Group seminars
Besides the joint ULB-VUB-KUL-UMons seminars, the group organizes local seminars.
Friday, February 24 2012, 14h00
Alexander Belavin
Instantons and 2d Coset CFT.
A few years a Alday,Gaiotto and Tachikawa dicovered a remarkable correspondence between $N=2$ SUSY gauge theory in $4$ dimensions and $2$-dimensional Conformal field theory. We consider the generalization this correspondence to the case 4-dimensional $N=2$ SUSY $SU(r)$ gauge theory on the $R_4/Z_p$ and Coset 2d Conformal field theory with the chiral algebra $ A{r,p}=frac{widehat{**mathfrak{gl}](n)_r}>{widehat{mathfrak{gl}}(n-p)_**r}$. The algebraic reason of the correspondence is the existence of a natural action of this chiral algebra on cohomologies of Instanton Moduli space. Basis of the cohomologies space consists of the torus fixed points (Nekrasov's instantons). From 2d point of view it is a special basis in the Algebra of Local Fields in the corresponding CFT. Structure constants of OPE in this basis are given by explicit and simple expressions. I describe the construction of such basis for case $ r=2 $, $p=2$ .
Campus Plaine, Room N0.6.10
Thursday, January 17 2012, 14h00
Juan Maldacena
Constraining theories with higher spin symmetry
We consider conformal field theories with exactly conserved
currents of spin s> 2. We show that such theories are essentially
free theories. This is an extension of the Coleman Mandula theorem to
the case of conformal field theories.
We also discuss the case where the higher spin symmetry is slightly broken.
Based on papers by JM and A. Zhiboedov, *arXiv:1112.1016& to
appear.
Campus Plaine, Solvay Room (5th floor, NO Building)
Monday, October 17 2011, 10h30
Frank Ferrari
Two Dimensional Quantum Gravity Revisited
I'll describe in elementary terms a new approach to the sum over Kähler metrics which provides in particular a rigorous definition of the quantum gravity path integral in two dimensions. The method relies on rather recent developments in complex geometry by Tian, Yau, Donaldson and others. If I have enough time, I'll also briefly talk about new gravitation effective actions (beyond the standard Liouville case) that show up naturally in this context.
Campus Plaine, Room NO.6.10 (Sixth floor, NO building)
Monday, September 12 2011, 10h30
Hamid R.Afshar
Holograms of Conformal Chern-Simons Gravity
We show that conformal Chern-Simons gravity in three dimensions has various holographic descriptions. They depend on the boundary conditions on the conformal equivalence class and the Weyl factor, even when the former is restricted to asymptotic Anti-deSitter behavior. For constant or fixed Weyl factor our results agree with a suitable scaling limit of topologically massive gravity results. For varying Weyl factor we find an enhancement of the asymptotic symmetry group, the details of which depend on certain choices. We focus on a particular example where an affine u(1) algebra related to holomorphic Weyl rescalings shifts one of the central charges by 1. The Weyl factor then behaves as a free chiral boson in the dual conformal field theory.
Campus Plaine, Salle des professeurs (Ninth floor, NO building)
Wednesday, September 07 2011, 14h00
Adam Schwimmer (Weizmann Institute of Science, Israel)
Trace Anomaly Matching and the a-Theorem
The a-Theorem gives a characterization of RG flows for unitary theories in d=4. We will discuss a proof of the theorem based on the matching of conformal anomalies and the special features of the dilaton effective action in spontaneously broken conformal theories.
Campus Plaine, Solvay Room (Fifth floor, NO building)
Thursday, June 30 2011, 14h00
Bernard L. Julia (Ecole Normale Supérieure)
The supermagic triangle is 30
TBA
Campus Plaine, Salle des professeurs (Ninth floor, NO building)
Thursday, June 30 2011, 11h00
Eric A. Bergshoeff (University of Groningen)
New Results on Supersymmetric Solitons in String Theory
We probe doubled geometry with dual fundamental branes, i.e. solitons. Restricting ourselves first to solitonic branes with more than two transverse directions we find that the doubled geometry requires an effective wrapping rule for the solitonic branes which is dual to the wrapping rule for fundamental branes. This dual wrapping rule can be understood by the presence of Kaluza-Klein monopoles. Extending our analysis to supersymmetric solitonic branes with less than or equal to two transverse directions we show that such solitons are precisely obtained by applying the same dual wrapping rule to these cases as well. This extended wrapping rule can not be explained by the standard Kaluza-Klein monopole alone. Instead, it suggests the existence of a class of generalized Kaluza-Klein monopoles in ten-dimensional string theory.
Campus Plaine, Salle des professeurs (Ninth floor, NO building)
Wednesday, June 1 2011, 14h00
Xavier Bekaert (Tours U., CNRS)
Effective action in a higher-spin background
The regularised effective action, obtained after integrating out a scalar field with the most general (quasi-)local quadratic action, is computed perturbatively in the external fields. The latter fields are interpreted as an infinite tower of background higher-spin gauge fields. The non-Abelian group of higher-spin symmetries and anomalies, as well as the structure of the various (divergent or finite) terms, is determined. The relation of these results with the holographic correspondence and a generalized induced gravity programme (à la Sakharov) is discussed.
Campus Plaine, Solvay Room (Fifth floor, NO building)
Tuesday, May 31 2011, 11h00
Alan Garbarz (University of Buenos Aires)
Topics on 3d gravity and AdS/CFT
In this talk we will discuss some aspects of three dimensional gravity and the recent attempts to construct its quantum version in a consistent manner via AdS/CFT correspondence. We will start reviewing seminal results in the field, such as Brown-Henneaux´s work on asymptotic symmetries, which will play a main role in the discussion. The main idea of Witten´s work of 2007 will also be commented due to its importance in triggering the recent study of others (than GR) gravitational theories in three dimensions. Among these theories, we will discuss the so-called Chiral Gravity, its cousin dubbed Log Gravity, and the more recent New Massive Gravity. These theories are intended to give alternatives for a possible quantum theory of gravity in three dimensions, with notable differences in comparison with GR, such as novel black holes solutions and deformed AdS asymptotics. In addition, possible physically sensible contributions to the partition function will be mentioned, like particle-like singularities and space-times with torsion.
Campus Plaine, Room NO.6. 10 (Sixth floor, NO building)
Monday, May 16 2011, 11h00
Dmitry Melnikov (Tel Aviv University)
"High Density Holographic Baryons"
Large N hadronic matter must possess a nuclear crystal phase. In my talk I will discuss a holographic realization of nuclear crystals. In particular I will be interested in the behavior of the crystals at very high densities, where the phase transition to a quark liquid phase is expected.
Campus Plaine, Solvay Room (Fifth floor, NO building)
Monday, April 11 2011, 14h00
Oscar Bedoya (Sao Paulo)
"Superstring Sigma Models Computation Using the Pure Spinor Formalism"
In this talk I will show how using one-loop computations in the Superstring Sigma model with pure spinors, one can extract useful information about the space-time. I will consider three examples: The space-time equations of motion for the the type II Superstring, the Yang-Mills Chern Simons corrections, and finally, the quantum current algebra for the superstring in the $AdS_5 \times S^5$ background.
Campus Plaine, Solvay Room (Fifth floor, NO building)
Thursday, February 17 2011, 14h00
Rakibur Rahman (Scuola Normale Superiore)
"String Theory and The Velo-Zwanziger Problem"
The Velo-Zwanziger problem is the loss of (causal) propagation of a charged massive field with spin > 1, when minimally coupled to a constant electromagnetic background. String theory, originally proposed as a theory of massive high-spin particles, should spell out appropriate non-minimal terms to give a consistent description of such a system. We show that while string theory does achieve this feat, only the leading Regge trajectory fields can be exposed in isolation. We comment on the roles of the critical dimension and of the gyromagnetic ratio, and prescribe some consistent dimensional reduction that can produce interesting models.
Campus Plaine, Room NO.6. 10 (Sixth floor, building NO)
Click here for the old group seminars webpage.