2014-2015
All seminars take place on Wednesdays at 1pm in room 54/7035, unless otherwise indicated.
Please scroll down the page to read the abstracts.
18/09/14 - Simon Gentle (UCLA) - Entanglement entropy of Wilson loops: Holography and matrix models
08/10/14 - Hansjoerg Zeller (Munich) - Hydrodynamic Regimes of Spinning Black D3 Branes
15/10/14 - Tim Adamo (DAMTP) - Gravity as a worldsheet theory
22/10/14 - Da-Wei Pang (Southampton) - Confinement and phase transition in holographic entanglement entropy
28/10/14 - Michael Ferlaino (Swansea) - A universal correction to higher spin entanglement entropy
(11am 54/8033)
29/10/14 - Inês Aniceto (Lisbon) - Resurgence of Localizable Observables in Supersymmetric Gauge Theories
05/11/14 - Elli Pomoni (DESY & NTU Athens) - Integrability and Exact Effective Couplings in N=2 gauge theories
12/11/14 - Vasco Gonçalves (Porto) - Regge theory for correlation functions in CFTs
18/11/14 - Alexander Krikun (NORDITA) - Striped phase in holographic d-wave superconductor (11am 54/8033)
19/11/14 - Benson Way (DAMTP) - Hovering Black Holes from Charged Defects
26/11/14 - Tomás Andrade (Oxford) - Simple models of holographic superconducting lattices
27/11/14 - Alex Arvanitakis (DAMTP) - Unitarity in Holographic, Massive 3D Gravity (3pm 46/2003 L/T B)
03/12/14 - Ioannis Papadimitriou (IFT Madrid) - Hyperscaling violating Lifshitz holography
10/12/14 - Carmen Li (Edinburgh) - Three-dimensional black holes and descendants
- Christmas break -
07/01/15 - Paul McFadden (Imperial) - Soft limits in holographic cosmology (arXiv:1412.1874)
14/01/15 - Adam Bzowski (KU Leuven) - Dimensional renormalization in AdS/CFT
28/01/15 - Tom Griffin (Imperial) - Lifshitz Field Theories: Naturalness, Polynomial Shift Symmetries and Graphs
04/02/15 - Ricardo Monteiro (Oxford) - Gravity as gauge theory squared: from amplitudes to black holes
11/02/15 - Adi Armoni (Swansea) - Non-Supersymmetric Seiberg Dualities from String Theory
18/02/15 - No seminar
25/02/15 - Carlisson Miller (IFT Sao Paulo) - Pseudoscalar meson excitations in AdS/QCD
04/03/15 - Joan Simon (Edinburgh) - Quantum entanglement of locally perturbed thermal states
11/03/15 - Philipp Kleinert (Oxford) - Non-Equilibrium Dynamics in AdS/CFT: The Holographic Dictionary and Quantum Quenches
18/03/15 - Jyotirmoy Bhattacharya (Durham) - A quasi-local measure of quantum entanglement
- Easter break -
22/04/15 - Nikolay Bobev (KU Leuven) - Holography for N=2* on S4
29/04/15 - Mario Flory (MPI Munich) - Entanglement entropy in a holographic model of the Kondo effect
06/05/15 - David Turton (CEA Saclay) - AdS/CFT for BPS and non-BPS black hole microstates
13/05/15 - Takaaki Ishii (Crete Center for Theoretical Physics, Heraklion) - Turbulent strings in AdS/CFT
20/05/15 - Andrew Hickling (Imperial) - Bulk Duals for Generic Static, Scale-Invariant Holographic CFT States
27/05/15 - Nabil Iqbal (Amsterdam) - Electric fields and quantum wormholes
30/06/15 - Claudio Coriano (Salento U and Southampton U) - Superconformal sum rules and the spectral density flow of the composite dilaton (ADD) multiplet in N=1 theories - (3pm 54/5B)
01/07/15 - Emil Mottola (Los Alamos) - What’s the (Quantum) Matter with Black Holes? Dark Energy and Condensate Stars
09/07/15 - Henry Maxfield (Durham) - Entanglement and gravity in three dimensions
Abstracts
Entanglement entropy of Wilson loops: Holography and matrix models
Simon Gentle (UCLA)
A half-BPS circular Wilson loop in maximally supersymmetric SU(N) Yang-Mills theory in an arbitrary representation is described by a Gaussian matrix model with a particular insertion. The additional entanglement entropy of a spherical region in the presence of such a loop was recently computed by Lewkowycz and Maldacena using exact matrix model results.
In this talk I will utilise the supergravity solutions that are dual to such Wilson loops in large representations to calculate this entropy holographically. Employing the results of Gomis, Matsuura, Okuda and Trancanelli to express this holographic entanglement entropy in a matrix model language, I will demonstrate complete agreement with the formula derived by Lewkowycz and Maldacena.
Hydrodynamic Regimes of Spinning Black D3 Branes
Hansjoerg Zeller (Munich)
In this talk we present the hydrodynamic regime of non-extremal spinning black D3 branes. We analyse the system on a cut off surface with Dirichlet boundary conditions for the space-time fluctuations. The long-wavelength description of the intrinsic world-volume dynamics of the surface is encoded in the induced stress energy tensor and in two induced distinct charge currents. We present the results for the shear viscosity, the diffusion constant and the chiral anomaly coefficient. In the near-horizon region these coefficients limit to the well-known results calculated in the context of fluid/gravity duality.
Gravity as a worldsheet theory
Tim Adamo (DAMTP)
Over the past ten years, increasingly simple expressions for the tree-level S-matrix of (super)gravity have been found. These amplitude expressions, which are totally unexpected from a space-time Lagrangian point-of-view, should be telling us something about GR as a non-linear field theory, namely, that it is simpler on-shell than the Einstein-Hilbert action makes it seem. Building from these advances in scattering amplitudes, I will show that GR (or more generally, type II SUGRA in 10d) can be formulated as a worldsheet CFT which is basically free. This story is analogous to, but also crucially different from, the way in which non-linear target space field equations emerge from string theory.
Confinement and phase transition in holographic entanglement entropy
Da-Wei Pang (Southampton)
Via a holographic approach, we explore the relation between confinement in a given gravity background and a phase transition occurring in the entanglement entropy. As example for the bulk gravity theory, we consider Einstein’s gravity coupled to a scalar field, including a nontrivial potential. This action may originate from a certain non-critical string theory. The asymptotic UV geometry is assumed to be AdS, while there is a curvature singularity in the deep IR. We calculate the entanglement entropy in these backgrounds, with the entangling region being either a strip or a sphere. We find the conditions for the occurrence of the phase transition in the entanglement entropy. These conditions do not coincide with the requirements for confinement. Therefore our results suggest that confinement and phase transition in the entanglement entropy are not inherently related.
A universal correction to higher spin entanglement entropy
Michael Ferlaino (Swansea)
Within the context of the duality between higher spin gravitational theories and a semi- classical limit of WN minimal models, we consider 2D CFTs with W∞ symmetry at finite temperature, deformed by the presence of a chemical potential for the spin–three current. As a perturbative expansion in the chemical potential, we compute the Renyi and entanglement entropies for a single interval. The leading correction is universal and matches the holographic result, based on Wilson line functionals, obtained from the higher spin gravitational dual.
Resurgence of Localizable Observables in Supersymmetric Gauge Theories
Inês Aniceto (Lisbon)
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. To capture the non-perturbative effects behind these divergences one can then use resurgence analysis. Resurgence has been successfully applied to the study of many quantum observables, from energy eigenvalues and ambiguity cancelations in quantum mechanics to the free energies of matrix models and topological strings. Presently, after a brief discussion of resurgence techniques, we will focus of observables of certain gauge theories which have a finite dimensional matrix model representation via localization techniques. We will discuss their asymptotic properties, and show how resurgence analysis can provide great insight into the non-pertubative features of those observables.
Integrability and Exact Effective Couplings in N=2 gauge theories
Elli Pomoni (DESY & NTU Athens)
Any N=2 gauge theory in four dimensions contains a set of local operators made only out of fields in the N=2 vector multiplet that is closed under renormalization to all loops, namely the SU(2,1|2) sector. We present a diagrammatic argument that for any planar N=2 theory the SU(2,1|2) Hamiltonian acting on infinite spin chains is identical to all loops to that of N=4 SYM, up to a redefinition of the coupling constant g^2 → f(g^2). Thus, this sector is integrable and anomalous dimensions can be read off from the N=4 ones up to this redefinition. For each N=2 theory the universal function f(g) can be obtained by computing the circular Wilson loop using localization and comparing it to the N = 4 one.
Regge theory for correlation functions in CFTs
Vasco Gonçalves (Porto)
In this talk we will try to motivate why the study of the Regge limit in a correlation function of a conformal field theory is interesting. We will review the results obtained in the past few years and present some on going work in phi^3 theory using skeleton expansion.
Striped phase in holographic d-wave superconductor
Alexander Krikun (NORDITA)
In its most general formulation the gauge/string duality may be used to build models of various strongly coupled systems in condensed matter. One of these is high-temperature d-wave superconductor. The holographic model of d-wave superconductor includes the dynamics of spin-2 charged field on top of the curved AdS geometry. In the probe approximation the model may be formulated consistently and exhibits a number of interesting physical phenomena. The important task is to classify all possible ground states of the model, which will correspond to the various phases of the dual system, and study the resulting phase diagram. In this talk I will discuss the recently found ground state which exhibits the stripes of charge density, violates the translation symmetry spontaneously and may be associated with the pseudogap state in high-Tc superconductors.
Hovering Black Holes from Charged Defects
Benson Way (DAMTP)
We construct the holographic dual of an electrically charged, localised defect in a conformal field theory at strong coupling. In so doing, we find that the theory can sometimes flow to new IR fixed points. For an impurity with sufficiently large amplitude, we find that a new gravitational phenomenon occurs: a spherical extremal Reissner-Nordstrom black hole nucleates in the bulk - a hovering black hole. This is a second order quantum phase transition. We construct this new phase with several profiles for the chemical potential and study its properties. We find an apparently universal curve for the entropy of the defect as a function of its amplitude. We comment on the possible field theory implications of our results.
Simple models of holographic superconducting lattices
Tomás Andrade (Oxford)
Abstract: we will discuss two mechanisms of momentum relaxation in holography which preserve homogeneity in the bulk geometry. Studying the condensation of a complex scalar field on these black hole solutions we will describe superconductivity on the dual theory. We will then compute the optical conductivity of the so constructed black holes and compare with other models in the literature.
Unitarity in Holographic, Massive 3D Gravity (3pm 46/2003 L/T B)
Alex Arvanitakis (DAMTP)
The recent model of three-dimensional massive gravity known as ``Minimal Massive Gravity'' (MMG) is the simplest known (hence ``minimal'') example of a gravitational theory that satisfies basic requirements of both bulk and boundary unitarity in the semi-classical approximation while propagating bulk degrees of freedom. In this talk we will outline how MMG evades the ``bulk/boundary unitarity clash'' on asymptotically AdS backgrounds and discuss features of the flat-space limit. Should time allow we will also illustrate MMG's improved short-distance behaviour by showing how the theory resolves the Big Bang singularity of 3D FLRW cosmologies into a ``Big Bounce''.
Hyperscaling violating Lifshitz holography
Ioannis Papadimitriou (IFT Madrid)
Holographic techniques have been instrumental in understanding certain aspects of strongly correlated systems, both in high energy and condensed matter physics. One of the most interesting applications of holography in the condensed matter setting is the study of quantum critical points exhibiting Lifshitz or hyperscaling violating Lifshitz symmetry. I will present a general method for systematically constructing the holographic dictionary for both Lifshitz and hyperscaling violating Lifshitz backgrounds with arbitrary dynamical exponents and for a large class of bottom up models admitting such backgrounds. This allows us to determine quite generically various physical properties of the dual non-relativistic systems, such as the spectrum of operators, the holographic Ward identities, the conformal anomalies, renormalized correlation functions, as well as their thermodynamic properties.
Three-dimensional black holes and descendants
Carmen Li (Edinburgh)
We determine the most general three-dimensional vacuum spacetime with a negative cosmological constant containing a non-singular Killing horizon. We show that the general solution with a spatially compact horizon possesses a second commuting Killing field and deduce that it must be related to the BTZ black hole (or its near-horizon geometry) by a diffeomorphism. We show there is a general class of asymptotically AdS3 extreme black holes with arbitrary charges with respect to one of the asymptotic-symmetry Virasoro algebras and vanishing charges with respect to the other. We interpret these as descendants of the extreme BTZ black hole.
Soft limits in holographic cosmology (arXiv:1412.1874)
Paul McFadden (Imperial)
The correlation functions of primordial perturbations provide vital clues to the physics of the early universe. The soft limits of these correlation functions, in which one or more momenta vanish, are especially simple and exhibit nearly model-independent behaviour described by the inflationary consistency relations. In this talk, we discuss these consistency relations from a holographic perspective, showing how they arise from diffeomorphism invariance in the three-dimensional dual quantum field theory description. In this fashion, we derive holographically the complete 3-point consistency relations for cosmological curvature perturbations and gravitons to subleading order, as well as new results for the soft limits of stress tensor correlators in quantum field theory.
Dimensional renormalization in AdS/CFT
Adam Bzowski (KU Leuven)
In the talk we will discuss possibilities of utilizing dimensional renormalization in holographic description of QFTs. Using a simple example of an interacting scalar field in the bulk we will show how the dimensional renormalization can be successfully applied in the context of AdS/CFT. In particular we will show a one-to-one correspondence between AdS and CFT counterterms leading to an unambiguous identification of the renormalization scale in AdS.
Lifshitz Field Theories: Naturalness, Polynomial Shift Symmetries and Graphs
Tom Griffin (Imperial)
Nonrelativistic QFTs of the Lifshitz type introduce many new and unusual phenomena. In particular, it becomes possible for Nambu-Goldstone modes associated with spontaneous symmetry breaking to exhibit higher-order dispersion relations. Such systems allow for an extension of the usual constant shift symmetry to a shift by a polynomial of degree P in spatial coordinates. These "polynomial shift symmetries" in turn protect the technical naturalness of modes with a higher-order dispersion relation, and lead to a refinement of the proposed classification of infrared Gaussian fixed points available to describe NG modes in nonrelativistic theories. Generic interactions in such theories break the polynomial shift symmetry explicitly to the constant shift. It is thus natural to ask: Given a Gaussian fixed point with polynomial shift symmetry of degree P, what are the lowest-dimension operators that preserve this symmetry, and deform the theory into a self-interacting scalar field theory with the shift symmetry of degree P? To answer this question, we have developed a new graph-theoretical technique, and used it to prove several classification theorems.
Gravity as gauge theory squared: from amplitudes to black holes
Ricardo Monteiro (Oxford)
We will discuss the relation between perturbative gauge theory and perturbative gravity, and look at how this relation extends to some exact classical solutions. First, we will review the double copy prescription that takes gauge theory amplitudes into gravity amplitudes, which has been crucial to progress in perturbative studies of supergravity. Then, we will see that the self-dual sectors provide an important insight into the relation between the theories. A key role is played by a kinematic algebraic structure mirroring the colour structure. Finally, we will see how these ideas extend to some exact classical solutions, namely black holes and plane waves. This leads to a relation of the type Schwarzschild as Coulomb charge squared.
Non-Supersymmetric Seiberg Dualities from String Theory
Adi Armoni (Swansea U)
In this talk I will consider brane configurations that include NS5 branes, orientifold planes and anti-branes. I will argue that the class of field theories that live on such brane configurations admit Seiberg duality. Interactions between branes and orientifold planes will be given a field theory interpretation. In particular a certain repulsive interaction will lead to a non-trivial Coleman-Weinberg potential and dynamical symmetry breaking.
Quantum entanglement of locally perturbed thermal states
Joan Simon (Edinburgh)
We will discuss how to compute the time evolution in quantum entanglement and correlations in thermal states that have been locally perturbed by a primary operator in 1+1 CFTs. in the large c limit. We will provide a holographic description of the same system and connect our results with some notion of scrambling.
Non-Equilibrium Dynamics in AdS/CFT: The Holographic Dictionary and Quantum Quenches
Philipp Kleinert (Oxford)
We review a formalism to compute correlation functions in quantum field theories suitable for systems far from equilibrium. Then, we address the same problem using the AdS/CFT correspondence. The two most attractive generalisations of the holographic dictionary to non-equilibrium situations are shown to be equivalent for two point functions of free bulk scalar fields. Finally, we study thermalization in a holographic model of a quantum quench as an example of a system far from equilibrium. Relevant Paper: 1412.2806 [hep-th]
A quasi-local measure of quantum entanglement
Jyotirmoy Bhattacharya (Durham)
In this talk, we shall introduce a quasi-local measure of quantum entanglement. It will be defined in terms of infinitesimal variations of the generating points, of the domain of dependence, associated with the subsystem, whose entanglement, we monitor. Restricting our attention to 1+1 and 2+1 dimensions, we will find that the condition of strong subadditivity requires this quantity to be positive semi-definite. Moving on to the holographic context, we will relate this inequality with the null energy condition in the bulk (at the linearised level).
Holography for N=2* on S4
Nikolay Bobev (KU Leuven)
I will discuss the gravitational dual of a mass deformation of N=4 SYM, called N=2* SYM, on S4. Using holographic techniques one can calculate the universal contribution to the corresponding free energy in the planar limit and at large 't Hooft coupling. The result matches the expression recently computed using supersymmetric localization in the field theory. This agreement provides a non-trivial precision test of holography in a non-conformal setting. I will also briefly discuss the extension of these results to mass deformations of N=4 SYM with N=1 supersymmetry.
Entanglement entropy in a holographic model of the Kondo effect
Mario Flory (MPI Munich)
My starting point is a holographic model of the Kondo effect recently proposed by Erdmenger et. al., i.e. of a magnetic impurity interacting with a strongly coupled system. Specifically, I focus on the challenges of computing gravitational backreaction in this model, which demands a study of the Israel junction conditions. I present general results on these junction conditions, including analytical solutions for certain toy models, that may be relevant also more generally in the AdS/boundary CFT correspondence. Furthermore, similar junction conditions for a bulk Chern-Simons field appearing in the holographic Kondo model are discussed. I then focus on the computation and interpretation of entanglement entropy in this holographic model.
AdS/CFT for BPS and non-BPS black hole microstates
David Turton (CEA Saclay)
The study of black hole microstates in string theory is an important problem, which has implications for the information paradox. Of particular interest are supergravity solutions describing BPS and near-BPS D1-D5-P bound states in string theory. These solutions have flat asymptotics, an AdS throat, and a 'cap' region at the bottom of the throat. I will present work which identifies the CFT description of a class of BPS D1-D5-P microstate geometries which describe degrees of freedom in the cap region. This class includes both regular solutions and solutions with conical defects. The CFT states may be described in terms of a generalized spectral flow operation which arises in the presence of twist operators. I will also describe work in progress on generalizing these results to a class of non-extremal black hole microstates, which radiate via a unitary version of Hawking radiation.
Turbulent strings in AdS/CFT
Takaaki Ishii (Crete Center for Theoretical Physics, Heraklion)
I will talk about nonlinear dynamics of the flux tube between an external quark-antiquark pair in N=4 SYM using the gravity dual given by a string in AdS. I will numerically compute the nonlinear time evolution of the string when the endpoints are perturbed in various ways. Results show cusp formation on the string. I will then discuss a connection between this phenomenon and turbulent behavior in the energy spectrum. This talk is based on arXiv:1504.02190.
Bulk Duals for Generic Static, Scale-Invariant Holographic CFT States
Andrew Hickling (Imperial)
Certain static, near horizon geometries are now understood to be bulk duals to CFTs with static scale-invariant sources under the AdS/CFT correspondence. However, static near-horizon geometries aren't just scale-invariant, they have extra `enhanced' symmetry. This means that they can only be the bulk duals for the special class of static, scale-invariant sources that share this enhanced symmetry. In this talk I will present numerical constructions of bulk duals for more generic static, scale-invariant sources, without this extra symmetry. These solutions are quite different to near-horizon geometries. In place of the extremal horizon they have a null singularity. I will discuss the potential relevance of these geometries to the problem of finding the IR geometry in the bulk dual for more generic CFT source terms.
Electric fields and quantum wormholes
Nabil Iqbal (Amsterdam)
A classical Einstein-Rosen bridge changes the topology of spacetime, allowing (for example) electric field lines to penetrate it. It has recently been suggested that in the bulk of a theory of quantum gravity, the quantum entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the quanta, or a “quantum wormhole”. For this “ER=EPR” correspondence to make sense it then seems necessary for a quantum wormhole to allow (for example) electric field lines to penetrate it. I will discuss (within low-energy effective field theory) in detail what it means for an electric field to penetrate a region of space and whether or not this happens for a quantum wormhole.
What’s the (Quantum) Matter with Black Holes? Dark Energy and Condensate Stars
Emil Mottola (Los Alamos National Laboratory)
General Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degree of freedom generated by the trace anomaly. At event horizons the conformal anomaly scalar degree of freedom can have macroscopically large effects on the geometry, potentially removing the classical event horizon of a black hole, replacing it with a quantum boundary layer where the effective value of the gravitational vacuum energy density can change. In the full effective theory, the cosmological term becomes a dynamical condensate, whose value depends upon boundary conditions near the horizon. By taking a positive value in the interior of a fully collapsed star, the effective cosmological term removes any singularity, replacing it with a smooth dark energy interior. The resulting gravitational condensate star (or gravastar) configuration resolves all black hole paradoxes, and provides a testable alternative to black holes as the final state of complete gravitational collapse. The observed dark energy of our universe likewise may be a macroscopic finite size effect whose value depends on the cosmological horizon scale.
Entanglement and gravity in three dimensions
Henry Maxfield (Durham)
Quantum entanglement has played a central role in recent advances in diverse fields of study. In particular, in the context of quantum gravity and holographic duality, there are hints that entanglement is intimately related to the emergence and connectedness of geometry.
Gravity in three dimensions is particularly simple, so it offers a rich and powerful laboratory for exploring these ideas. I’ll describe how entanglement entropies in states dual to solutions of pure 3D gravity can be computed extremely simply and purely algebraically, and then show that wormholes joining multiple exterior regions can be built from CFT states with a very simple local, bipartite entanglement structure.