Forthcoming events in this series


Mon, 03 Mar 2014

12:00 - 13:00
L5

On black hole thermodynamics from super Yang-Mills

Toby Wiseman
(Imperial College)
Abstract
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.
Mon, 24 Feb 2014

12:00 - 13:00
L5

World-Sheet Form Factors in AdS/CFT

Tristan McLoughlin
(Trinity College Dublin)
Abstract
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.
Mon, 10 Feb 2014

12:00 - 13:00
L5

Non-perturbative aspects of higher spin holography

Alejandra Castro
(Amsterdam)
Abstract
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.
Mon, 03 Feb 2014

12:00 - 13:00
L5

Partition functions and superconformal indices as applications of Kohn-Rossi cohomology

Johannes Schmude
(RIKEN)
Abstract
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.
Mon, 27 Jan 2014

12:00 - 13:00
L5

G-theory: U-folds as K3 fibrations

José Morales
(Roma 2 and Oxford)
Abstract
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.
Mon, 20 Jan 2014

12:00 - 13:00
L5

A Holographic Model of the Kondo Effect

Andy O'Bannon
(Oxford)
Abstract
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.
Mon, 25 Nov 2013

12:00 - 13:00
L5

A Kobayashi-Hitchin correspondence for generalized Kaehler manifolds

Ruxandra Moraru
(Waterloo)
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.

Mon, 18 Nov 2013

12:00 - 13:00
L5

Applications of integrability in AdS/CFT: On the quark-antiquark potential and the spectrum of tachyons

Nadav Drukker
(Kings College, London)
Abstract
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.
Mon, 11 Nov 2013

12:00 - 13:00
L5

Multiple Polylogs, symbols and polygons

Susama Agarwalla
(Oxford)
Abstract
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..
Mon, 04 Nov 2013

12:00 - 13:00
L5

Global Properties of Supergravity Solutions

Jan Gutowski
(Surrey)
Abstract
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.
Mon, 28 Oct 2013

12:00 - 13:00
L5

An Abundance of K3 Fibrations from Polyhedra with Interchangeable Parts

Philip Candelas
(Oxford)
Abstract
Even a cursory inspection of the Hodge plot associated with Calabi-Yau threefolds that are hypersurfaces in toric varieties reveals striking structures. These patterns correspond to webs of elliptic-K3 fibrations whose mirror images are also elliptic-K3 fibrations. Such manifolds arise from reflexive polytopes that can be cut intotwo parts along slices corresponding to the K3 fibers. Any two half-polytopes over a given slice can be combined into a reflexive polytope. This fact, together with a remarkable relation on the additivity of Hodge numbers, explains much of the structure of the observed patterns.
Mon, 21 Oct 2013

12:00 - 13:00
L5

Integrability and instability in AdS/CFT

Ryo Suzuki
(Oxford)
Abstract
The energy of an open string ending on giant-graviton branes in the AdS_5xS^5 spacetime is equal to the dimension of determinant-like operators in N=4 super Yang-Mills, according to AdS/CFT. We investigate this correspondence under a brane-antibrane setup by using gauge theory and integrability methods, and propose Boundary TBA equations to compute the exact dimensions of the determinant-like operators at any coupling. By solving the Boundary TBA numerically, we found a divergence of the exact energies at a finite value of the 't Hooft coupling constant, implying that string states are tachyonic at strong coupling. In this talk I would like to explain the origin of singularity after briefly reviewing the application of integrability methods to AdS/CFT.
Mon, 14 Oct 2013

12:00 - 13:00
L5

Higher-Spin Correlators

Agnese Bissi
(Oxford)
Abstract
In this talk I will discuss the three-point correlator of two protected scalar operators and one higher spin twist-two operator in N = 4 SYM, in the limit of large spin. This structure constant can be extracted from the OPE of the four-point correlator of protected scalar operators. Based on the OPE structure, symmetry arguments and intuition from the available perturbative results, it is possible to predict the structure constant at all loops in perturbation theory. This being so, it is natural to propose an expression for the all-loop four-point correlator in a particular limit.
Mon, 03 Jun 2013

12:00 - 13:00
L3

Emergent Time and the M5-Brane

Chris Hull
(Imperial College)
Abstract
One of the more dramatic effects that can arise in a theory at strong coupling is the opening up of an extra spatial dimension, as in IIA string theory or 5-dimensional maximally supersymmetric Yang-Mills theory. The aim of this talk is to investigate the possibility of an extra time dimension opening up in a similar way. The main focus will be on supersymmetric Yang-Mills theory in 5 Euclidean dimensions with 16 supersymmetries, which will be argued to have a strong coupling limit that is a theory in 5+1 dimensions, with a new time dimension opening up to give the (2,0) theory. This gives new insight into the elusive (2,0) theory, which also arises as the M5-brane world-volume theory. It is interesting to have a theory formulated with no time dimension but from which time emerges, and may be useful in thinking about cosmological models in which time and/or space are emergent. The discussion raises questions about the role of time in quantum theory, and about the meaning of a compact time dimension.
Mon, 20 May 2013

12:00 - 13:00
L3

The Riemann Zeta Function and the Berry-Keating Hamiltonian

Philip Candelas
(Oxford)
Abstract
It is an old idea that the imaginary part of the nontrivial Riemann zeros s =-1/2 + iE might be related to the eigenvalues of a hermitean operator H, and so to a quantum mechanical system. Such a system has been proposed by Berry and Keating; it is a harmonic oscillator with the "wrong" signatureH=1/2(xp + px). The difficulty and interest in implementing this proposal is the need to find suitable boundary conditions, or a self adjoint extension for H, since the classical phase space orbits are hyperbolae rather than circles. I will review interesting observations of Mark Srednicki relating the ground state wave functions of the Berry Keating hamiltonian and the conventional harmonic oscillator hamiltonian to the zeta function.
Mon, 13 May 2013

12:00 - 13:00
L3

Stationary holographic plasma quenches and numerical methods for non-Killing horizons

Pau Figueras
(DAMTP)
Abstract
In this talk I will explain a new method to numerically construct stationary black holes with non-Killing horizons. As an example, I will use AdS/CFT to describe a time-independent CFT plasma flowing through a static spacetime which asymptotes to Minkowski in the flow's past and future, with a varying spatial geometry in-between. When the boundary geometry varies slowly, the holographic stress tensor is well-described by viscous hydrodynamics. For fast variations it is not, and the solutions are stationary analogs of dynamical quenches, with the plasma being suddenly driven out of equilibrium. We find evidence that these flows become unstable for sufficiently strong quenches and speculate that the instability may be turbulent. The gravitational dual of these flows are the first examples of stationary black holes with non-Killing horizons.
Mon, 06 May 2013

12:00 - 13:00
L3

Torsion-free generalized connections and heterotic supergravity

Mario Garcia Fernandez
(EPFL)
Abstract
I will present a new derivation of the equations of motion of Heterotic supergravity using generalized geometry, inspired by the geometric description of 11-dimensional and type II supergravity by Coimbra, Strickland-Constable and Waldram. From a mathematical point of view, this arises from the study of torsion-free generalized connections on a non-exact Courant algebroid. We will find that the freedom provided by the dilaton field in the physical theory can be interpreted as the freedom of choice of Levi-Civita connection in generalized geometry.
Mon, 29 Apr 2013

12:00 - 13:00
L3

Hyperconifold Singularities and Transitions

Rhys Davies
(Oxford)
Abstract
I will discuss a class of isolated singularities, given by finite cyclic quotients of a threefold node (conifold), which arise naturally in compact Calabi-Yau threefolds. These singularities admit projective crepant resolutions, and thereby give rise to topological transitions between compact Calabi-Yau spaces. Among the interesting properties of such 'hyperconifold transitions' is that they can change the fundamental group, and are related by mirror symmetry to familiar conifold transitions. Having established these mathematical properties, I will briefly discuss some applications, as well as the physics of type IIB string theory compactified on a space with a hyperconifold singularity.
Mon, 25 Feb 2013

12:00 - 13:00
L3

Fenchel-Nielsen coordinates from spectral networks

Lotte Hollands
(Oxford)
Abstract
Fenchel-Nielsen coordinates play a central role in constructing partition functions for theories of class S with gauge group SU(2). Having an analogue of these coordinates for higher rank gauge groups is a first step in finding partition functions for strongly coupled gauge theories of the Minahan-Nemeschansky type. We find such a generalization through the formalism of spectral networks and the non-abelianization map, that was originally introduced by Gaiotto, Moore and Neitzke to find a better understanding of BPS states in the theories of class S. This is joint work with Andy Neitzke.
Mon, 18 Feb 2013

12:00 - 13:00
L3

A magic square from Yang-Mills squared

Mike Duff
(Imperial College)
Abstract
I will give a division algebra R,C,H,O description of D = 3 Yang-Mills with N = 1,2,4,8 and hence, by tensoring left and right multiplets, a magic square RR, CR, CC, HR, HC, HH, OR, OC, OH, OO description of D = 3 supergravity with N = 2, 3, 4, 5, 6, 8, 9, 10, 12, 16.
Mon, 11 Feb 2013

12:00 - 13:00
L3

On sequestering and decoupling in stabilized string models

David Marsh
(Oxford)
Abstract
I will describe recent efforts to understand the mediation of supersymmetry breaking in stabilized compactifications of type IIB string theory. By geometrically separating the visible sector from the supersymmetry breaking effects one may hope to achieve sequestered supersymmetry breaking and much ameliorated constraints from bounds on flavor changing neutral currents. However, in this talk I will discuss how non-perturbative superpotential cross-couplings between the visible sector and the Kähler moduli may spoil sequestering and introduce a sensitivity to the global details of the compactification. As a simple example, I will describe the structure of these `de-sequestering’ operators for a class of visible sectors realized by D-branes probing an orbifold singularity, and I will discuss their importance in the KKLT and LVS moduli stabilization scenarios.