# Past String Theory Seminar

26 May 2014
12:00
Lara Anderson
Abstract
<em>We systematically analyze a broad class of dual heterotic and F-theory models that give four-dimensional supergravity theories, and compare the geometric constraints on the two sides of the duality. In this talk I will show that F-theory gives new insight into the conditions under which heterotic vector bundles can be constructed. We show that in many cases the F-theory geometry imposes a constraint on the extent to which the gauge group can be enhanced, corresponding to limits on the way in which the heterotic bundle can decompose. We explicitly construct all dual F-theory/heterotic pairs in the class under consideration where the common twofold base surface is toric, and give both toric and non-toric examples of the general results. Finally, we provide evidence for important new aspects of G-flux in four-dimensional compactifications.</em>
• String Theory Seminar
19 May 2014
12:00
Abstract
<em> 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.</em>
• String Theory Seminar
12 May 2014
12:00
Christoph Seig
Abstract
<em>The gamma_i-deformed N=4 SYM was proposed as the conformal field theory in a non-supersymmetric deformation of the AdS/CFT correspondence. As we have shown, conformal invariance is, however, broken in this theory by running double-trace couplings. Although these couplings are apparently suppressed in 't Hooft's planar limit, they give rise to finite size corrections in the planar spectrum. In particular, they should be considered in the integrability-based formulation of the planar spectral problem. In the talk, I will explain our results in detail and also discuss possible implications for the conjectured integrability-based approach.</em>
• String Theory Seminar
5 May 2014
12:00
Mathew Bullimore
Abstract
<em>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 non-local 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 operators using five-dimensional supersymmetric gauge theory. The answers are in 1-1 correspondence with characters of representations of a class of chiral algebras’. I will discuss potential applications of this result for bootstrapping correlation functions.</em>
• String Theory Seminar
28 April 2014
12:00
Xenia de la Ossa
Abstract
<em>We describe the tangent space to the moduli space of heterotic string theory compactifications which preserve N=1 supersymmetry in four dimensions, that is, the infinitesimal parameter space of the Strominger system. We establish that if we promote a connection on TX to a field, the moduli space corresponds to deformations of a holomorphic structure \bar{D} on a bundle Q. The bundle Q is constructed as an extension by the cotangent bundle T^*X of the bundle E= End(V) \oplus End(TX) \oplus TX with an extension class {\cal H} which precisely enforces the anomaly cancelation condition. The deformations corresponding to the bundle E are simultaneous deformations of the holomorphic structures on the poly-stable bundles V and TX together with those of the complex structure of X. We discuss the fact that the `moduli'' corresponding to End(TX) cannot be physical, but are however needed in our mathematical structure to be able to enforce the anomaly cancelation condition. This is work done in collaboration with Eirik Svanes.</em>
• String Theory Seminar
10 March 2014
12:00
James Drummond
Abstract
<em> We describe the analytic properties of scattering amplitudes in N=4 super Yang-Mills theory, with the focus on high order corrections to the six-particle MHV amplitude. By making an ansatz for the analytic structure and imposing physical constraints, including matching the BFKL expansion in multi-Regge kinematics and the operator product expansion for the dual Wilson loop in the near-collinear regime, we are able to explicitly construct the amplitude to four loops in perturbation theory.</em>
• String Theory Seminar
3 March 2014
12:00
Toby Wiseman
Abstract
<em>I will review the link between 1+p dimensional maximally supersymmetric Yang-Mills and the black hole thermodynamics of Dp-branes via the gauge/string correspondence. The finite temperature behaviour of Dp-brane supergravity black holes looks very alien from the perspective of the dual strongly coupled Yang-Mills. However, I will argue that in a natural set of Yang-Mills variables, the classical moduli (which unfortunately are still strongly coupled), certain features of these thermodynamics become quite transparent. A physical picture then emerges of the black holes as a strongly interacting 'soup' of these moduli.</em>
• String Theory Seminar
24 February 2014
12:00
Tristan McLoughlin
Abstract
<em> The study of the world-sheet S-matrix for AdS_5 x S^5 strings was a key step in the complete determination of the spectrum of anomalous dimensions for planar N=4 super-Yang-Mills. To go beyond the spectral problem it is important to consider higher-point worldsheet correlation functions and, as is standard in many integrable models, one approach is the study of form factors. We will discuss the all-order functional equations that these objects must obey, their perturbative computation and their connection to four-dimensional gauge theory three-point functions. </em>
• String Theory Seminar
10 February 2014
12:00
Alejandra Castro
Abstract
<em> In this talk I will review the interpretation of Wilson line operators in the context of higher spin gravity in 2+1 dim and holography. I will show how a Wilson line encapsulates the thermodynamics of black holes. Furthermore it provides an elegant description of massive particles. This opens a new window of observables which will allow us to probe the true geometrical nature of higher spin gravity.</em>
• String Theory Seminar
3 February 2014
12:00
Johannes Schmude
Abstract
<em> I this talk, I will discuss two entirely different classes of super Yang-Mills theories; the four dimensional SCFTs dual to AdS x Y where Y is Sasaki-Einstein, and five dimensional theories defined directly on such manifolds. What the two classes have in common is that they lend themselves to the application of Kohn-Rossi cohomology. Intuitively, one can think of this as an odd-dimensional relative of Dolbeault cohomology. Kohn-Rossi cohomology groups appear naturally when doing supergravity calculations of superconformal indices in the first class of theories or when calculating the partition functions of the latter using localisation. After a brief introduction to the relevant aspects of Sasaki-Einstein geometry, I will give an overview of both these applications. </em>
• String Theory Seminar