Strong Fields, Strings and Holography

Talks

Venue: James Callaghan Lecture Theatre



Allan Adams:   Holography and Turbulence

Abstract: Holography provides a powerful tool with which to study far-from-equilibrium dynamics in both gravity and in field theory. In this talk I will describe two lessons about turbulent dynamics derived from a combination of numerical and analytic computations. First, I will demonstrate that turbulent flows in strongly-coupled 2d superfluids exhibit a direct cascade form IR to UV, in sharp contrast to turbulent flows in normal 2d fluids such as the upper atmosphere. Second, I will show that the horizon dual to a turbulent steady-state must be a fractal with fractal dimension d+4/3. Along the way, we will see that many dynamical problems in AdS numerical relativity can be effectively solved by numerically solving the Hydrodynamic equations in one lower dimension.



Jan de Boer: Entanglement Entropy in Higher Spin Theories

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Nick Dorey: Integrability and DLCQ



Johanna Erdmenger: New aspects of Universality in Gauge/Gravity Duality

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Sebastian Franco: A New Class of QFTs: from D-branes to On-Shell Diagrams

Abstract: Over the last decade, we have witnessed remarkable progress in our understanding of Quantum Field Theories. New insights have emerged from a multitude of fronts, ranging from the Gauge/Gravity Correspondence to Integrability. In this seminar I will discuss Bipartite Field Theories (BFTs), a new class of QFTs embodying many of these new approaches. BFTs are 4d, N=1 quiver gauge theories with Lagrangians defined by bipartite graphs on Riemann surfaces. Remarkably, they underlie a wide spectrum of interesting physical systems, including: D-branes probing Calabi-Yau manifolds, their mirror configurations, integrable systems in (0+1) dimensions and on-shell diagrams in N=4 SYM. I will introduce new techniques for studying these gauge theories. I will explain how their dynamics is captured graphically and the interesting emergence of concepts such as Calabi-Yau manifolds, the Grassmannian and cluster algebras in the classification of IR fixed points. Finally, I will introduce a new framework for analyzing general systems of D3 and D7-branes over toric Calabi-Yau 3-folds. These ideas can be exploited for embedding BFTs in String Theory but have a much wider range of applicability.



Stanislav Kuperstein : Spacetime Emergence via Holographic RG Flow from Incompressible Navier-Stokes at the Horizon

Abstract:We show that holographic RG flow can be defined precisely such that it corresponds to emergence of spacetime. We consider the case of pure Einstein's gravity with a negative cosmological constant in the dual hydrodynamic regime. The holographic RG flow is a system of first order differential equations for radial evolution of the energy-momentum tensor and the variables which parametrize it's phenomenological form on hypersurfaces in a foliation. The RG flow can be constructed without explicit knowledge of the bulk metric provided the hypersurface foliation is of a special kind. The bulk metric can be reconstructed once the RG flow equations are solved. We show that the full spacetime can be determined from the RG flow by requiring that the horizon fluid is a fixed point in a certain scaling limit leading to the non-relativistic incompressible Navier-Stokes dynamics. This restricts the near-horizon forms of all transport coefficients, which are thus determined independently of their asymptotic values and the RG flow can be solved uniquely. We are therefore able to recover the known boundary values of almost all transport coefficients at the first and second orders in the derivative expansion. We conjecture that the complete characterisation of the general holographic RG flow, including the choice of counterterms, might be determined from the hydrodynamic regime.



Neil Lambert:   Making Up for Lost Time: Emergent Time and the M5-brane

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Marcos Marino:   Non-perturbative Effects in Large N Theories and Strings

Abstract: String/gauge dualities can be used in principle to learn about non-perturbative effects in string theory and M-theory: string and membrane instantons should be given by exponentially small corrections to the 1/N expansion. In this talk I will provide a complete answer for these corrections in the case of the partition function of ABJM theory on the three-sphere: string instantons are encoded in a topological string, while membrane instantons are encoded in the Nekrasov-Shatashvili limit of a refined topological string. The answer shows, in a precise quantitative way, that perturbative string theory is radically insufficient at strong coupling, and needs to be supplemented by a theory of membranes. This result also suggests a new perspective on non-perturbative topological strings on local Calabi--Yau manifolds. In this new point of view, the starting point is the Nekrasov-Shatashvili limit, and the usual perturbative expansion of the unrefined topological string appears as an instanton effect.



Dario Martelli:   Supersymmetric Gauge Theories on Curved Manifolds and their Gravity Duals

Abstract: I will discuss recent results concerning supersymmetric field theories on curved manifolds preserving (rigid) supersymmetry, both in three and for four dimensions. Moreover, I will present gravity dual solutions to such gauge theories, providing new non-trivial tests of the gauge/gravity duality.



Sameer Murthy:   Quantum Black Hole Entropy and the Holomorphic Prepotential

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Andy O' Bannon:   A Holographic Model of the Kondo Effect

Abstract: The Kondo effect occurs in metals doped with magnetic impurities in the ground state an electron binds to 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, which may provide a new approach to the multiple-impurity Kondo problem.



Michela Petrini:   10 Dimensional Structures and Holography

Abstract: We will review how the formalism of generalised geometry provides useful tools to study backgrounds relevant for the gauge/gravity duality also for non relativistic backgrounds and black-hole microstates



Jorge Russo:   Massive N = 2 Gauge Theories at Large N

Abstract:Using exact results obtained from localization, we explore the large N limit of N = 2 super Yang-Mills gauge theories with massive matter multiplets. In the case of N = 2* theory, we find a novel type of phase transitions,  associated with the appearance of new nearly massless particles in the spectrum. As the coupling is increased, the theory undergoes an infi nite sequence of phase transitions that accumulate at infinite coupling. The strong coupling limit agrees with AdS/CFT and arises by a coarse-grain average over a rather irregular fractal structure at small scales. On the other hand, a massive theory with fundamental matter exhibits a smooth interpolation between the weak and strong coupling regime.



Kostas Skenderis:   AdS/Ricci-flat Correspondence

Abstract: In this talk I will first introduce generalized dimensional reduction as a method for obtaining the holographic dictionary for spacetimes with non-AdS asymptotics from that of AdS. Then I will use generalized dimensional reduction in order to obtain a correspondence between a class of asymptotically AdS spacetimes and a class of Ricci-flat spacetimes. Finally, I will discuss a number of examples and applications.



Daniel Thompson:   Aspects of Non-Abelian T-Duality

Abstract: I will review recent progress in the use of non-abelian T-duality in supergravity. I will provide an overview of some new N=1 solutions of (massive) IIA theory and discuss them in the context of the AdS/CFT correspondance. I will present new results concerning the underlying geometrical structures of these solutions and their relation to generalised geometry. Time permitting I shall also present novel supersymmetric solution of M-theory obtained by dualisation of Y^{p,q} spaces. This talk will be based on: 1305.7229; 1301.6755; 1212.4840; 1012.1320 together with some ongoing work.



Gabriele Travaglini :   The Return of the Analytic S-matrix

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David Tong:   Gauge Dynamics and Topological Insulators

Abstract: I'll describe how some simple aspects of topological insulators sit within the familiar context of non-abelian gauge theories. More specifically, I'll show how to compute TKNN invariants for SU(2) Yang-Mills.



Brian Wecht:   Exploring the 4d Superconformal Zoo

Abstract: Over the past several years, it has become increasingly apparent that many interesting and tractable superconformal field theories (SCFTs) can be realized without resorting to a UV Lagrangian description. Although many of these theories have N=2 supersymmetry, these is an even larger class of N=1 theories that can be studied, certain aspects of which remain calculable despite the reduced amount of supersymmetry. In this talk, I will give an introduction to these N=1 theories, how they can be realized via M-theory and F-theory, and which tools we can use to explore them.