Past 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
27 January 2014
12:00
José Morales
Abstract
<em> We study N=2 flux vacua describing intrinsic non-perturbative systems of 3- and 7-branes. In the spirit of F-theory, the solutions are described in purely geometric terms with the flux data codified on CY geometries given as K3 fibrations over a two-sphere. </em>
  • String Theory Seminar
20 January 2014
12:00
Andy O'Bannon
Abstract
<em> The Kondo effect occurs in metals doped with magnetic impurities: in the ground state the electrons form a screening cloud around each impurity, leading to dramatic changes in the thermodynamic and transport properties of the metal. Although the single-impurity Kondo effect is considered a solved problem, many questions remain, especially about the fate of the Kondo effect in the presence of multiple impurities. In particular, for a sufficiently dense concentration of impurities, a competition between the Kondo effect and inter-impurity interactions can lead to quantum criticality and non-Fermi liquid behavior, which remains poorly understood. In this talk I will present a model of the single-impurity Kondo effect based on holography, also known as gauge-gravity duality or the AdS/CFT correspondence, which may serve as a foundation for a new approach to the multiple-impurity system.</em>
  • String Theory Seminar
25 November 2013
12:00
Ruxandra Moraru
Abstract
In this talk, we discuss an analogue of the Hermitian-Einstein equations for generalized Kaehler manifolds proposed by N. Hitchin. We explain in particular how these equations are equivalent to a notion of stability, and that there is a Kobayahsi-Hitchin-type of correspondence between solutions of these equations and stable objects. The correspondence holds even for non-Kaehler manifolds, as long as they are endowed with Gauduchon metrics (which is always the case for generalized Kaehler structures on 4-manifolds). This is joint work with Shengda Hu and Reza Seyyedali.
  • String Theory Seminar
18 November 2013
12:00
Nadav Drukker
Abstract
<em>N=4 supersymmetric Yang-Mills is probably the simplest interacting quantum field theory in four dimensions. Likewise its gravity dual:AdS_5 x S^5 is one of the simplest string theory backgrounds. This string background is much harder to study than flat space since the spectrum is not given by free oscillators, yet it is integrable, meaning that there is an infinite number of conserved charges on the world-sheet. Over the past 10 or so years the tools of integrability have been developed and applied to study this theory. In my talk I will present two recent applications of these tools to the study of the spectrum of open strings. The first problem is the potential between charged particles - the N=4 analogues of a quark and an antiquark. The second is the ground state of an open string stretched between a D-brane and an anti D-brane which is the tachyon of perturbative (non SUSY) string theory. My talk will be geared to a general theoretical physics audience and will not dwell too much on the technicalities of the integrable model, which are rather involved and will try to focus mainly on the observables we study and the results we learnt about them.</em>
  • String Theory Seminar
11 November 2013
12:00
Susama Agarwalla
Abstract
<em>Symbols of multiple polylogs have recently become important in calculations of amplitudes in N=4 SYM. In this talk, I give a simple pictoral presentation of multiple polylogs and their symbols. I also discuss the Hopf algebraic structure underlying the multiple polylogs, and give some new relationships between different multiple polylogs based on the symmetries of my pictoral presentation that are exact on the symbol level, but complicated on the level of the actual multiple polylogs..</em>
  • String Theory Seminar
4 November 2013
12:00
Jan Gutowski
Abstract
<em>Recent progress has been made in the analysis of supergravity solutions. It can be shown that for a large class of solutions, the conditions imposed by supersymmetry are equivalent to determining the zero modes of various types of Dirac operators, by an extension of the classical Lichnerowicz theorem. Hence the number of supersymmetries are constrained by index theory. For near-horizon black hole geometries, this mechanism produces symmetry enhancement.</em>
  • String Theory Seminar

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