notion of topological defect lines and explain how they can be used to obtain information on renormalisation group flows. The minimal models will serve as my main example to illustrate the ideas. In particular, I shall discuss recent results on coupled bulk and boundary flows in these models.
Place: Leuven, Celestijnenlaan 200D 05.11
Time: Wednesday, February 24, 2010 at 10:30
The dynamical consistency of the nonprojectable version of Hořava gravity is investigated by focusing on the asymptotically flat case. It is argued that for generic solutions of the constraint equations the lapse must vanish asymptotically, or even everywhere in particular cases. Put differently, the Hamiltonian constraints are generically all secondclass, revealing a dynamical inconsistency of the theory. A seeming paradox will be resolved and implications of the result will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, February 17, 2010 at 13:00
In recent years Higgsless models have been considered following different approaches. The underlying idea is the possibility of a new strong interaction at the scale of few TeV, as in Technicolor case. However due to the theoretical difficulty in dealing with strong interacting theories, effective models have been considered. I will show you that moose models offer a good basis for this approach (also for their interpretation in five dimensions) and also that several old models can be reviewed within this framework. I will discuss the main problems affecting all these approaches, namely unitarity and agreement with electroweak experimental data. I will show that these two problems create a tension that it is possible to solve only at the expense of some fine tuning. Possible phenomenological implications for the physics at the LHC will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, February 17, 2010 at 10:30
A central problem in quantum condensed matter physics is the critical theory governing the zero temperature quantum phase transition between strongly renormalized Fermiliquids as found in heavy fermion systems and possibly high Tc superconductors. We show that string theory is able to describe such fermionic quantum critical states. Using the AntideSitter/Conformal Field Theory (AdS/CFT) correspondence to relate fermionic quantum critical fields to a gravitational problem, we compute the spectral functions of fermions in the field theory. By increasing the fermion density away from the relativistic quantum critical point, a state emerges with all the features of the Fermiliquid.
References to the original work underlying the talk: Cubrovic, Zaanen and Schalm; Liu, McGreevy and Vegh and Faulkner, Liu, McGreevy and Vegh. Earlier related work by Lee and Rey.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, February 10, 2010 at 13:00
E11 is known to predict the correct physical fields of all maximal supergravities in D > 2, plus any possible gauge deformation thereof. In this talk I will explain whether or not this correspondence also holds in D=2, where the global symmetry group is E9.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, February 10, 2010 at 10:30
I will review Gaiotto's construction of N=2 SCFTs via M5branes wrapped on Riemann surfaces, including an alternative type IIB construction suitable to study their flavor symmetries, and net of new Sdualities relating them. Then I will focus on N=1 constructions, and the computation of central charges from supergravity. The method also gives some information on the recently discovered 2d4d correspondence with Toda theories.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 16, 2009 at 13:00
Deviations from the BunchDavies vacuum during an inflationary period can leave a testable imprint on the higherorder correlations of the CMB and large scale structures in the Universe. After an introduction of nonGaussian effects in inflation and a brief review of the motivations for a modified vacuum state, I will present recent results for the leading vacuum state corrected nonGaussian bispectrum in two cases of specific interest:
1) singlefield inflation with a canonical kinetic term plus a specific higher derivative correction and
2) general singlefield inflation in the limit of small sound speed. After projecting these results on the available observational templates, the enhanced levels of nonGaussianity are shown to result in relatively strong constraints on deviations from the BunchDavies state, with lots of room for improvement in the future.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 16, 2009 at 10:30
Recently, a class of solutions to the Type IIB system of Nc D5branes wrapped on S2 were found that exhibit walking behaviour, i.e. a suitably defined gauge coupling stays approximately constant over a large intermediate energy regime. These models provide interesting laboratories in which dynamical questions about the strongly coupled properties of walking theories can be addressed. One such question is whether the spontaneous breaking of scale invariance leads to the existence of a light scalar in the spectrum, the dilaton. In this talk, I will review results from an analytical and numerical study, which indicates the presence of such a light state, the mass of which is suppressed by the length of the walking region.
Place: Leuven, Celestijnenlaan 200D, room 06.32
Time: Wednesday, December 9, 2009 at 13:00
Place: Leuven, Celestijnenlaan 200D, room 05.34
Time: Wednesday, December 9, 2009 at 10:30
Gaugegravity duality is an extremely useful tool for studying stronglycoupled gauge theories, and has many applications to realworld systems, such as the quarkgluon plasma and quantum critical points. It is especially useful for studying the hydrodynamics of stronglycoupled nonAbelian gauge theories. For example, gaugegravity duality is currently the only reliable way to compute transport coefficients for many theories. In this talk I will describe a calculation of a transport coefficient, a conductivity, associated with flavor fields in a stronglycoupled plasma. From the result for the conductivity, I will show how gaugegravity duality captures a lot of realworld physics, such as momentum dissipation, Schwinger pair production, and more.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 2, 2009 at 13:00
In this talk we will study the nature of the nonperturbative corrections in gauge/strings dualities. We consider a toy model of gauge/string duality relating the ChernSimons theory on lens spaces to the topological string on toric CalabiYau's. We find a rich structure of large N phase transitions in the complex plane of the 't Hooft parameter. These transitions are due to the existence of nontrivial instanton sectors of the gauge theory, which compete among themselves. We argue that these large N phase transitions can be regarded as a deformation of the Stokes phenomenon. We show that, for generic values of the 't Hooft coupling, instanton effects are not exponentially suppressed at large N and they correct the genus expansion already at the next to leading order.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 2, 2009 at 10:30
In (supersymmetric) gauge theories realized on Dbrane worlds, classes of nonperturbative corrections can be derived by taking into account the presence of Dbrane instantons. Some of these latter correspond to the ordinary gauge theory instantons, other ones yield novel "stringy" or "exotic" nonperturbative effects, potentially of phenomenological relevance. To put on firm grounds the computation of the exotic contributions to the effective action, and to investigate their fieldtheoretic interpretation we focus first on an 8dimensional example, the D(1)/ D7 system in type I' theory. The gauge theory on the D7brane receives exotic corrections at all instanton numbers whose computation can be checked using the typeI/heterotic duality. We consider then a 4d example, a system of D(1)/D3/D7 branes in type I' on T4/Z2, which has similar features; however, this is only work in progress...
Place: Leuven, Celestijnenlaan 200D, room 06.32
Time: Wednesday, November 25, 2009 at 13:00
We obtain a holographic superconductor model in which 1) the field theory dual is explicitly known; 2) there is a stringtheoretical picture of the pairing mechanism. To achieve this, we consider thermal stronglycoupled N=2 Super YangMills theory with fundamental matter at finite isospin chemical potential. Using gauge/gravity duality, ie. a probe of two flavour D7branes embedded in the AdS black hole background, we find a critical temperature at which the system undergoes a second order phase transition. In the thermodynamically favoured phase, a flavour current acquires a vev and breaks an Abelian symmetry spontaneously. This new phase shows signatures known from superconductivity, such as infinite dc conductivity and a gap in the frequencydependent conductivity, as well as a remnant of the Meissner effect. The setup allows for an explicit identification of the degrees of freedom in the dual field theory, as well as for a dual string picture of the condensation process.
Place: Leuven, Celestijnenlaan 200D, room 05.34
Time: Wednesday, November 25, 2009 at 10:30
Motivated by the AdS4/CFT3 correspondence, I consider twolevel supersymmetric ChernSimons matter theories perturbed by the most general marginal superpotential compatible with N=2 supersymemtry. This class of models contain as particular cases perturbations of the ABJM/ABJ theories with and without flavors and N=2,3 theories with different CS levels. Within a perturbative approach, I discuss the complete spectrum of fixed points and their IR stability.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, November 18, 2009 at 13:00
It has been conjectured that higherdimensional rotating black holes become unstable at a sufficiently large value of the rotation, and that new black holes with pinched horizons appear at the threshold of the instability. In this talk, I will describe our numerical work where this threshold mode is found for the singly spinning MyersPerry black hole. This mode appears *after* the value of the rotation parameter for which the second derivative of the entropy with respect to the angular momentum vanishes. In the second part of the talk, I will describe our recent results for MyersPerry black holes with all the angular momenta equal. For this class of black holes, we have studied the explicit timedependence of the unstable modes. I will also comment on possible evidence for new stationary black holes with a single U(1) isometry.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, November 18, 2009 at 10:30
I will discuss asymmetric Z2 x Z2 heterotic orbifolds in the free fermionic language and the effects of the asymmetric projections on the spectrum of semirealistic models. I will present methods to investigate systematically the flat directions in such models and examine their potential to be examples with very few moduli.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, November 4, 2009 at 13:00
I will review the problem of spontaneous partial supersymmetry breaking in N=2 gauged supergravity. I will then discuss some current work which uses the embedding tensor approach to determine the general conditions under which N=2 to N=1 supersymmetry breaking is possible, and also provides a new perspective on stringy realisations.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, November 4, 2009 at 10:30
Almost all possible deformations of a supergravity theory come about by making local some global invariance of the theory. This can be for example the gauging of some isometry of the scalar manifold or some massive deformation that originates from making local some shift symmetry of a $p$form with p\ge 1. The local gauge symmetries of the deformed supergravity theory are encoded in a structure known as the tensor hierarchy. Since deforming supergravities leads to the introduction of potentials such considerations are relevant for o.a. low energy descriptions of flux compactifications of string theory. In this talk I will introduce the notion of a tensor hierarchy and use it to discuss the deformations of 4dimensional supergravities. After discussing the 4dimensional case to some detail I will outline what happens in higherdimensional cases. At the end I will comment on ``deformations'' of the type IIA/B supergravities.
Place: Leuven, Celestijnenlaan 200D, room 06.32
Time: Wednesday, October 28, 2009 at 13:00
It has been shown by Hertog and Horowitz that certain AdS boundary conditions allow nonsingular initial conditions to evolve into a Big Crunch. To study this kind of cosmological singularities, one can use the dual quantum field theory, where the singularity is manifested by the presence of a multitrace potential unbounded below. Recently, Craps, Hertog and Turok have proposed two specific models of this type to study the possibility of a Big Crunch/Big Bang transition. For these models, I will provide a Dbrane interpretation of the unbounded potential. In particular, I will show that the AdS boundary conditions of interest cause spherical Dbranes to be pushed to the boundary of AdS, and that the corresponding potential agrees with the multitrace deformation of the boundary field theory.
Place: Leuven, Celestijnenlaan 200D, room 05.34
Time: Wednesday, October 28, 2009 at 10:30
I will introduce topology of gauge fields responsible for baryon number violation in the Standard Model and describe physical mechanism behind this nonperturbative phenomenon. Then I proceed to the discussion of whether or not electroweak baryon number violation may occur at future high energy colliders. This will bring about a novel mechanism of tunnelingtype transitions in quantum systems with multiple degrees of freedom.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 21, 2009 at 13:00
I will report on ongoing work with Cesar Gomez and Raul Jimenez where we try to understand the interplay between supersymmetry, supergravity and inflationary cosmology.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 21, 2009 at 10:30
I will review the threedimensional superconformal N=6 theories of ABJM type, and explain that the threealgebras used by Bagger and Lambert can be described as generalized Jordan triple systems. Using this description, I will show that simple threealgebras are in onetoone correspondence with a certain type of simple Lie superalgebras.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 14, 2009 at 13:00
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 14, 2009 at 10:30
The lectures will explain the inflationary cosmological model and its virtues. In particular, what inflation predicts for density perturbations and gravity waves, and what could be alternatives, will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Thursday, October 8, 2009, 16:0018:00
The lectures will explain the inflationary cosmological model and its virtues. In particular, what inflation predicts for density perturbations and gravity waves, and what could be alternatives, will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 7, 2009, 16:0018:00
Understanding a quantum theory for gravity may pass through the understanding of the symmetries and dualities present in general relativity. One of those is gravitational duality, a sort of electromagnetic duality which was checked to be present in linearized general relativity. In the first part of this talk, I will review what I mean by gravitational duality and what is already known about it. I will then show how it works on specific examples and discuss a possible different interpretation for the source of the Kerr solution. In the second part, I will move to pure N=2 supergravity where the charged TaubNUT metric is a solution of the theory as we checked by finding explicitely its killing spinors. I will give arguments on how the supersymmetry algebra must be modified to take into account the NUT charge. This will finally lead us to the understanding of duality rotations on fermionic supercharges. I will eventually show how this idea should also be implemented in N=1 supergravity.
Place: Leuven, Celestijnenlaan 200E, room 01.209
Time: Wednesday, October 7, 2009 at 13:00
The renormalization group of scalar field theories of the Lifshitz type are studied, focusing in particular on the RG evolution of the ``speed of light'' coupling c2φ and, for more than one field, of δ c2 ∼ c2φ1c2φ2 in simple models. We find that in the UV both c2φ and δ c2 flow logarithmically with the energy scale. A logarithmic running of c2 persists also at low energies, if δ c2 ≠ 0 in the UV. As a result, Lorentz symmetry is not recovered at low energies with the accuracy needed to withstand basic experimental constraints, unless all the Lorentz breaking terms, including δ c2, are unnaturally finetuned to extremely small values in the UV.
Place: Leuven, Celestijnenlaan 200E, room 01.207
Time: Wednesday, October 7, 2009 at 10:30
The lectures will explain the inflationary cosmological model and its virtues. In particular, what inflation predicts for density perturbations and gravity waves, and what could be alternatives, will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Tuesday, October 6, 2009, 16:0018:00
The lectures will explain the inflationary cosmological model and its virtues. In particular, what inflation predicts for density perturbations and gravity waves, and what could be alternatives, will be discussed.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Monday, October 5, 2009, 16:0018:00
Knowledge gained so far in cosmology is to a large extent orthogonal to current knowledge in particle physics. There is matter and no antimatter in our Universe, and we do not have a unique explanation of this asymmetry. There is dark matter in the cosmos, and we do not know what the particles are it consists of. Cosmological expansion accelerates, and we do not know the fundamental physics behind this bizarre behavior. The origin of galaxies must have roots deep in quantum field theory, but we still have only a crude idea of what they are. Amazingly, all these mysteries will most probably be solved in a reasonably near future. I review these and other issues at the interface of particle physics and cosmology, with an emphasis on future progress in our understanding of the Universe.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Tuesday, September 29, 2009 at 16:00
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