Theoretical High Energy Particle Physics Group

String Theory Seminars

Place: Potter Room (first floor, Pavilion B of the CMS)
Time: Thursdays, 1pm
Organiser: Dr Hadi Godazgar, Dr Joao Gomes

Michaelmas 2014

09-Oct-2014: Exotic Branes and 3D Supergravity

Daniel Mayerson (University of Amsterdam) [Transparencies]
Abstract: String theory has been known for quite a while to contain non-perturbative objects called D-branes in addition to the fundamental strings the theory is named after. However, fairly recently, new types of membranes in string theory are being studied with increasing interest: the so-called "exotic branes" (also known by other names). These exotic branes have the interesting feature that their spacetime is multi-valued or non-geometric; this means that when you travel in a circle around the brane, the resulting spacetime looks different from that which you started out with! It is of considerable interest to study and classify the possible types of such exotic branes that can exist in string theory. To study them, we can work in a 3D theory (of maximal supergravity), where the exotic branes are just point particles. In this theory, we can at least classify the supersymmetric point particles, thereby gaining insight into what kind of supersymmetric exotic branes exist in string theory. This problem reduces to that of classifying nilpotent orbits associated with the U-duality group (E_8), for which various mathematical results are known. It can be shown that the only allowed supersymmetric configurations are 1/2, 1/4, 1/8, and 1/16 BPS, and their respective nilpotent orbits can be given explicitly. On the other hand, it turns out exceedingly difficult to translate this classification into a simple criterion for supersymmetry in terms of the non-Abelian (monodromy) charges of the objects.

16-Oct-2014: Integrable deformations of AdS3 x S3 x M4 strings

Ben Hoare (Humboldt-University of Berlin) [Transparencies]
Abstract: In this talk we will explore integrable deformations of the GxG/G_0 supercoset sigma model that plays a role in the Green-Schwarz formulation of superstrings on AdS3 x S3 x T4 (G = PSU(1,1|2)) and AdS3 x S3 x S3 x S1 (G = D(2,1;α)). After reviewing the single parameter deformation of Delduc, Magro and Vicedo, which treats the two copies of G symmetrically, the main focus of the talk will be the construction of an asymmetric two-parameter deformation based on Κlimčík's bi-Yang-Baxter sigma model. Some evidence will also be presented for the existence of a three-parameter deformation. Various interesting limits (including the squashed three-sphere, the Pohlmeyer-reduced theory and the mirror model) of the corresponding deformed metrics will be analyzed and the issue of whether these models describe deformations of superstrings will be briefly discussed.

23-Oct-2014: TBA

Henning Samtleben (ENS Lyon) [Transparencies]

30-Oct-2014: TBA

Nima Doroud (DAMTP-Cambridge) [Transparencies]

06-Nov-2014: TBA

Heng-Yu Chen (National Taiwan University) [Transparencies]

13-Nov-2014: TBA

James Lucietti (University of Edinburgh) [Transparencies]

20-Nov-2014: TBA

Ted Erler (LMU-Munich) [Transparencies]

27-Nov-2014: TBA

Michael Ferlaino (Swansea University) [Transparencies]

04-Dec-2014: TBA

Glenn Barnich (ULB- Brussels) [Transparencies]

Easter 2014

24-Apr-2014:Brane deformations in supergravity

Vasilis Niarchos (University of Crete) [Transparencies]
Abstract:I will present recent work on the physics of long-wavelength supersymmetric deformations of brane solutions in supergravity. We will see how familiar concepts from D-brane theory, like the Dirac-Born-Infeld action and the kappa-symmetry condition, arise directly from the supergravity equations and will discuss their implications on the SUGRA /DBI correspondence. As a concrete example, we will consider the case of M5 branes in eleven-dimensional supergravity.

01-May-2014: Resurgent Analysis in Quantum Theories: Perturbative Theory and Beyond

Ines Aniceto (Lisbon, IST Maths) [Transparencies]
Abstract:In order to study the weakly coupled regime of some given quantum theory we often make use of perturbative expansions of the physical quantities of interest. But such expansions are often divergent, with zero radius of convergence, and defined only as asymptotic series. In fact, this divergence is connected to the existence of nonperturbative contributions, i.e. instanton effects that cannot be simply captured by a perturbative analysis. The theory of resurgence is a mathematical tool which allows us to effectively study this connection and its consequences. Moreover, it allows us to construct a full non-perturbative solution from perturbative data. In this talk, I will review the essential role of resurgence theory in the description of the analytic solution behind the asymptotic series. I will then relate resurgence to the so-called Stokes phenomena and phase transitions using a simple example, and will further discuss some major applications of this construction.

08-May-2014: The superconformal index of the (2,0) theory with defects

Mathew Bullimore (Perimeter) [Transparencies]
Abstract:String theory predicts the existence of a class of interacting superconformal field theories in six dimensions which arise on the world-volume of coincident M5 branes. There are important defect operators in these theories corresponding to intersecting M2 and M5 branes. I will explain how to compute the superconformal index in the presence of such defects using five-dimensional supersymmetric gauge theory and show that they are in one-to-one correspondence with the characters of irreducible representations of a class of chiral algebras.

15-May-2014: Conformal Partial Waves, the building blocks of the Conformal Bootstrap

Hugh Osborn (DAMTP) [Transparencies]

22-May-2014: Hyperkahler Sigma Model and Field Theory on Gibbons-Hawking Spaces

Anindya Dey (U Texas) [Transparencies]
Abstract:We will introduce a deformed version of the 3d hyperkahler sigma model which arises from the compactification of d=4,N=2 gauge theories on a Gibbons-Hawking space. After discussing extensions of the relevant hyperkahler identities from the standard story, we will derive the condition for which the deformed sigma model preserves 4 out of the 8 supercharges. Using supersymmetry considerations, we will also demonstrate that the contribution of the NUT center to the sigma model path integral is a holomorphic section of a certain holomorphic line bundle over the hyperkahler target. As a concrete example, we will discuss the case where the original 4d theory is a U(1) super Yang-Mills and show that the NUT center contribution in this case is the Jacobi theta function.


Guido Festuccia (NBI) [Transparencies]

05-Jun-2014: TBA

Paul Heslop (Durham University) [Transparencies]

12-Jun-2014: TBA

Diego Hofman (UVA) [Transparencies]

19-Jun-2014: TBA

TBC [Transparencies]

Past Seminars

  • 2014: - -
  • 2013: - -
  • 2012: - -
  • 2011: - -
  • 2010: - -
  • 2009: - -
  • 2008: - -
  • 2007: - -