Past seminars

Academic year: September 2003 - September 2004

Closed Timelike Curves are present in a number of solutions of Classical General Relativity and are, in general, regarded as pathological. It was suggested by Hawking in the early 90s that the `Chronology Protection Mechanism' should involve quantum effects. It becomes therefore interesting to explore the nature of CTC's in a framework of quantum gravity like string theory. The discovery of supersymmetric Godel type universes in string theory which are T-dual to pp-waves and the existence of supersymmetric rotating black holes (which have Closed Timelike Curves) possessing a CFT description motivated several suggestions on how string theory might cope with Closed Timelike Curves. In this seminar I will review some of these recent suggestions.

Place:  K.U. Leuven, Celestijnenlaan 200 D, D06.32
Time:   Monday, July 12, 2004 at 10:30

We will study the paper by Blumenhagen, Braun, Kors & Lust (hep-th/0206038) about orientifolds with intersecting branes. Attention will be paid to the topology of the orbifold limit models.

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, June 16, 2004 at 10:30

Place:  ULB, Solvay room
Time:   Wednesday, June 09, 2004 at 10:30

You can find further info on the website.

Place:  K.U. Leuven, Celestijnenlaan 200C. Auditorium A
Time:   Friday, June 04, 2004, 10:00-17:30

Semiclassical strings have been recently used to study the AdS/CFT duality beyond the supergravity approximation. I consider the possibility to apply the same approach to study the IR sector of supergravity backgrounds dual to confining gauge theories with (softly broken) N=1 supersymmetry. In particular, folded and circular string configurations are considered, which correspond to massive multicharged hadrons in the dual confining gauge theory. Their classical energy/charge relations are shown, as well as the one-loop sigma model corrections for the case of circular strings. Differently from the AdS/CFT duality, these corrections are not subleading in the limit of infinite charge.

Place:  Leuven, Celestijnenlaan 200D, D06.32
Time:   Wednesday, June 02, 2004 at 13:30

We will investigate the possibility of a phase transition from a rotating black hole in d=5 to the black ring found by Emparan and Reall (which constitutes the first known example of non-uniqueness of black holes in asymptotycally flat spacetime). We will demonstrate that, by throwing test particles into the black hole (in a generic situation, i.e. not just at extremality), one can ``oversipin it'' beyond its extremal limit, creating a naked singularity. Moreover, with such an experiment one can even violate the Hawking area theorem when the rotation parameter of the black hole exceeds a certain critical value. Both facts could be taken as a proof of instability of the high rotation regime of the BH, but we argue that the possibility of violating the second law may be have a more problematic interpretation. Then we will study the local thermodynamic behaviour of the black hole and black ring phases (for which we explicitly derive a fundamental relation), finding critical behaviour precisely in the region of coexistence of both phases. Finally, we will report on the properties of the curvature of the ``information metric'' of the thermodynamic state space, finding also critical (although non equivalent) behaviour in the same region.

Place:  Leuven, Celestijnenlaan 200D, D06.32
Time:   Wednesday, June 02, 2004 at 10:30

Place:  VUB, Oefenplein, building E, E.3.06
Time:   Wednesday, May 19, 2004 at 13:30
Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, May 19, 2004 at 10:30
Place:  ULB, Campus Plaine, Salle Solvay, building NO, 5th floor
Time:   Wednesday, May 12, 2004

Maxim will explain a first quantized particle model that allows to compactly generate the Fronsdal action for all massless higher spin fields. Giulio will then explain the relation of this model with the tensionless limit of string (field) theory.

Place:  ULB, Campus Plaine, building NO, room 2NO.6.010
Time:   Monday, May 10, 2004 at 11:00

Place:  Leuven, Celestijnenlaan 200D, D05.11
Time:   Wednesday, May 05, 2004 at 13:30

Note: overlap with the discussion group on String Field Theory.

Place:  Leuven, Celestijnenlaan 200C, C01.E
Time:   Wednesday, May 05, 2004 at 10:30

An elementary introduction to higher spin gauge theories in order to prepare for the workshop.

Note: overlap with the discussion group on overextensions.

Place:  Leuven, Celestijnenlaan 200D, D05.11
Time:   Wednesday, May 05, 2004 at 10:30

I will discuss the geometry of supergravity backgrounds of the Freund-Rubin type and discuss their Kaluza-Klein reductions and associated discrete quotients, paying particular attention to the fate of supersymmetry.

Place:  VUB, Oefenplein, building E, E.3.06
Time:   Wednesday, April 28, 2004 at 13:30

Today: "Brane recombination, a picture for symmetry breaking" by Joke Adam

We will discuss some ideas about the Higgs mechanism in intersecting brane models. Brane recombination, as mentioned in the paper of D. Cremades, L.E. Ibanez and F. Marchesano (hep-th/0203160), provides us an interpretation of this Standard Model feature in the language of branes.

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, April 28, 2004 at 10:30

I first remind about general aspects of instantons in field theory. Then I discuss non-perturbative effects in string theory and supergravity, and show how they contribute to low-energy effective actions. As an example, I will discuss fivebrane instantons in type II strings compactified on Calabi-Yau manifolds.

References on non-perturbative string theory:

    * Becker, Becker and Strominger: hep-th/9507158
    * Harvey and Moore: hep-th/9907026

Background material (lecture notes on nonperturbative string theory):

    * E. Kiritsis: hep-th/9708130, hep-th/9906018

Some more detailed references that I will mention:

    * Gibbons, Green and Perry: hep-th/9511080
    * Theis and Vandoren: hep-th/0208145
    * Davidse, de Vroome, Theis and Vandoren: hep-th/0309220

Place:  Leuven, Celestijnenlaan 200D, D05.11 (part I)
            VUB, Oefenplein, building G, 1G.003 (part II)
Time:   Wednesday, March 03, 2004 at 13:30
            Wednesday, April 21, 2004 at 10:30

Guilio has volunteered to further elucidate section 5 of the Giddings-Martinec paper on the ghost path integral and to conclude his review on the relation between the first and second quantized approaches.

Place:  Leuven, Celestijnenlaan 200D, D05.34
Time:   Wednesday, April 14, 2004 at 10:30

It will be a pedagogical introduction to the concept of realising Kac-Moody type symmetries via non-linear realisations. This concept is presented for various different Kac-Moody algebras and shown to be in correspondence to known T-dualities and some simple vacuum solutions of supergravity theories.

Place:  VUB, Oefenplein, building E, E.3.06
Time:   Wednesday, April 07, 2004 at 13:30

Place:   VUB, Oefenplein, building G, 1G.003
Time:    Wednesday, April 07, 2004 at 10:30

I will argue that a mirror symmetry exists for manifolds of SU(3) structure. I will first explain what this is supposed to mean, pedagogically introducing all the concepts needed. I will then present an approach using T-duality along three directions (à la SYZ) when this is allowed. The results of the computation will be expressed in an appropriate basis for intrinsic torsion and shown to have a natural interpretation in terms of Hitchin's generalized complex geometry. This formalism, recently advocated by Hitchin, puts T and T* on equal footing. I will give a brief introduction to it and then use it to conjecture a map for intrinsic torsion of mirror pairs in the general (non T3-fibred) case.

Place:  ULB, Campus Plaine, Salle Solvay, building NO, 5th floor
Time:   Wednesday, March 31, 2004 at 13:30

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, March 31, 2004 at 10:30

Guilio Bonelli (ULB) will explain some aspects of the relationship between S-matrix elements computed from te SFT and the amplitudes computed in CFT. Suggested reading: ref 75-77 of the Taylor-Zwiebach review.

Note: Parallel with the discussion group on intersecting brane models.

Place:  ULB, Campus Plaine, room 2.06.111
Time:   Wednesday, March 31, 2004 at 10:30

The features of intersecting extremal branes suggest the existence of a much larger symmetry, namely the `very-extended' Kac-Moody algebras G+++. This motivates the construction of explicit non-linear realisations of all simple G+++, which hopefully contain new degrees of freedom such as those encountered in string theories. They are defined without a priori reference to space-time and are proposed as substitutes for original field theoretic models of gravity, forms and dilatons. From the G+++ invariant theories, all algebraic properties of intersecting extremal branes are recovered from exact solutions, and there are indications that space-time is hidden in the infinite symmetry structure. The transformation properties of the exact solutions, which possibly induce new solutions foreign to conventional theories, put into evidence the general group-theoretical origin of "orthodox" and "exotic" "dualities" for all G+++. These dualities apparently do not require an underlying string theory.

Place:  Leuven, Celestijnenlaan 200D, D05.11
Time:   Wednesday, March 24, 2004 at 13:30

Theories of gravity coupled to forms and dilatons may admit as solutions zero binding energy configurations of intersecting closed extremal branes. In such configurations, some branes may open on host closed branes. Properties of extremal branes reveal symmetries of the underlying theory which are well known in M-theory but transcend supersymmetry. From these properties it is possible to reconstruct all actions, comprising in particular pure gravity in D dimensions, the bosonic effective actions of M-theory and of the bosonic string, which upon dimensional reduction to three dimensions are invariant under the maximally non-compact simple simply laced Lie groups G.

Place:  Leuven, Celestijnenlaan 200D, D05.11
Time:   Wednesday, March 24, 2004 at 10:30

Giant gravitons in AdS_m x S^n spacetimes provide a realization of the stringy exclusion principle. These solutions have been studied in the literature in terms of spherical branes with angular momentum, which expand in the spherical part of the geometry. This is the so called macroscopical description. The aim of this talk is to study these solutions microscopically in terms of graviton degrees of freedom. We will show that systems of coincident gravitons in AdS_m x S^n can expand into higher dimensional spherical branes by the analogous of Myers dielectric effect for coincident D-branes. We will show that for a large number of gravitons the results are in perfect agreement with the macroscopical description given in the literature.

Place:  VUB, Oefenplein, building E, E.3.06
Time:   Wednesday, March 17, 2004 at 13:30

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, March 17, 2004 at 10:30

Note: Parallel with the discussion group on flux compactifications.

Place:  ULB, Campus Plaine, building NO, 2.N.6.110
Time:   Wednesday, March 17, 2004 at 10:30

The E_11 conjecture asserts that M-theory has a huge, non-linearly realized symmetry, parametrized by the coset E_11/H_11. The signature of space-time is encoded in the denominator sub-algebra H_11, and indirectly implies which real form of this algebra one is supposed to use. Even then, a particular choice of real form does not specify the space-time signature uniquely, but multiple theories are possible by choosing various decompositions with respect to a "gravitational sub-algebra". We discuss the relations with time-like T-dualities, give a sketch on how a full classification is obtained, and give various results for the E-type duality algebra's relevant for dimensionally reduced maximal supergravities.

Place:  ULB, Campus Plaine, Salle Solvay, building NO, 5th floor
Time:   Wednesday, March 10, 2004 at 13:30

I will show how to construct some Eulidean supergravity solutions with multiple boundaries, and discuss the puzzling features of these configurations from the point of view of AdS/CFT.

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, March 10, 2004 at 10:30

We will continue the intersecting brane world lectures as a working group as originally planned. The participants are asked to read the paper hep-th/0105155 (also related to the paper hep-th/0107138).

Place:  Leuven, Celestijnenlaan 200D, D05.11
Time:   Wednesday, March 03, 2004 at 10:30

We will introduce several papers for continuing the intersecting brane world lectures as a working group as originally planned. These papers include the topics:

    * chiral spectrum of IB on a Calabi-Yau;
    * gauge coupling unification;
    * SUSY orientifolds;
    * proton decay;
    * orientifolds of Gepner Models;
    * Yukawa couplings from intersecting branes;
    * getting the Standard Model from intersecting branes;
    * Higgs mechanism in IB's.

Place:  VUB, Oefenplein, building E, E.3.06
Time:   Wednesday, February 25, 2004 at 13:30

Note: Parallel with the discussion group on String Field Theory.

There will be a discussion about the further course of the group.

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, February 25, 2004 at 10:30

Note: Parallel with the discussion group on flux compactifications.

Place:  ULB, Campus Plaine, room TBA
Time:   Wednesday, February 25, 2004 at 10:30

I will introduce a string theory model with a big crunch/big bang singularity and discuss globally defined fluctuation spectra.

Place:  ULB, Campus Plaine, Salle Solvay, building NO, 5th floor
Time:   Wednesday, February 18, 2004 at 13:30

Introduction to the seminar of the afternoon.
Ideally (but I may not have enough time for everything), I'd like to

    * go through some basics of Friedmann-Robertson-Walker cosmology
    * say a few words about the Cosmic Microwave Background and its anisotropies
    * discuss fluctuations in (a simplified version of) the inflationary universe.

A good entry point to the literature is the recent review of Trodden and Carroll, astro-ph/0401547. A fun place to learn about the CMB (at various level is) Wayne Hu's website.

Place:  VUB, Oefenplein, building G, 1G.003
Time:   Wednesday, February 18, 2004 at 10:30

Supersymmetric solutions of string theory in the presence of fluxes play a key role for the gauge/gravity correspondence, for solving the moduli problem and also for stabilizing the free parameters of intersecting brane-world scenarios. We will show how the tool of group structures can be used to classify and construct such solutions. We will also discuss some consequences for the 4-dimensional effective theories derived in this way.

Place:  Leuven, Celestijnenlaan 200D, D06.34
Time:   Wednesday, February 11, 2004 at 13:30

Note: Parallel with the discussion group on flux compactifications.

Place:  Leuven, Celestijnenlaan 200, TBA
Time:   Wednesday, February 11, 2004 at 10:30

With invited guest Gianguido Dall'Agata. Question for Gianguido can be send to Jos Gheerardyn. Note: Parallel with the discussion group on String Field Theory.

Place:  Leuven, Celestijnenlaan 200, TBA
Time:   Wednesday, February 11, 2004 at 10:30

Place:  ULB, Campus Plaine, building NO, 2.NO.906
Time:   Wednesday, February 04, 2004 at 13:30
See http://www1.phys.uu.nl/drstp/Postgr.courses/hef.htm.

No seminars on Thursday 22/01/2004 and Thursday 29/01/2004

Time:   Monday, January 19, 2004

You can find further info on http://homepages.ulb.ac.be/~mfairbai/pai.html/

Place:  ULB, Campus Plaine, TBA
Time:   Monday, January 19, 2004

See http://sonia.ecm.ub.es/~school/.

No seminars on Thursday 15/01/2004.

Place:  Barcelona !
Time:   Monday, January 12, 2004

Penrose's cosmic censorship hypothesis states that under reasonable conditions, smooth initial data do not produce naked singularities. I show that cosmic censorship does not hold in asymptotically anti de Sitter spacetimes, for certain matter theories, including N=8 gauged supergravity in both four and five dimensions. I describe how this result provides a new approach to the study of cosmological singularities, using the dual field description of the nakedly singular solutions.

Place:  KULeuven, Celestijnenlaan 200D, building D, room 06.32
Time:   Wednesday, January 7, 2004 at 13:30

Note: Parallel with the discussion group on flux compactifications.

Place:  KULeuven, Celestijnenlaan 200D, building D, room 06.32
Time:   Wednesday, January 7, 2004 at 10:30

Note: Parallel with the discussion group on String Field Theory.

Place:  KULeuven, Celestijnenlaan 200D, building D, room TBA
Time:   Wednesday, January 7, 2004 at 10:30

See http://itf.fys.kuleuven.ac.be/itf/html/edu_courses.php?lang=en.

Place:  KULeuven, Celestijnenlaan 200D, building D, room 06.34
Time:   Monday, January 5, 2004 at 09:00

Supersymmetric solutions of 11-dimensional supergravity can be classified according to the holonomy of the supercovariant derivative arising in the Killing spinor condition. The holonomy must be contained in SL(32,R). The holonomies of solutions with flux are discussed and examples are analysed. In extending to M-theory, account has to be taken of the phenomenon of `supersymmetry without supersymmetry'. It is argued that including the fermionic degrees of freedom in M-theory requires a formulation with an enhanced local symmetry and which may be as large as SL(32,R), analogous to the need for local Lorentz symmetry in coupling spinors to gravity.

Based on hep-th/0305039.

Place:  ULB, Campus Plaine, Forum C
Time:   Thursday, December 18, 2003 at 13:30

A systematic algorithm of deriving exact time-dependent solutions of E_8(8)/SO(16) sigma-model in D=3 is presented. The solutions are classified by non-compact subalgebras of E_8(8). Their higher-dimensional physical interpretation (oxidation) depends on the classification of different embeddings of subalgebras, that fall into orbits of the Weyl group of E_8(8). In the same orbit there are representatives, that provide realizations of the billiard phenomenon in D=10 in presence of S--branes, and also representatives, corresponding to exact Bianchi type homogeneous cosmologies in D=4.

Place:  VUB, Oefenplein, building G, room G021
Time:   Thursday, December 18, 2003 at 10:30

An overview of the connection between random matrix models and supersymmetric gauge theories (found by Dijkgraaf and Vafa) is given. We focus on N=2 supersymmetry although most results apply to N=1 as well. Particular emphasis is put on subtleties which arise in vacua with Sp gauge symmetry.

Place:  ULB, Campus Plaine, Forum C
Time:   Thursday, December 11, 2003 at 13:30

Note: Parallel with the discussion group on String Field Theory.

Place:  ULB, Campus Plaine, 2.N.6.110
Time:   Thursday, December 11, 2003 at 10:30

Note: Parallel with the discussion group on flux compactifications.

Place:  ULB, Campus Plaine, 2.O.6.111
Time:   Thursday, December 11, 2003 at 10:30

We first describe how the formalism of G-structures can be applied to string compactifications. Then we discuss how to find explicit examples of backgrounds with N=1 supersymmetry.

Place:  ULB, Campus Plaine, Forum B
Time:   Thursday, December 4, 2003 at 13:30

Place:  VUB, Oefenplein, building G, room G021
Time:   Thursday, December 4, 2003 at 10:30

We consider D=4 accelerating cosmologies supported by a metric and N scalars for the case that the scalar potential is given by a single exponential. We make a systematic investigation of the accelerating phases of the different cosmologies. We consider the M-theory origin of a large class of solutions thereby emphasizing the connection with S--branes and group manifold reductions.

Place:  ULB, Campus Plaine, Forum C
Time:   Thursday, November 27, 2003 at 13:30

Note: Parallel with the discussion group on flux compactifications.

Place:  ULB, Campus Plaine, 2.O.6.111
Time:   Thursday, November 27, 2003 at 10:30

Note: Parallel with the discussion group on String Field Theory.

Place:  ULB, Campus Plaine, 2.N.6.110
Time:   Thursday, November 27, 2003 at 10:30

I will discuss non-supersymmetric large N "orientifold field theories". Specifically, I will discuss a gauge theory with a Dirac fermion in the anti-symmetric tensor representation. At large N and in a large part of its bosonic sector, this theory is non-perturbatively equivalent to N=1 SYM, so that exact results established in the latter (parent) theory also hold in the daughter orientifold theory. In particular, the non-supersymmetric theory has an exactly calculable bifermion condensate, exactly degenerate parity doublets, and a vanishing cosmological constant (all this to leading order in 1/N). Applications for (one flavor) QCD will be discussed as well.

Place:  Leuven, Celestijnenlaan 200G, building G, room G00.10
Time:   Thursday, November 20, 2003 at 10:30

In this lecture, I will give a detailed introduction on the Gimon-Polchinski-Model which historically was the first orientifold model using the picture of D-branes. Actually, this model has been found by Sagnotti et al. much earlier, but did not receive much attention at that time.

The Gimon-Polchinski-Model is phenomenologically not interesting, but ideal to understand some of the fundamental properties of orientifolds. It suffices as a toy model.

For preparation, the original paper hep-th/9601038 can be read, but this is not necessary because all important ingredients will be covered within the lecture.

Place:  Leuven, Celestijnenlaan 200D, building D, room D06.34
Time:   Thursday, November 13, 2003 at 13:30

Note: Parallel with the discussion group on String Field Theory.

Place:  Leuven, Celestijnenlaan 200B, building B, room B02.16
Time:   Thursday, November 13, 2003 at 10:30

Note: Parallel with the discussion group on flux compactifications.

Place:  Leuven, Celestijnenlaan 200?
Time:   Thursday, November 13, 2003 at 10:30

Time:   Thursday, November 6, 2003 at 10:30

The aim of my (possibly series of) lecture(s) is to explain how one can use boundary states in rational CFT to construct intersecting brane worlds. Before I come to this point, I will review the following concepts: classical and quantum CFT, representation theory of (extended) Virasoro algebras, modular invariance. All these concepts will be illustrated by a simple example, the free boson. Next (and probably next week) I will review boundary states, the Cardy solution and possible generalizations. Finally I will explain how all these ideas can be combined to construct tadpole free string theories with low energy gauge theories and chiral fermions.

Recommended reading material:

Place:  ULB, Campus Plaine, Forum C
Time:   Thursday, October 30, 2003 at 13:30
            Thursday, November 6, 2003 at 13:30

Note: Parallel with the discussion group on flux compactifications.

Place:  ULB, Campus Plaine, 2 N7 110
Time:   Thursday, October 30, 2003 at 10:30

Note: Parallel with the discussion group on String Field Theory.

Place:  ULB, Campus Plaine, 2 N6 110
Time:   Thursday, October 30, 2003 at 10:30

Place:  KULeuven, Celestijnenlaan 200D, D05.34
Time:   Thursday, October 23, 2003 at 13:30
Place:  KULeuven, Celestijnenlaan 200B, B02.16
Time:   Thursday, October 23, 2003 at 10:30

In their very well-known papers, Seiberg and Witten found the effective low-energy lagrangian for N=2 4D SYM theory. We are playing the following game:

   1. Make a dimensional reduction of the original theory to 3, 2, or 1 dimensions.
   2. Evaluate the effective lagrangian in such a low-dimensional descendant of the theory.

The results are rather rich and nontrivial:

1. In the quantum-mechanical limit, we obtain a nonstandard "symplectic" sigma model with 2 (if starting from N=1 4D theory) or 4 (in the N=2 case) complex supercharges. The target space has dimension 3r or 5r (r is the rank of the group) and is neither Kahlerian nor hyper-Kahlerian.
2. For D=2, we obtain a standard Kahlerian sigma model in the N=1 case and a so called twisted N=4 sigma model in the N=2 case.
3. For D=3, it is a hyper-Kahlerian sigma model associated with the moduli space of a system of BPS monopoles. We generalize previously known results for unitary groups to the case of any gauge group.

This is a mini-review based on the works hep-th/0301230, hep-th/0209187, hep-th/0201048 and previous papers.

Place:  ULB, Campus Plaine, Forum C
Time:   Thursday, October 16, 2003 at 13:30

Place:   ULB, Campus Plaine, Forum A
Time:    Thursday, October 16, 2003 at 11:00

See http://web.iihe.ac.be/colloquium/default.htm.

Place:   VUB, Campus Oefenplein, Aula QD
Time:    Thursday, October 09, 2003, 09:00-19:00

This first meeting of the year will be devoted to a discussion session. During this, each of us/you will briefly present themselves emphasising their current scientific interests. Furthermore, we would like to get suggestions from you all concerning topics/speakers/format/....

Place:  Physics building K.U.Leuven (Celestijnenlaan 200D), room 06.34
Time:   Thursday, October 02, 2003 at 10:30
            Thursday, October 02, 2003 at 13:30

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