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Workshop Programme

for period 16 - 20 September 2013

Holography: from gravity to quantum matter

16 - 20 September 2013

Timetable

Monday 16 September
08:30-08:50 Registration
08:50-09:00 Welcome by Christie Marr, Deputy Director of the Institute
09:00-09:45 Horowitz, G (University of California, Santa Barbara)
  A simple holographic model of nonlinear conductivity Sem 1
 

I will present a simple gravitational solution which describes the holographic dual of a conductor, which goes beyond the usual linear response. In particular it includes Joule heating.

 
09:45-10:30 Sachdev, S (Harvard University)
  Conformal field theories in a periodic chemical potential Sem 1
 

Co-authors: Andrew Lucas (Harvard University), Paul Chesler (Harvard University)

We compare field-theoretic and holographic results on the structure of 2+1 dimensional conformal field theories placed in a periodic chemical potential with amplitude V and wavevector k. General arguments are presented that the infrared limit is described by an emergent conformal field theory whose universality class changes at an infinite discrete set of values of V/k. Electrical transport properties are computed: the holographic method captures some, but not all, of the expected structure.

 
10:30-11:00 Morning Coffee
11:00-11:45 Weng, ZY (Tsinghua University)
  Mott physics, sign structure, and high-TC superconductivity Sem 1
 

Fermion sign structure constitutes the foundation of the Landau’s Fermi liquid theory in condensed matter physics. But it will be fundamentally changed by the strong interaction in the so-called doped Mott insulator relevant to high-Tc cuprate materials. New novel sign structure as reduced Fermion signs will appear here, which can be precisely captured by a nonintegrable phase factor like emergent topological gauge fields in the simplest doped Mott insulators: the t-J and Hubbard models. The quantum interference of the altered Fermion signs will result in non-Fermi-liquid/non-BCS-type normal/superconducting phenomena, which may provide a systematical understanding of the anomalous properties observed in cuprate superconductors.

 
11:45-12:30 Phillips, PW (University of Illinois at Urbana-Champaign)
  Unparticles and strongly correlated electron matter Sem 1
 

Co-authors: Bandon Langley (University of Illinois), Jimmy Hutasoit (Pennsylvania State University)

One of the open problems in strong correlation physics is whether or not Luttinger's theorem works for doped Mott insulators. I will begin this talk by using this theorem to count particles and show that it fails in general for the Mott state. The failure stems from the divergent self energy that underlies Mottness. When such a divergence is present, charged degrees of freedom are present that have no particle interpretation. I will argue that such excitations are governed by a non-trivial IR fixed point and the propagator of which is of the unparticle form proposed by Georgi. I will show how a gravity dual can be used to determine the scaling dimension of the unparticle propagator. I will close by elucidating a possible superconducting instability of unparticles and demonstrate that unparticle stuff is likely to display fractional statistics in the dimensionalities of interest for strongly correlated electron matter.

 
12:30-13:30 Lunch at Wolfson Court
14:00-14:45 Hartnoll, S (Stanford University)
  Clumping and quantum order: Quantum gravitational dynamics of NUT charge Sem 1
 

I will derive the conditions under which NUT charge can proliferate in the gravitational path integral. Typically it will not proliferate. In these circumstances semiclassical GR is self-consistently quantum ordered in that the massless of the graviton is dynamically protected.

 
14:45-15:15 Betouras, J (Loughborough University)
  Lifshitz topological transition in interacting Fermi systems Sem 1
 

Co-authors: Sam T. Carr (Karsruhe Institute of Technology), Jorge Quintanilla (University of Kent), Sergey Slizovskiy (Loughborough University), Ziyang Meng (Louisiana State University), Kuanshing Chen (Louisiana State University), Mark Jarrell (Louisiana State University), Juana Moreno (Louisiana State University)

Recently, the theory of topological Lifshitz transition has become the focus of much attention in complex materials such as high-Tc superconductors, heavy fermions compounds etc. In this talk, we present three cases of topological Lifshitz transitions involving: (i) A Fermi liquid in two and three dimensions, interacting with short range interactions and exhibiting first order Lifshitz transition due to these interactions. The transition becomes more pronounced in the regime of paramagnons. The motivation for this work is provided by recent experiments on the material NaxCoO2.

(ii) The Hubbard model with negative next nearest neighbor hoping that shows to exhibit Lifshitz transition and a "multimode" quantum criticality associated with it and

(iii) Dipolar fermions in optical lattices where we consider an experimentally realizable two dimensional model of non-interacting chains of spinless fermions weakly coupled via a small inter-chain hopping and a repulsive inter-chain interaction. The phase diagram of this model has a surprising feature: an abrupt change in the Fermi surface as the interaction is increased.

The work at Loughborough has been supported by the Engineering and Physical Science Council.

 
15:15-15:45 Afternoon Tea
15:45-16:15 Pujolas, O (Universitat Autònoma de Barcelona)
  Emergent Lorentz invariance from strong dynamics Sem 1
 

Co-author: Sergey Sibiryakov (INR MNRAS Moscow)

I will discuss the phenomenon of emergent Lorentz invariance in strongly coupled theories, using the gauge/gravity correspondence to handle strong dynamics. The renormalization group flow towards Lorentz invariance is imprinted in the two-point functions of local operators and in the dispersion relations of the bound states. The deviations of these observables from the relativistic form at low energies are power-law suppressed by the ratio of the infrared and ultraviolet scales. I will comment on the implications for particle physics and condensed matter.

 
16:15-17:00 Aeppli, G (University College London)
  Quantum states in solids and their sensitivity to spectators and boundary conditions Sem 1
 

Examples of boson and fermion systems where interactions with spectators qualitatively change quantum phase transitions and states (e.g. from Fermi liquid to unconventional metal) are given. We also discuss how thermal boundary conditions can alter the states of macroscopic samples.

 
17:00-17:30 Green, A (University College London)
  Out of equilibrium quantum criticality and holography Sem 1
 

Co-authors: Andrew Berridge (University College London), Joel Moore (UC Berkeley), Shivaji Sondhi (Princeton), Julian Sonner (MIT), Ashwin Vishwanath (UC Berkeley)

The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady-state, leading to universal out-of-equilibrium behaviour. This attractive notion has been demonstrated in a number of cases upon which holography can provide a revealing perspective and new results. I will discuss the application of these ideas to a canonical 2-dimensional system driven out of equilibrium by the application of a strong in-plane electric field. I will focus upon the conditions required for the formation of a universal out of equilibrium steady state and its description using field theoretical and holographic methods. Non-trivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system.

 
17:30-18:30 Wine Reception
Tuesday 17 September
09:00-09:45 Pretorius, F (Princeton University)
  Numerical evolution of 5D asymptotically AdS spacetimes Sem 1
 

Co-authors: Hans Bantilan (University of Colorado), Stephen Gubser (Princeton University)

I will describe an approach to numerically solve Einstein gravity in 5-dimensional asymptotically Anti de Sitter spacetimes (AdS). The motivation is the gauge/gravity duality of string theory, with application to scenarios that on the gravity side are described by dynamical, strong-field solutions. For example, it has been argued that certain properties of the quark-gluon plasma formed in heavy-ion collisions can be modeled by a conformal field theory, with the dual description on the gravity side provided by the collision of black holes. As a first step towards modeling such more general phenomena, we initially focus on spacetimes with SO(3) symmetry in the bulk; i.e., axisymmetric gravity, dual to states with spherical or special conformal symmetry on the boundary. For a first application we study quasi-normal ringdown of highly deformed black holes in the bulk. Even though the initial states are far from equilibrium, the boundary state is remarkably well described as a hyd rodynamic flow from early times. The code is based on the generalized harmonic formulation of the field equations, and though this method has been shown to work well in many asymptotically flat scenarios, there are unique challenges that arise in obtaining regular, stable solutions in asymptotically AdS spacetimes. I will describe these challenges, and the way we have addressed them.

 
09:45-10:30 Holzegel, G (Imperial College)
  Stability and instability of asymptotically AdS black holes Sem 1
 

Co-authors: Jacques Smulevici (Université Paris-Sud (Orsay)), Claude Warnick (University of Warwick)

I will review some recent work regarding the dynamics of asymptotically anti de Sitter black holes. Emphasis will be put on two problems: The behaviour of linear waves on Kerr-AdS backgrounds, for which a logarithmic decay rate is established, and on the dynamics of the non-linear spherically-symmetric coupled Einstein-Klein-Gordon system. This is joint work with J. Smulevici. Finally, I will comment on extending these results to other boundary conditions for the scalar field, and investigate the relationship of boundary conditions and stability. This part is joint work with C. Warnick.

 
10:30-11:00 Morning Coffee
11:00-11:45 Bizon, P (Uniwersytet Jagiellonski)
  Globally regular instability of 3-dimensional anti-de Sitter spacetime Sem 1
 

Co-author: Joanna Jalmuzna (Jagiellonian University (Krakow))

We consider three-dimensional AdS gravity minimally coupled to a massless scalar field and study numerically the evolution of small smooth circularly symmetric perturbations of the AdS_3 spacetime. As in higher dimensions, for a large class of perturbations we observe a turbulent cascade of energy to high frequencies which entails instability of AdS_3. However, in contrast to higher dimensions, the cascade cannot be terminated by black hole formation because small perturbations have energy below the black hole threshold. We give evidence that the turbulence is too weak to produce a naked singularity and the evolution is globally regular in time, in accordance with the cosmic censorship hypothesis.

 
11:45-12:30 Lehner, L (Perimeter Institute for Theoretical Physics)
  The "turbulent'' side of gravity, stability and BH behavior Sem 1
 

Non-linear studies of AdS (either directly or indirectly through the fluid/gravity correspondence) indicate a rather complex phenomenology can arise. In particular, phenomena related to turbulence plays a key role in governing the behavior of perturbed black holes as well as stability of pure AdS. This talk will discuss these results and consequences of the observed behavior.

 
12:30-13:30 Lunch at Wolfson Court
14:00-14:30 Rostworowski, A (Uniwersytet Jagiellonski)
  Time-Periodic Solutions in an Einstein AdS Massless Scalar Field System Sem 1
 

Co-author: Maciej Maliborski (Jagiellonian University)

I will argue for the existence of stable, asymptotically anti- de Sitter (AdS), time-periodic solutions of Einstein equations. In particular, I will discuss the time-periodic solutions, recently discovered in Einstein AdS -- massless scalar field system, in d+1 spacetime dimensions at spherical symmetry (a joint work with Maciej Maliborski, Phys.Rev.Lett.111 051102). I will give two independent methods of construction of time-periodic solutions in this model, and argue that these solutions are stable (opposite to AdS solution itself).

 
14:30-15:00 Tanahashi, N (University of Tokyo)
  Horizon instability of an extreme Reissner-Nordstrom black hole Sem 1
 

Co-authors: James Lucietti (Edinburgh U), Keiju Murata (Keio U), Harvey S. Reall (Cambridge U)

Recently, a novel instability was found for a massless scalar field on an extreme Reissner-Nordstrom black hole. This instability is due to purely classical effect, and it makes a part of energy-momentum tensor of the scalar field discontinuous on the horizon at late time. We show that a similar instability occurs in also for a massive scalar field and for coupled linearized gravitational and electromagnetic perturbations. We also study numerically the nonlinear evolution of this instability for spherically symmetric perturbations of an extreme Reissner-Nordstrom (RN) black hole. We find that generically the endpoint of the instability is a non-extreme RN solution, while there exist fine-tuned initial perturbations for which the instability never decays. We discuss the physical mechanism and implications of this instability, and also argue the final fate of the system after nonlinear effects set in.

 
15:00-15:30 van der Schee, W (Universiteit Utrecht)
  From full stopping to transparency in a holographic model of heavy ion collisions Sem 1
 

Co-authors: Jorge Casalderrey-Solana (Universitat de Barcelona), Michal Heller (University of Amsterdam), David Mateos (Universitat de Barcelona), Paul Romatschke (University of Colorado), Scott Pratt (University of Michigan)

Numerically simulating colliding planar gravitational shock waves in AdS gives rise to rich and interesting dynamics. Wide shocks come to a full stop and expand hydrodynamically, as was found in [1]. High energy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms in the middle, quite akin to heavy-ion collisions. After an initial stage of far-from-equilibrium evolution the energy density and pressures become positive and are governed by hydrodynamics within a proper time 1/T, with T the local temperature at that time.

In the end I will comment on recent results where we were able to perform a somewhat similar simulation for central collisions and matched this with recent hydrodynamic and hadronic cascade codes, which enables an interesting comparison with transverse spectra for light particles.

[1] P.M. Chesler, L.G. Yaffe, (PRL 2011) [2] J. Casalderrey-Solana, M.P. Heller, D. Mateos, W. van der Schee, 1305.4919 [3] W. van der Schee, P. Romatschke, S. Pratt (to appear)

 
15:30-16:00 Afternoon Tea
16:00-16:30 Zhang, HQ (Chinese Academy of Sciences)
  A thermal quench induces spatial inhomogeneities in a holographic superconductor Sem 1
 

Co-authors: Antonio M. Garcia-Garcia (Cambridge), Hua Bi Zeng.

Holographic duality is a powerful tool to investigate the far-from equilibrium dynamics of superfluids and other phases of quantum matter. For technical reasons it is usually assumed that, after a quench, the far-from equilibrium fields are still spatially uniform. Here we relax this assumption and study the time evolution of a holographic superconductor after a temperature quench but allowing spatial variations of the order parameter amplitude. Even though the initial state and the quench are spatially uniform we show the order parameter develops spatial oscillations with an amplitude that increases with time until it reaches a stationary value for long times. The free energy of these inhomogeneous solutions is lower than that of the homogeneous ones. Therefore the former corresponds to the physical configuration that could be observed experimentally.

 
16:30-17:15 Myers, R (Perimeter Institute for Theoretical Physics)
  Quantum quenches & holography Sem 1
 

We employ holographic techniques to study quantum quenches at finite temperature, where the quenches involve varying the coupling of the boundary theory to a relevant operator with an arbitrary conformal dimension. The evolution of the system is studied by evaluating the expectation value of the quenched operator and the stress tensor throughout the process. The time dependence of the new coupling is characterized by a fixed timescale and the response of the observables depends on the ratio of the this timescale to the initial temperature. The observables exhibit universal scaling behaviours when the transitions are either fast or slow, i.e., when this ratio is very small or very large. For fast quenches, we uncover a universal scaling behaviour in the response of the system, which depends only on the conformal dimension of the quenched operator in the vicinity of the ultraviolet fixed point of the theory.

 
Wednesday 18 September
09:00-09:45 Gauntlett, J (Imperial College London)
  Spatially modulated phases in holography Sem 1
 

Spatially modulated phases are widespread in nature. Holographically they are described by novel black hole solutions. The talk will focus on two topics. The first is some general results on the thermodynamics of periodic black branes. The second is the construction of some new superconducting p-wave and (p+ip)-wave black holes.

 
09:45-10:30 Rozali, M (University of British Columbia)
  Striped order in AdS/CFT Sem 1
 

Co-authors: Darren Smyth (UBC), Evgeny Sorkin (UBC), Jared Stang (UBC)

I discuss the formation of inhomogeneous order in the Einstein-Maxwell-axion system, dual to a 2+1 dimensional field theory that exhibits a spontaneously generated current density, momentum density and modulated scalar operator. Below the critical temperature, the Reissner-Nordstrom-AdS black hole becomes unstable and stripes form in the bulk and on the boundary. The bulk geometry possesses striking geometrical features, including a modulated horizon that tends to pinch off as T goes to 0. The phase transition to the formation of stripes is of second order.

 
10:30-11:00 Morning Coffee
11:00-11:45 Gasenzer, T (Universität Heidelberg)
  Non-thermal fixed points: universality, topology, & turbulence in Bose systems Sem 1
 

Co-authors: Sebastian Erne (Universität Heidelberg, Germany), Markus Karl (Universität Heidelberg, Germany), Boris Nowak (Universität Heidelberg, Germany)

Among the wealth of possible non-equilibrium many-body configurations most interesting candidates are those which show universal behavior. New, non-thermal fixed points are proposed, leading beyond standard equilibrium critical points. A selection of phenomena in ultracold Bose gases, characterized by specific power-laws in space and time, and universal time evolution will be presented. These are, for generic cases, related to the presence and turbulent dynamics of (quasi-)topological defects in the Bose field, which are manifestly far from equilibrium. Examples how to reach these critical points which will be discussed include interaction quenches and rapid evaporative cooling. Our results confirm non-perturbative quantum field theoretical predictions and establish a new link between kinetic wave turbulence and topological excitations of superfluids. They open a path to explore a new class of universal far-from-equilibrium dynamics well accessible in ultracold gas experiment s. These phenomena are of importance far beyond the realm of cold gases and allow a view on new classifications of universal far-from-equilibrium physics.

 
11:45-12:30 Chesler, P (Massachusetts Institute of Technology, Harvard)
  Holographic turbulence Sem 1
 

Co-authors: Hong Liu (MIT), Allan Adams (MIT)

According to holography, turbulent flows in relativistic boundary conformal field theories should be dual to dynamical black hole solutions in asymptotically AdS_{d+2} spacetime with d the number of spatial dimensions the turbulent flow lives in. This immediately raises many interesting questions about gravitational dynamics. For example, what distinguishes turbulent black holes from non-turbulent ones? What is the gravitational origin of energy cascades and the Kolmogorov scaling observed in turbulent fluid flows?

We construct turbulent black holes in asymptotically AdS_4 spacetime by numerically solving Einstein's equations. Both the dual holographic fluid and bulk geometry display signatures of an inverse cascade with the bulk geometry being well approximated by the fluid/gravity gradient expansion. I will argue that statistically steady-state black holes dual to d dimensional turbulent flows have horizons which are approximately fractal with fractal dimension D = d + 4/3. Time permitting I will discuss qualitative differences between holographic superfluid turbulence normal fluid turbulence.

 
12:30-13:30 Lunch at Wolfson Court
14:00-14:45 de Boer, J (Universiteit van Amsterdam)
  Entanglement entropy in higher spin theories Sem 1
 

A holographic correspondence has been recently developed between higher spin theories in three-dimensional anti-de Sitter space (AdS_3) and two-dimensional Conformal Field Theories (CFTs) with extended symmetries. A class of such dualities involves SL(N,R)\times SL(N,R) Chern-Simons gauge theories in the (2+1)-dimensional bulk spacetime, and CFTs with W_N symmetry algebras on the (1+1)-dimensional boundary. The topological character of the Chern-Simons theory forces one to reconsider standard geometric notions such as black hole horizons and entropy, as well as the usual holographic dictionary. Motivated by this challenge, in this note we present a proposal to compute entanglement entropy in the W_N CFTs via holographic methods. In particular, we introduce a functional constructed from Wilson lines in the bulk Chern-Simons theory that captures the entanglement entropy in the CFTs dual to standard AdS_3 gravity, corresponding to SL(2,R)\times SL(2,R) gauge group, and admits an immediate generalization to the higher spin case. We explicitly evaluate this functional for several known solutions of the Chern-Simons theory, including charged black holes dual to thermal CFT states carrying higher spin charge, and show that it reproduces expected features of entanglement entropy, study whether it obeys strong subadditivity, and moreover show that it reduces to the thermal entropy in the appropriate limit.

 
14:45-15:30 Ryu, S (University of Illinois at Urbana-Champaign)
  Effective field theories for topological insulators via functional bosonization Sem 1
 

Effective field theories that describes the dynamics of a conserved U(1) current in terms of “hydrodynamic” degrees of freedom of topological phases in condensed matter are discussed in general dimension D = d+1 using the functional bosonization technique. For non-interacting topological insulators (superconductors) with a conserved U(1) charge and characterized by an integer topological invariant, we derive the BF-type topological field theories supplemented with the Chern-Simons (when D is odd) or the θ-term (when D is even). For topological insulators characterized by a Z2 topological invariant (the first and second descendants of the primary series), their topological field theories are obtained by dimensional reduction. Building on this effective field theory description for noninteracting topological phases, we also discuss, following the spirit of the parton construction of the fractional quantum Hall effect by Block and Wen, the putative “fractional” topological insulators and their possible effective field theories, and use them to determine the physical properties of these.

 
15:30-16:00 Afternoon Tea
16:00-16:45 Kiritsis, E (University of Crete)
  The IR landscape of holography: Cohesive and fractionalised phases, insulators and bad metals. Sem 1
 

Co-authors: Blaise Gouteraux (Nordita), Aristos Donos (Cambridge)

All scaling IR asymptotics in homogeneous, translation invariant holographic phases with a (potentially broken) U(1) symmetry in the IR are classified. The general critical saddle-point solutions are characterized by four critical exponents ($\theta, z$) for the metric as well as the scaling of the electric potential and electric flux . Neutral or charged geometries realizing both fractionalized or cohesive phases are found. In the presence of helical invariance, (breaking translational invariance), new universality classes are possible that correspond to insulators and bad metals.

 
16:45-17:30 Son, DT (University of Chicago)
  Newton-Cartan geometry and the quantum Hall effect Sem 1
 

Co-authors: Siavash Golkar (University of Chicago), Dung Xuan Nguyen (University of Chicago)

We construct an effective field theory for quantum Hall states, guided by the requirements of nonrelativistic general coordinate invariance and regularity of the zero mass limit. We propose Newton-Cartan geometry as the most natural formalism to construct such a theory. Universal predictions of the theory are discussed. We also derived new sum rules for fractional quantum Hall states.

 
19:30-22:00 Conference Dinner at St. Catharine's College
Thursday 19 September
09:00-09:45 Hubeny, V (University of Durham)
  Holographic entanglement plateaux Sem 1
 

Co-authors: Henry Maxfield (Durham), Mukund Rangamani (Durham), Erik Tonni (SISSA)

We discuss holographic entanglement entropy in Lorentzian bulk geometries, contrasting the Ryu-Takayanagi minimal surface prescription with the Hubeny-Rangamani-Takayanagi extremal surface prescription. The former guarantees that entanglement entropy is continuous (though not necessarily differentiable) function of region size. We discuss conditions leading to saturating the Araki-Lieb inequality giving rise to an 'entanglement plateau' and conclude with open questions related to the homology constraint.

 
09:45-10:30 Herzog, C (Stony Brook University)
  Exploring the ABJM Plasma Sem 1
 

I will discuss numeric hydrodynamic and gravity models of the ABJM plasma. In particular, I will explore connections to turbulence and shock waves. I will also discuss some hydrodynamic calculations of momentum loss.

 
10:30-11:00 Morning Coffee
11:00-11:45 Verstrate, F (Universiteit Gent)
  Edge theories in tensor network states Sem 1
11:45-12:30 Swingle, B (Harvard University)
  Entanglement, renormalization, and holography Sem 1
 

The theme of this talk is the interplay between entanglement and renormalization in quantum matter. The goal is to formulate a general conceptual and computational framework for understanding entanglement in quantum matter. I will begin by describing recent progress in computing entanglement properties of interesting ground states by focusing on the low energy physics. My examples will include Fermi liquids, topological states, disordered insulators, and quantum critical points. Then I will discuss how the results of such studies lead us naturally to consider certain classes of tensor network states that incorporate the interplay between entanglement and renormalization. Finally, I will talk about the connections between such tensor network states and holographic duality.

 
12:30-13:30 Lunch at Wolfson Court
14:00-14:45 Headrick, M (Brandeis University)
  What can holographic entanglement entropy teach us about general relativity? Sem 1
 

The covariant holographic entanglement entropy formula proposed by Hubeny, Rangamani, and Takayanagi asserts that the entropy of a boundary region is given by the area of a certain extremal spacelike surface in the bulk. Unlike for more familiar objects like timelike geodesics and horizons, there are not yet many theorems about extremal spacelike surfaces in the general-relativity literature. However, based on considerations from quantum information theory, the HRT formula implies or suggests a large number of interesting general statements about such surfaces and their relation to the spacetime's global causal structure. The effort to prove these novel conjectures has spurred significant recent developments in GR. I will explain the conjectures, their motivation, and the progress that has been made toward proving them.

 
14:45-15:15 Pang, D (Max-Planck-Institut für Physik, München)
  Thermodynamics of entanglement entropy for excited states: some non-conformal examples Sem 1
 

We study thermodynamics of entanglement entropy for excited states of non-conformal branes and observe certain universal behavior of the entanglement temperature.

 
15:15-15:45 Afternoon Tea
15:45-16:15 Hartong, J (University of Copenhagen)
  A Top-Down Model for Lifshitz Holography Sem 1
 

In this talk I will discuss Lifshitz holography for a specific model admitting 4D z=2 Lifshitz space-times that can be uplifted to 5D asymptotically AdS space-times. The model forms a well-behaved low energy limit of type IIB string theory. I will show that the boundary geometry of asymptotically locally Lifshitz space-times is described by Newton-Cartan geometry with in general nonzero torsion. To properly account for all the sources and local symmetries it is very useful to use a Vielbein formalism. Further all deformations of asymptotically locally Lifshitz space-times allowed by the equations of motion are discussed. I will use this to compute the Lifshitz boundary stress energy tensor and derive its Ward identities. I will also show that the 4D Fefferman-Graham expansion has 6+6+1 free functions where 6 are sources and 6 are vevs and where there is one additional free function that does not talk to any of the sources and vevs.

 
16:15-17:00 Kachru, S (Stanford University)
  Wilsonian and large N approaches to non-Fermi liquids Sem 1
 

Co-authors: Liam Fitzpatrick (Stanford), Jared Kaplan (Johns Hopkins), Sri Raghu (Stanford)

We use Wilsonian RG and large N techniques to study the quantum field theory of a critical boson interacting with a Fermi surface, and compare/contrast the results with those coming from holography.

 
Friday 20 September
09:00-09:45 Gubser, S (Princeton University)
  Finite momentum at string endpoints Sem 1
 

Co-authors: Andrej Ficnar (Columbia University)

Classical string solutions exist with finite momentum at endpoints. I will explain the main features of finite endpoint momentum, including an extension of the Green-Schwarz action. Finite endpoint momentum is useful in the study of holographic energy loss by light quarks. I will show how simple analytic methods suffice to extract the main features of the relevant string motions, and I will present some preliminary phenomenological results.

 
09:45-10:30 Schalm, K (Universiteit Leiden)
  Far from equilibrium dynamics in CFTs and holography Sem 1
 

Co-authors: M.J. Bhaseen (King's College), Benjamin Doyon (King's College), Andrew Lucas (Harvard).

Abstract: We investigate far from equilibrium energy transport in strongly coupled quantum critical systems. Combining results from gauge-gravity duality, relativistic hydrodynamics, and quantum field theory, we argue that long-time energy transport occurs via a universal steady-state for any spatial dimensionality. This state can be uniquely identified as a Lorentz boosted thermal state.

 
10:30-11:00 Morning Coffee
11:00-11:45 Yaffe, L (University of Washington)
  Numerical relativity and far-from-equilibrium dynamics Sem 1
 

A variety of gravitational dynamics problems in asymptotically anti-de Sitter (AdS) spacetime are amenable to efficient numerical solution using a common approach involving a null slicing of spacetime based on infalling geodesics, convenient exploitation of the residual diffeomorphism freedom, and use of spectral methods for discretizing and solving the resulting differential equations. After describing the approach, recent results on colliding planar shock waves are presented. The validity of hydrodynamics and the applicability of "local" boost invariance in describing the outgoing flow is examined.

 
11:45-12:30 Lee, SS (McMaster University)
  Quantum renormalization group and holography Sem 1
 

In this talk, I will discuss about the quantum renormalization group and its connection to holography. Via quantum renormalization group procedure, one can show that the holographic dual for an idealized matrix field theory which has no other operator with finite scaling dimension besides the energy-momentum tensor is the Einstein gravity upto two derivative order.

 
12:30-13:30 Lunch at Wolfson Court
14:00-14:45 Erdmenger, JK (Max-Planck-Institut für Physik, München)
  A holographic model of the Kondo effect Sem 1
 

Coauthors: C. Hoyos (Tel Aviv Univ.), A. O'Bannon (DAMTP Cambridge), J. Wu (NCTS Taiwan)

We propose a holographic model of the Kondo effect, i.e. of the screening of a magnetic impurity coupled to a bath of conduction electrons at low temperatures. In a (1+1)-dimensional CFT description, this corresponds to an RG flow from an UV to an IR fixed point triggered by a marginally relevant (0+1)-dimensional operator. In the large N limit, with spin SU(N) and charge U(1) symmetries, the Kondo effect appears as a mean-field phase transition in which the U(1) symmetry is spontaneously broken. Inspired by a top-down brane model, we model the Kondo RG flow by an AdS_3 Chern-Simons action coupled to an AdS_2 holographic superconductor. We observe several characteristic features of the Kondo effect in this model, such as dynamical scale generation and a phase shift. Moreover, we find a power-law behaviour of the resistivity with temperature which is consistent with over-screening. Our model may serve as a basis for investigating more involved problems such as Kondo lattices.

 
14:45-15:15 Goutéraux, B (KTH - Royal Institute of Technology)
  Universal scaling properties of holographic cohesive phases Sem 1
 

Co-author: Kiritsis, Elias (University of Crete)

In this talk, we focus on zero-temperature, strongly-coupled, translation-invariant holographic phases at finite density. We show that they can be classified according to the scaling behavior of the metric, the electric potential and the electric flux. Solutions fall into two classes, depending on whether they break relativistic symmetry or not. We conjecture a universal scaling for the optical conductivity at zero temperature and low frequencies, which reduces to the correct result for both classes of solutions.

 
15:15-15:45 Afternoon Tea
15:45-16:15 Zhang, YL (Chinese Academy of Sciences)
  Petrov type $I$ Spacetime and Dual Hydrodynamics Sem 1
 

Co-authors: Rong-Gen Cai (Institute of Theoretical Physics, Chinese Academy of Sciences), Kostas Skenderis (University of Southampton)

It has been shown that imposing a Petrov type $I$ condition on a $(p+1)$-dimensional timelike hypersurface embedded in a $(p+2)$-dimensional vacuum Einstein gravity reduces the degrees of freedom in the extrinsic curvature of the hypersurface to that of a fluid on the hypersurface. We show that the Relativistic fluid dual to vacuum Einstein gravity does satisfy the covariant Petrov type $I$ condition at least up to second order in derivative expansion. In addition, we show that this procedure can be inversed to derive the relativistic hydrodynamics with higher order corrections through imposing the Petrov type $I$ condition, and that some second order transport coefficients can also be extracted.

Coset model for the Luttinger liquid

 
16:15-17:00 Semenoff, GW (University of British Columbia)
  Quantum hallography Sem 1
 

A new holographic description of defect field theories using probe D5 branes is discussed. We consider a system where a large number of probe branes, which are asymptotically D5 branes blow up into a D7 brane suspended in the bulk of anti-de Sitter space. For a particular ratio of charge density to external magnetic field, so that the Landau level filling fraction is exactly one, the D7 brane exhibits an incompressible, charge gapped state with one unit of integer quantized Hall conductivity. We also show that states with integer filling fractions greater than one are multiple D7 branes. We also see that compressible states can be those of D7 rather than D5 branes and we outline what is known about the phase diagram.

 

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