Joint seminars academic year: 2009-2010
"Thermodynamic instability of doubly spinning black objects"
Maria J. Rodriguez (MPI Potsdam)
VUB/ULB – June 9, 2010
The setting of general relativity in D-spacetime 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
"Cold atoms subjected to synthetic gauge fields"
Nathan Goldman (ULB)
VUB/ULB – June 9, 2010
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 condensed-matter 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 non-Abelian 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
"G2 Dualities and Black Ring Microscopics"
Amitabh Virmani (ULB)
Leuven – June 2, 2010
In this talk I will review G2 dualities of minimal five dimensional supergravity. I will report new extremal (both supersymmetric and non-supersymmetric) black strings recently constructed using these dualities. I will discuss a general non-extremal 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
"String Geometry for Gauge Theory"
Volker Schomerus (DESY, Hamburg)
Leuven – June 2, 2010
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 1-dimensional 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
"Superfluidity in cold atoms and quark matter"
Massimo Mannarelli (UB)
Leuven – May 26, 2010
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 so-called 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
"From BPS to non-BPS black holes"
Clement Ruef (CEA Saclay)
Leuven – May 26, 2010
In this talk, I will present new non-BPS 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
" Supersymmetric M2-branes and A-D-E"
Jose Figueroa O'Farrill
Leuven – May 12, 2010
Recent progress in our understanding of the AdS/CFT correspondence for M2-branes has renewed our desire to classify eleven-dimensional supergravity backgrounds which are dual to three-dimensional 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 A-D-E 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
"The hidden horizon and black hole unitarity"
François Englert (ULB)
Leuven – May 12, 2010
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 S-matrix in a semi-classical approximation.
In our approach, the S-matrix unitarity follows from an analysis of exclusive S-matrix amplitudes while the semi-classical 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 well-defined theory of quantum gravity, the scheme itself does not.
Place: Leuven, Celestijnenlaan 200D 06.34
Time: Wednesday, May 12, 2010 at 10:30
"Superstring cosmology"
John Estes (Ecole Polytechnique)
VUB/ULB – May 5, 2010
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, May 5, 2010 at 13:00
"Repulsive gravity extensions and dark energy"
Mattias Wohlfarth (Hamburg, DESY)
VUB/ULB – May 5, 2010
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 no-go 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 well-understood standard model.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, May 5, 2010 at 10:30
"Probing Thermalisation of Quark-Gluon Plasma using AdS/CFT"
Neil Copland (VUB)
Leuven – April 28, 2010
Recent results suggest the quark-gluon 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 weak-coupling 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 one-point functions which are only sensitive to the physics near the boundary appear instantaneously thermalised. However, two-point 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
"A simple analytic solution for tachyon condensation"
Theodore Erler (Prague University)
Leuven – April 28, 2010
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
"Supersymmetry, Localization and Quantum Entropy Function"
Ipsita Mandal (Harish-Chandra Research Institute, Allahabad)
VUB/ULB – April 21, 2010
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.
Place: VUB/ULB, Campus Plaine, building NO, 9th floor, Salle des Professeurs
Time: Wednesday, April 21, 2010 at 13:00
"Thermodynamic instability of doubly spinning black objects"
Maria J. Rodriguez (MPI Potsdam)
VUB/ULB – April 21, 2010
CANCELLED
The setting of general relativity in D-spacetime 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
"IAP day at ULB, April 8 2010"
Visit the website of the IAP Day
Place: ULB, Campus Plaine, Forum A
Time: Thursday, April 8, 2010
"Matrix models, 2d CFTs and 4d N=2 gauge theories"
Niclas Wyllard (Chalmers)
Leuven – March 31, 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
"Chern-Simons theories with fundamental matter for M2-branes at generic toric singularities"
Cyril Closset (ULB)
Leuven – March 31, 2010
In the first part of the talk I will review the construction of Chern-Simons quivers with N=2 supersymmetry in 3 dimensions, which are expected to flow to an interacting SCFT in the IR. I will review the M-theory/string theory construction of these quivers, which is very much related to the same problem for D3-branes 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 Chern-Simons quiver. In the second part of the talk, I will explain that for M2-branes at toric Calabi-Yau fourfolds with non-isolated singularities, a natural description of the dual quiver is in term of quivers with flavors. This is possible only if there is a particular non-trivial OPE between monopole operators, which we conjecture.
Place: Leuven, Celestijnenlaan 200E 01.209
Time: Wednesday, March 31, 2010 at 10:30
"On higher spin gauge theory and holographic correspondence"
Xi Yin (Harvard University)
Mons – March 24, 2010
We study Vasiliev's higher spin gauge theory in AdS4 and partially confirm a conjecture of Sezgin-Sundell-Klebanov-Polyakov by computing the tree level three point functions.
Place: Mons, Batiment Pentagone, Salle 0A11
Time: Wednesday, March 24, 2010 at 13:00
"Recent progress in higher-spin gauge theory"
A. Sagnotti (Scuola Normale Superiore di Pisa)
Mons – March 24, 2010
I will present a personal view of the current status of the theory of Higher-Spin 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
"On lower dimensional D-branes in Open String Field Theory"
Carlo Maccaferri (ULB)
VUB/ULB – March 17, 2010
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
"Classical dS compactifications of type IIA compactifications"
Paul Koerber (KUL)
VUB/ULB – March 17, 2009
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
"Higher-Spin Gauge Theory: General Properties and Recent Results"
Misha Vasiliev (Lebedev Institute, Moscow)
Leuven – March 10, 2010
After summarizing basic properties of higher-spin gauge theory with some emphasize on the unfolded dynamics approach and its relation with the BRST approach, recent results on free conformal higher-spin 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
"Exploring Multiloop Amplitudes in Maximally Supersymmetric Theories"
Henrik Johansson (IPhT Saclay)
Leuven – March 10, 2010
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 super-Yang-Mills 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 M-theory low-energy 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 S-matrix. 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 point-like particles.
In this talk I will discuss the process of computing multiloop scattering amplitudes in N=4 super-Yang-Mills 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 four-point 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 all-order finite N=4 super-Yang-Mills 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
"F-theory compactifications for GUT model building - Part 2"
Thomas Grimm (University of Bonn)
VUB/ULB – March 3, 2010
These lectures are aimed to provide an introduction to F-theory compactifications with the motivation to build four-dimensional GUT models. The main focus will be on the basics of the formulation of F-theory itself, its connection with M-theory, and the weak coupling orientifold picture. Starting from a GUT-like model in the orientifold picture, the construction of consistent F-theory 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
"F-theory compactifications for GUT model building - Part 1"
Thomas Grimm (University of Bonn)
VUB/ULB – March 3, 2010
These lectures are aimed to provide an introduction to F-theory compactifications with the motivation to build four-dimensional GUT models. The main focus will be on the basics of the formulation of F-theory itself, its connection with M-theory, and the weak coupling orientifold picture. Starting from a GUT-like model in the orientifold picture, the construction of consistent F-theory 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
"General Semi Direct Gauge Mediation"
Alberto Mariotti (VUB)
Leuven – February 24, 2010
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
"Defects and renormalisation group flows"
Stefan Fredenhagen (AEI Potsdam)
Leuven – February 24, 2010
One-dimensional defect lines have become an important tool in studying two-dimensional 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
"A dynamical inconsistency of Hořava gravity"
Gustavo Lucena Gómez (ULB)
VUB/ULB – February 17, 2010
The dynamical consistency of the non-projectable 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 second-class, 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
"Higgsless models"
Roberto Casalbuoni (University of Florence)
VUB/ULB – February 17, 2010
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
"An emergent Fermi Liquid from a strongly coupled quantum critical point"
Koenraad Schalm (Universiteit Leiden)
Leuven – February 10, 2010
A central problem in quantum condensed matter physics is the critical theory governing the zero temperature quantum phase transition between strongly renormalized Fermi-liquids 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 Anti-de-Sitter/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 Fermi-liquid.
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 and gauged supergravity: the D=2 case"
Teake Nutma (Groningen)
Leuven – February 10, 2010
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
"M5-branes wrapped on Riemann surfaces"
Francesco Benini (Princeton)
VUB/ULB – December 16, 2009
I will review Gaiotto's construction of N=2 SCFTs via M5-branes wrapped on Riemann surfaces, including an alternative type IIB construction suitable to study their flavor symmetries, and net of new S-dualities 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 2d-4d correspondence with Toda theories.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 16, 2009 at 13:00
"Non-Gaussian constraints on excited states in effective field theories of inflation"
Jan Pieter van der Schaar (UvA)
VUB/ULB – December 16, 2009
Deviations from the Bunch-Davies vacuum during an inflationary period can leave a testable imprint on the higher-order correlations of the CMB and large scale structures in the Universe. After an introduction of non-Gaussian 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 non-Gaussian bispectrum in two cases of specific interest:
1) single-field inflation with a canonical kinetic term plus a specific higher derivative correction and
2) general single-field inflation in the limit of small sound speed. After projecting these results on the available observational templates, the enhanced levels of non-Gaussianity are shown to result in relatively strong constraints on deviations from the Bunch-Davies 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
"A light scalar from walking solutions in gauge-string duality"
Daniel Elander (Swansea U.)
Leuven – December 9, 2009
Recently, a class of solutions to the Type IIB system of Nc D5-branes 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
"Quantum aspects of black holes"
Joan Simon (University of Edinburgh)
Leuven – December 9, 2009
Place: Leuven, Celestijnenlaan 200D, room 05.34
Time: Wednesday, December 9, 2009 at 10:30
"Holographic Flavor Transport"
Andy O'Bannon (MPI Munich)
VUB/ULB – December 2, 2009
Gauge-gravity duality is an extremely useful tool for studying strongly-coupled gauge theories, and has many applications to real-world systems, such as the quark-gluon plasma and quantum critical points. It is especially useful for studying the hydrodynamics of strongly-coupled non-Abelian gauge theories. For example, gauge-gravity 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 strongly-coupled plasma. From the result for the conductivity, I will show how gauge-gravity duality captures a lot of real-world 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
"Large N duality beyond the genus expansion"
Sara Pasquetti (CERN)
VUB/ULB – December 2, 2009
In this talk we will study the nature of the non-perturbative corrections in gauge/strings dualities. We consider a toy model of gauge/string duality relating the Chern-Simons theory on lens spaces to the topological string on toric Calabi-Yau'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 non-trivial 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
"Stringy instanton calculus"
Marco Billò (Torino)
Leuven – November 25, 2009
In (supersymmetric) gauge theories realized on D-brane worlds, classes of non-perturbative corrections can be derived by taking into account the presence of D-brane instantons. Some of these latter correspond to the ordinary gauge theory instantons, other ones yield novel "stringy" or "exotic" non-perturbative effects, potentially of phenomenological relevance. To put on firm grounds the computation of the exotic contributions to the effective action, and to investigate their field-theoretic interpretation we focus first on an 8-dimensional example, the D(-1)/ D7 system in type I' theory. The gauge theory on the D7-brane 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
"A flavour superconductor from string theory"
Johanna Erdmenger (MPI München)
Leuven – November 25, 2009
We obtain a holographic superconductor model in which 1) the field theory dual is explicitly known; 2) there is a string-theoretical picture of the pairing mechanism. To achieve this, we consider thermal strongly-coupled N=2 Super Yang-Mills theory with fundamental matter at finite isospin chemical potential. Using gauge/gravity duality, ie. a probe of two flavour D7-branes 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 frequency-dependent 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
"N=2 Chern-Simons matter theories: RG flows and IR behavior"
Silvia Penati (Milano-Bicocca University)
VUB/ULB – November 18, 2009
Motivated by the AdS4/CFT3 correspondence, I consider two-level supersymmetric Chern-Simons 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
"Instabilities and new phases of higher-dimensional rotating black holes"
Pau Figueras (University of Durham)
VUB/ULB – November 18, 2009
It has been conjectured that higher-dimensional 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 Myers-Perry 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 Myers-Perry black holes with all the angular momenta equal. For this class of black holes, we have studied the explicit time-dependence 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
"Moduli fixing in asymmetric heterotic orbifold"
Cristina Timirgaziu (Liverpool)
VUB/ULB – November 4, 2009
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 semi-realistic 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
"Spontaneous partial supersymmetry breaking in supergravity"
Paul Smyth (Hamburg)
VUB/ULB – November 4, 2009
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
"Tensor Hierarchies and Supergravities"
Jelle Hartong (Bern U.)
Leuven – October 28, 2009
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 4-dimensional supergravities. After discussing the 4-dimensional case to some detail I will outline what happens in higher-dimensional 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
"Multi-Trace Deformations of AdS/CFT and Spherical D-branes"
Alice Bernamonti (Vrije Universiteit Brussel)
Leuven – October 28, 2009
It has been shown by Hertog and Horowitz that certain AdS boundary conditions allow non-singular 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 multi-trace 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 D-brane interpretation of the unbounded potential. In particular, I will show that the AdS boundary conditions of interest cause spherical D-branes to be pushed to the boundary of AdS, and that the corresponding potential agrees with the multi-trace deformation of the boundary field theory.
Place: Leuven, Celestijnenlaan 200D, room 05.34
Time: Wednesday, October 28, 2009 at 10:30
"Topology of gauge fields and anomalous baryon number non-conservation"
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – October 21, 2009
I will introduce topology of gauge fields responsible for baryon number violation in the Standard Model and describe physical mechanism behind this non-perturbative 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 tunneling-type 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
"Comments on Supersymmetry and Inflation"
Luis Alvarez-Gaumé (CERN)
VUB/ULB – October 21, 2009
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
"M2-branes, triple systems and superalgebras"
Jakob Palmkvist (ULB)
VUB/ULB – October 14, 2009
I will review the three-dimensional superconformal N=6 theories of ABJM type, and explain that the three-algebras used by Bagger and Lambert can be described as generalized Jordan triple systems. Using this description, I will show that simple three-algebras are in one-to-one 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
"Half BPS Supergravity Solutions and Superalgebras"
Darya Krym (KUL)
VUB/ULB – October 14, 2009
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, October 14, 2009 at 10:30
"Solvay chair in physics 2009: Lectures on inflation"
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – October 8, 2009
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, 16:00-18:00
"Solvay chair in physics 2009: Lectures on inflation"
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – October 7, 2009
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, 16:00-18:00
"Why not a NUT story ?"
François Dehouck (ULB)
Leuven – October 7, 2009
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 Taub-NUT 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
"Renormalization group in Lifshitz-type theories"
Marco Serone (SISSA)
Leuven – October 7, 2009
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 ∼ c2φ1-c2φ2 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 fine-tuned to extremely small values in the UV.
Place: Leuven, Celestijnenlaan 200E, room 01.207
Time: Wednesday, October 7, 2009 at 10:30
"Solvay chair in physics 2009:
Lectures on inflation"
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – October 6, 2009
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, 16:00-18:00
"Solvay chair in physics 2009:
Lectures on inflation"
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – October 5, 2009
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, 16:00-18:00
"Inaugural lecture of the 2009 Solvay chair in physics "
"Particle physics and cosmology: towards understanding the Universe "
Valery Rubakov (Institute for Nuclear Research, Moscow)
VUB/ULB – September 29, 2009
Knowledge gained so far in cosmology is to a large extent orthogonal to current knowledge in particle physics. There is matter and no anti-matter 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