Gauge / Gravity Duality 2013

Book of Abstracts

(last update: July 31, 2013)

Max Planck Institute for Physics, Munich

29 July to 2 August 2013

Contents

1 Monday 41.1 Sean Hartnoll: Strongly coupled metals and insulators . . . . . . . . . . . . . . . . . . . . 41.2 Elias Kiritsis: The Chern-Simons Diffusion Rate in Holographic QCD . . . . . . . . . . . 41.3 Amos Yarom: Hydrodynamics and anomalies . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Stefan Fredenhagen: Aspects of the higher-spin AdS3/CFT2 correspondence . . . . . . . 41.5 Juan Jottar: Thermal and entanglement entropies in three-dimensional higher spin theories 41.6 Martin Ammon: Wilson Lines and Entanglement Entropy in Higher Spin Gravity . . . . . 41.7 Ben Craps: Inhomogeneous Holographic Thermalization . . . . . . . . . . . . . . . . . . . 51.8 Aleksi Vuorinen: Holographic thermalization at intermediate coupling . . . . . . . . . . . 51.9 David Mateos: Far-from-equilibrium Holography and Heavy Ion Collisions . . . . . . . . . 51.10 Michal P. Heller: Holographic hydrodynamization . . . . . . . . . . . . . . . . . . . . . . . 51.11 Matteo Bertolini: (Super)Current Correlators and Holography . . . . . . . . . . . . . . . . 5

2 Tuesday 52.1 Zoltan Bajnok: Casimir effect and the quark-anti-quark potential . . . . . . . . . . . . . . 52.2 David Tong: Holographic Conductivities in Massive Gravity . . . . . . . . . . . . . . . . . 62.3 Donovan Young: Scattering Amplitudes of Massive N=2 Gauge Theories in Three Dimensions 62.4 Ingo Kirsch: Coset approach to the Luttinger liquid . . . . . . . . . . . . . . . . . . . . . 62.5 Gordon Semenoff: Giant D5 brane holographic quantum Hall states . . . . . . . . . . . . 62.6 Christopher Eling: Conformal anomalies in hydrodynamics . . . . . . . . . . . . . . . . . 62.7 Oriol Pujolas: Emergent Lorentz Invariance from Strong Dynamics . . . . . . . . . . . . . 62.8 Richard Davison: Momentum relaxation in holographic massive gravity . . . . . . . . . . 62.9 Anastasios Taliotis: Extra dimensions, black holes and fireballs at the LHC . . . . . . . . 72.10 Xiaoning Wu: Fluid/Gravity Correspondence For General Non-rotating Black Holes . . . 72.11 Marko Djuric: Vector Meson Production at Low x from Gauge/Gravity Duality . . . . . . 72.12 Yu Tian: Holographic entropy production . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.13 Matti Jarvinen: Holographic models for QCD in the Veneziano limit . . . . . . . . . . . . 72.14 Timo Alho: Thermodynamics of holographic models for QCD in the Veneziano limit . . . 82.15 Jelle Hartong: Sources and Vevs for Lifshitz Holography . . . . . . . . . . . . . . . . . . . 82.16 Javier Tarrio: D3/D7 plasmas at finite temperature and charge density . . . . . . . . . . 82.17 Daniele Musso: Unbalanced Holographic Superconductors: Spintronics and Multiple Or-

derings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.18 Jia-Rui Sun: Novel features of the transport coefficients in Lifshitz black branes . . . . . . 82.19 Alexander Krikun: Holographic model of S± multiband superconductor . . . . . . . . . . 92.20 Francisco Pena-Benitez: New anomaly induced second order transport . . . . . . . . . . . 92.21 Johannes Schmude: Superconformal indices for Sasaki-Einstein backgrounds . . . . . . . . 92.22 Yunseok Seo: Thermal Mass and Plasmino for Strongly Interacting Fermions vis Holography 92.23 Razieh Pourhasan: On Spacetime Entanglement . . . . . . . . . . . . . . . . . . . . . . . 9

3 Wednesday 103.1 Karl Landsteiner: Holographic Type II Goldstone Bosons . . . . . . . . . . . . . . . . . . 103.2 Andreas Karch: Entanglement Entropy for Probe Branes . . . . . . . . . . . . . . . . . . 103.3 Nicholas Evans: Probing Out of Equilibrium Dynamics . . . . . . . . . . . . . . . . . . . . 10

4 Thursday 104.1 John McGreevy: Holographic obstructions to symmetry-preserving regulators . . . . . . . 104.2 Jerome Gauntlett: Spatially modulated phases in holography . . . . . . . . . . . . . . . . 104.3 Kristan Jensen: The holographic dual of an EPR pair (has a wormhole!) . . . . . . . . . . 104.4 Blaise Gouteraux: Properties of holographic cohesive phases . . . . . . . . . . . . . . . . . 104.5 Niels Obers: Elasticity and hydrodynamics of charged black branes . . . . . . . . . . . . . 114.6 Betti Hartmann: Holographic superconductors and superfluids away from the probe limit 114.7 Bartomeu Fiol: Radiation in Conformal Field Theories . . . . . . . . . . . . . . . . . . . . 114.8 Sumit Das: Quantum Quench and Holographic Phase Transitions . . . . . . . . . . . . . . 114.9 Piotr Surowka: Building a holographic liquid crystal . . . . . . . . . . . . . . . . . . . . . 12

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5 Friday 125.1 Tadashi Takayanagi: Holographic Entanglement Entropy of Excited States . . . . . . . . . 125.2 Veronika Hubeny: Causal wedges in AdS/CFT . . . . . . . . . . . . . . . . . . . . . . . . 125.3 Sera Cremonini: Probing the IR of geometries with hyperscaling violation . . . . . . . . . 125.4 Andrew O’Bannon: A Holographic Model of the Kondo Effect . . . . . . . . . . . . . . . . 125.5 Xi Dong: Holographic Entanglement beyond Classical Gravity . . . . . . . . . . . . . . . 125.6 Sang-Jin Sin: Non-spherical collapse in AdS and Early Thermalization in RHIC . . . . . . 135.7 Mukund Rangamani: Effective actions and hydrodynamic transport . . . . . . . . . . . . 135.8 Rene Meyer: A Holographic Model for the Fractional Quantum Hall Effect . . . . . . . . 135.9 Jan Zaanen: Conference summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6 Posters 136.1 Nele Callebaut: Holographic study of magnetically induced QCD effects . . . . . . . . . . 136.2 Somdeb Chakraborty: Holographic quark-antiquark potential in hot, anisotropic Yang-

Mills plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136.3 Amin Faraji Astaneh: Holographic Entanglement Entropy for Excited States in Two Di-

mensional CFT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.4 Antonio Carlos Faria and Claudio Nassif: Gravity and Vacuum Energy from a Universal

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.5 Antonio Carlos Faria: Gravitational Waves from Extra Dimensions . . . . . . . . . . . . . 146.6 Antonio Carlos Faria and Claudio Nassif: Relations between the speed of light, the tem-

perature and the expansion of the Universe . . . . . . . . . . . . . . . . . . . . . . . . . . 156.7 Benedikt Herwerth: Optical Conductivity of Helical Superconductors . . . . . . . . . . . . 156.8 Stefan Janiszewski: Non-relativistic holography . . . . . . . . . . . . . . . . . . . . . . . . 156.9 Yegor Korovin: Lifshitz as a deformation of AdS . . . . . . . . . . . . . . . . . . . . . . . 156.10 Victoria Martin: Entanglement Renyi Entropy via Uniformization of Riemann Surfaces . 156.11 Jiri Minar: Fermi-Hubbard Hamiltonian with non unitary tunnelings: Quantum simulator

of general curved spacetimes with cold atoms . . . . . . . . . . . . . . . . . . . . . . . . . 166.12 Claudio Nassif and Antonio Carlos Faria: Gravity from a universal lower speed regime in

nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.13 Alexander Patrushev: Squashed cones and surface contributions to entanglement entropy. 166.14 Flavio Porri: Holographic R-symmetric flows and the τU conjecture . . . . . . . . . . . . . 176.15 Andreas Samberg: Heavy Probes in Strongly Coupled Plasmas With Chemical Potential . 176.16 Jared Stang: Striped order in AdS/CFT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.17 Stephan Steinfurt: A universal fermionic analogue of the shear viscosity . . . . . . . . . . 176.18 Migael Strydom: Spontaneous lattice ground states from a magnetic field . . . . . . . . . 176.19 Wilke van der Schee: From full stopping to transparency in a holographic model of heavy

ion collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.20 Jackson Wu: A Holographic Model of the Kondo Effect . . . . . . . . . . . . . . . . . . . 186.21 Hansjorg Zeller: Transport Properties of Holographic P-Wave Superfluids . . . . . . . . . 18

7 Acknowledgments 18

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1 Monday

1.1 Sean Hartnoll: Strongly coupled metals and insulators

Holography is a fantastic tool for doing controlled calculations in strongly coupled theories. However, inorder to know what to compute and how these results fit into a century of condensed matter physics, it isnecessary to understand clearly the essential aspects of quantum field theory at finite charge density. Thistalk is about the effective field theory description of metals and insulators. I will explain how holographyhas led to new ways of thinking about what it means to be a metal or an insulator.

1.2 Elias Kiritsis: The Chern-Simons Diffusion Rate in Holographic QCD

In (3 + 1)-dimensional SU(Nc) Yang-Mills (YM) theory, the Chern-Simons diffusion rate, ΓCS , is de-termined by the zero-momentum, zero-frequency limit of the retarded two-point function of the CP-oddtopological operator tr[F ∧F ], with F the YM field strength. The Chern-Simons diffusion rate is a crucialingredient for many CP-odd phenomena, including the chiral magnetic effect in the quark-gluon plasma.We compute ΓCS in the high-temperature, deconfined phase of Improved Holographic QCD, a refinedholographic model for large-Nc YM theory. Our result for ΓCS/(sT), where s is entropy density and T istemperature, varies slowly at high T and increases monotonically as T approaches the transition temper-ature from above. We also study the retarded two-point function of tr[F ∧ F ] with non-zero frequencyand momentum. Our results suggest that the CP-odd phenomena that may potentially occur in heavyion collisions could be controlled by an excitation with energy on the order of the lightest axial glueballmass.

1.3 Amos Yarom: Hydrodynamics and anomalies

After reviewing the role of anomalies in the hydrodynamic behavior of gauge theory fluids I will discussthe construction of a master function whose derivatives give the anomalous contribution to the currentand stress-tensor (for a hydrostatic configuration) in any dimension and in any order in the derivativeexpansion.

1.4 Stefan Fredenhagen: Aspects of the higher-spin AdS3/CFT2 correspondence

In three space-time dimensions, higher-spin gauge fields are particularly simple, because they do not havepropagating degrees of freedom. Nevertheless higher-spin gravity theories have a rich structure, and theyprovide an interesting setup to study AdS/CFT duality. I will review the developments of the past yearswith a focus on the asymptotic symmetries, which play a crucial role in the higher-spin AdS3/CFT2correspondence.

1.5 Juan Jottar: Thermal and entanglement entropies in three-dimensional higherspin theories

A holographic correspondence has been recently developed between higher spin theories in AdS3 and(1+1)-dimensional CFTs with extended symmetries. In this framework, black hole solutions in the bulktheory are dual to thermal equilibrium states with non-trivial higher spin charges and chemical potentials.We discuss the calculation of the higher spin black hole entropy from an appropriate Euclidean variationalprinciple, and provide a generalization of the Cardy entropy formula for these setups. Additionally, wepresent a proposal to compute entanglement entropy in the dual CFTs via holography, thus extendingthe Ryu-Takayanagi prescription to higher spin theories in AdS3.

1.6 Martin Ammon: Wilson Lines and Entanglement Entropy in Higher SpinGravity

Holographic entanglement entropy provides a direct connection between classical geometry and quantumentanglement; however the usual prescription does not apply to theories of higher spin gravity, wherestandard notions of geometry are no longer gauge invariant. We present a proposal for the holographiccomputation of entanglement entropy in field theories dual to higher spin theories of gravity in AdS3.

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These theories have a Chern-Simons description, and our proposal involves a Wilson line in an infinite-dimensional representation of the bulk gauge group. In the case of spin-2 gravity such Wilson lines arethe natural coupling of a heavy point particle to gravity and so are equivalent to the usual prescriptionof Ryu and Takayanagi. For higher spin gravity they provide a natural generalization of these ideas. Wework out spin-3 gravity in detail, showing that our proposal recovers many expected results and computesthermal entropies of black holes with higher spin charge, finding agreement with previous expressions inthe literature.

1.7 Ben Craps: Inhomogeneous Holographic Thermalization

The sudden injection of energy in a strongly coupled conformal field theory and its subsequent thermal-ization can be holographically modeled by a shell falling into anti-de Sitter space and forming a blackbrane. Motivated by event-by-event fluctuations in heavy ion collisions, the inclusion of inhomogeneitiesin such a model is discussed. The resulting early-time evolution is compared with free streaming andwith viscous hydrodynamics.

1.8 Aleksi Vuorinen: Holographic thermalization at intermediate coupling

I will review some progress made recently in the description of a thermalizing N=4 Super Yang-Millsplasma, working in the limit of large, but not infinite ’t Hooft coupling. Special attention will be paid tothe evaluation of off-equilibrium Green’s functions of the energy momentum tensor and an external U(1)gauge field, as well as the pattern with which these quantities approach their respective thermal limits.Based on the results, I will argue that the usual top/down pattern of holographic thermalization weakenssignificantly, as one leaves the limit of infinite coupling.

1.9 David Mateos: Far-from-equilibrium Holography and Heavy Ion Collisions

I will review applications of the gauge/string duality to the description of the far-from-equilibrium, earlystage of heavy ion collisions.

1.10 Michal P. Heller: Holographic hydrodynamization

I will discuss recent progress in understanding how and when hydrodynamics becomes applicable inholographic non-equilibrium setups. In particular, I will show that contrary to the common lore, hydro-dynamics alone contains also information about far from equilibrium degrees of freedom.

1.11 Matteo Bertolini: (Super)Current Correlators and Holography

We discuss general properties of correlators of operators belonging to conserved current and supercurrentmultiplets in four-dimensional supersymmetric quantum field theories. We focus on strongly coupledtheories, and use holography to compute several such correlators, discussing the different informationthat can be extracted from them. We focus on models where global symmetries, supersymmetry orconformal symmetry are spontaneously broken, and discuss few applications, including gauge mediationmodels.

2 Tuesday

2.1 Zoltan Bajnok: Casimir effect and the quark-anti-quark potential

The Casimir effect is the manifestation of the quantum nature of the vacuum. It formulates how theground state energy depends on the separation of the dielectric plates, and is usually calculated bysumming up the zero mode frequencies. Alternatively, it can be described in terms of the reflections ofvirtual particles, which can be exactly calculated in integrable theories. Applying these ideas to planarAdS/CFT, integral equations for the quark-anti-quark potential can be derived. By expanding theseintegral equations at NLO the two loop gauge theory calculation can be confirmed.

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2.2 David Tong: Holographic Conductivities in Massive Gravity

Massive gravity is dual to a boundary theory with momentum dissipation. I’ll describe various aspectsof transport in this framework.

2.3 Donovan Young: Scattering Amplitudes of Massive N=2 Gauge Theories inThree Dimensions

I will discuss the tree-level four particle scattering amplitudes of mass-deformed N=2 Chern-Simons theory(CSM) and N=2 Yang-Mills-Chern-Simons theory (YMCS). The on-shell SUSY algebras for these theoriesgreatly constrain the amplitudes, and allow, in the case of CSM, for a compact superamplitude expression.I will also discuss BCFW recursion for massive theories in three-dimensions and its applicability to CSMand YMCS.

2.4 Ingo Kirsch: Coset approach to the Luttinger liquid

I discuss matrix coset conformal field theories of the type (SU(N)N x SU(N)N )/SU(N)2N . These CFTsplay a role in the description of the Luttinger liquid at high densities.

2.5 Gordon Semenoff: Giant D5 brane holographic quantum Hall states

A new holographic description of strongly coupled 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, blowup into a D7 brane suspended in the bulk of anti-de Sitter space. For a particular ratio of charge densityto external magnetic field, so that the Landau level filling fraction per color is equal to one, the D7 braneexhibits an incompressible charge-gapped state with one unit of integer quantized Hall conductivity. Thedetailed configuration as well as ungapped, compressible configurations for a range of parameters nearthe gapped one are found by solving the D5 and D7 brane embedding equations numerically and the D7is shown to be preferred over the D5 by comparing their energies. We then find integer quantum Hallstates with higher filling fractions as a stack of D5 branes which blow up to multiple D7 branes whereeach D7 brane has filling fraction one.

2.6 Christopher Eling: Conformal anomalies in hydrodynamics

I will discuss the effect of conformal anomalies on the hydrodynamic description of finite temperatureconformal field theories in even spacetime dimensions. We consider equilibrium curved backgroundscharacterized by a time-like Killing vector and construct a local low energy effective action that capturesthe conformal anomalies. Using this action I will show how the anomaly contributes to the hydrodynamicpressure and to the thermal entropy, which is equivalent in some contexts to an entanglement entropy.

2.7 Oriol Pujolas: Emergent Lorentz Invariance from Strong Dynamics

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

2.8 Richard Davison: Momentum relaxation in holographic massive gravity

I will discuss the idea of using massive gravity as a way to incorporate the dissipation of momentum ina holographic theory. For a simple massive gravity model, I will describe how one should modify hydro-dynamics in the field theory to account for this dissipation of momentum and compute the characteristictimescale over which momentum dissipates in terms of the graviton mass. I will show that for smallgraviton masses and frequencies, the conductivity of the field theory is that of the simple Drude model,and I will determine the corrections to this which are important for larger masses and frequencies.

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2.9 Anastasios Taliotis: Extra dimensions, black holes and fireballs at the LHC

The collision of two gravitationally interacting, ultra-relativistic, extended sources is being examined.This investigation classifies the transverse distributions that are collided according to whether one or two(a small and a large) apparent horizons may or may not be formed in a flat background in 4 dimensions.The study suggests a universal behavior in the produced entropy and, the elimination of the possibility inobserving black holes (BHs) at the LHC in the absence of extra dimensions. On the other hand, includingextra dimensions, and assuming that the matter is localized (dense) enough in those directions, opensnew avenues in creating BHs at TeV scales.

The investigation is carried further to AdS5 backgrounds and makes connections with QGP. In particu-lar, it seems that a BH is formed if and only if the (central collision) energy is sufficiently large comparedto the transverse scale of the corresponding gauge theory side stress-tensor. This implies that a result,which is in accordance with the current intuition and data: QGP is formed only at high enough energiescompared to ΛQCD, even for central processes. Incorporating weak coupling physics and in particularthe Color Glass Condensate (CGC) model, a satisfactory fitting with the RHIC and the LHC data formultiplicities may be established.

2.10 Xiaoning Wu: Fluid/Gravity Correspondence For General Non-rotating BlackHoles

In this paper, we investigate the fluid/gravity correspondence in spacetime with general non-rotatingweakly isolated horizon. With the help of Petrov-like boundary condition and large mean curvaturelimit, we show that the dual hydrodynamical system is described by a generalized forced incompressibleNavier-Stocks equation. Specially, for stationary black holes or those spacetime with some asymptoticallystationary conditions, such a system reduces to a standard forced Navier-Stocks system.

2.11 Marko Djuric: Vector Meson Production at Low x from Gauge/GravityDuality

We use gauge/gravity duality to study vector meson production in the limit of high center of mass energyat fixed momentum transfer, corresponding to the limit of low Bjorken x, where the process is dominatedby the exchange of the pomeron. At strong coupling, the pomeron is described by the graviton Reggetrajectory in AdS space, with a hard wall to mimic confinement effects. We use a simple holographicmodel of the vector meson wave functions in AdS. This model agrees with HERA H1 data with a χ2

per degree of freedom below 1 on the total cross-sections, and below 2 on the differential cross sections,confirming the success of previous studies that model low x DIS and DVCS using gauge/gravity duality.

2.12 Yu Tian: Holographic entropy production

The suspicion that gravity is holographic has been supported mainly by a variety of specific examplesfrom string theory. This talk is intended to purport the holographic gravity from a different perspective.Namely we propose that such a holography can actually be observed within the context of Einstein’sgravity, where neither is space-time required to be asymptotically AdS nor the boundary to be locatedat conformal infinity, echoing Wilson’s profound formulation of quantum field theory. We show thatour holography works remarkably well at least at the level of thermodynamics and hydrodynamics. Inparticular, a perfect matching between the bulk gravity and boundary system is found not only for theequilibrium variation but also for the non-equilibrium entropy production.

2.13 Matti Jarvinen: Holographic models for QCD in the Veneziano limit

I discuss holographic bottom-up models for QCD in the Veneziano limit (large Nf and Nc with fixedx = Nf/Nc). The models are constructed by putting together holographic models of Yang-Mills theory(improved holographic QCD) with Sen-type tachyon actions inspired by brane constructions, and byconsidering full backreaction. At zero temperature and quark mass the phase diagram, as a functionof x = Nf/Nc, meets the expectations from QCD. One finds a ”conformal phase transition” at x = xcfrom a QCD-like regime to the conformal window. The whole spectrum obeys Miransky scaling and theS-parameter approaches a finite positive value as x→ xc from below.

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2.14 Timo Alho: Thermodynamics of holographic models for QCD in theVeneziano limit

We have studied the thermodynamics of a class of holographic bottom-up models for QCD in theVeneziano limit. We find a rich pattern of stable and metastable phases, depending on the choice ofthe phenomenological potentials needed to fully define the model. Generically there is a hadronizationtransition at some temperature, and a chiral symmetry restoring transition which may coincide with thehadronization transition, depending on the choice of potentials. In addition we find a number of moreexotic transitions. Computing the full phase diagram in the (Nf/Nc, T) plane and requiring consis-tency with known features of QCD -like theories, we are able to select among the potentials a preferredcandidate for modeling QCD. Using that potential, we have also studied the effects of a finite chemicalpotential.

2.15 Jelle Hartong: Sources and Vevs for Lifshitz Holography

In this talk I will discuss the properties of the sources and vevs in a near boundary expansion of a 4D z=2asymptotically locally Lishitz space-time. The model used can be uplifted to 5D asymptotically locallyAdS space-times and forms a well-behaved low energy limit of type IIB string theory. The reduction issuch that everywhere in the bulk the circle is spacelike with a size that can be made large with respect tothe string length while retaining low curvatures and weak string coupling yet on the boundary the circleis null. After fixing all local symmetries acting on the sources and using the associated Ward identitiesthe 5D theory has 7+7 sources and vevs. The reduction reduces this to 6+6. To properly account for thesources and local symmetries it is mandatory to use a Vielbein formalism and to allow for all irrelevantdeformations of asymptotically locally Lifshitz space-times. I will show that the boundary values of the4D Vielbeins transform under the contracted Lorentz group and that consequently there is no Lorentzianboundary geometry. The boundary stress-energy tensor is defined as the unique gauge invariant (1,1)tensor that is also invariant under local tangent space transformations. It does not satisfy a conservationequation but by contracting it with a vector that in some appropriate sense is Killing conserved currentscan be constructed. This stress-energy tensor satisfies the expected z=2 trace Ward identity with a scaleanomaly term that contains two central charges. Applications of these methods to Lifshitz holographywill also be discussed.

2.16 Javier Tarrio: D3/D7 plasmas at finite temperature and charge density

I will consider a deformation of N=4 SYM theory, with the addition of a large number of fields trans-forming in the fundamental representation (flavors) at finite charge density and temperature. Having thephase diagram of QCD in mind, I will comment on instabilities and issues at low values of the temperaturecompared to the charge density.

2.17 Daniele Musso: Unbalanced Holographic Superconductors: Spintronics andMultiple Orderings

The holographic unbalanced superconductors are versatile toy models offering the possibility of studyingquantitatively many physical features at strong coupling; among these the most interesting are the mixedspin-electric transport properties and the rich phase diagrams with particular attention on the possibilityof coexisting, mutually competing/enhancing orderings. Interestingly, the applicability of the minimalunbalanced holographic superconductor and its generalizations ranges from condensed matter to QCD-likecontexts. In the former case, some relevant topics which can be investigated by means of the unbalancedholographic superconductors are (among others) the possibility of inhomogeneous FFLO phases at strongcoupling, spintronic response, ferromagnetic/antiferromagnetic superconductors. In this talk we mean totake stock of the results obtained so far and describe the scenario of future perspectives.

2.18 Jia-Rui Sun: Novel features of the transport coefficients in Lifshitz blackbranes

We study the transport coefficients, including the conductivities and shear viscosity of the non-relativisticfield theory dual to the Lifshitz black brane with multiple U(1) gauge fields by virtue of the gauge/gravity

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duality. Focusing on the case of double U(1) gauge fields, we systematically investigate the electric,thermal, and thermoelectric conductivities for the dual nonrelativistic field theory. In the large frequencyregime, we find a nontrivial power law behavior in the electric alternating current conductivity when thedynamical critical exponent z > 1 in (2+1)-dimensional field theory. The relations between this novelfeature and the “symmetric hopping model” in disordered solids are discussed. In addition, we also showthat the Kovtun-Starinets-Son bound for the shear viscosity to the entropy density is not violated by theadditional U(1) gauge fields and dilaton in the Lifshitz black brane.

2.19 Alexander Krikun: Holographic model of S± multiband superconductor

We construct the holographic model of S± multiband superconductor. This system is a candidate toexplain the anomalous features of the iron-based superconductors (e.g. LaFeAsO, BFe2As2, and otherpnictides and arsenides). We study the framework which allows the formation of the sign-interchangingorder parameter. We also calculate the electric AC conductivity and study its features, related to theinterband interaction.

2.20 Francisco Pena-Benitez: New anomaly induced second order transport

Anomalies give rise to new non-dissipative transport coefficient such as the chiral magnetic and chi-ral vortical conductivity. In particular mixed gauge-gravitational anomaly plays an unexpected role insuch conductivities. Using the Fluid/Gravity correspondence we have computed the anomaly inducedsecond order transport for a holographic model that implements both the pure gauge and mixed gauge-gravitational anomalies.

2.21 Johannes Schmude: Superconformal indices for Sasaki-Einstein backgrounds

I will discuss the gravity calculation of the superconformal index of three-dimensional N=2 gauge theoriesdual to M2-branes at Calabi-Yau singularities. This involves the derivation of the spectrum of shortKaluza-Klein multiplets from the geometry of the dual Sasaki-Einstein manifold. One finds that theshort multiplets correspond to Kohn-Rossi cohomology groups and the index takes the form of a sumover these.

The talk is based on 1305.3547 and 1207.0573 (with Richard Eager and Yuji Tachikawa).

2.22 Yunseok Seo: Thermal Mass and Plasmino for Strongly Interacting Fermionsvis Holography

We investigate fermion self energy problem in the strongly coupled dense medium in holographic approach.By working out bottom up models as well as top down ones we showed that vanishing thermal mass andnon-existence of temperature generated plasmino mode is the universal feature of the strongly interactingfermion system. We identified that the dual of the bulk Rashiba effect, which was recently found by theHerzog et.al, is the presence of the plasmino mode generated by the density.

2.23 Razieh Pourhasan: On Spacetime Entanglement

We examine the idea that in quantum gravity, the entanglement entropy of a general region should befinite and the leading contribution is given by the Bekenstein-Hawking area law. Using holographic en-tanglement entropy calculations, we show that this idea is realized in the Randall-Sundrum II braneworldfor sufficiently large regions in smoothly curved backgrounds. Extending the induced gravity action onthe brane to include the curvature-squared interactions, we show that the Wald entropy closely matchesthe expression describing the entanglement entropy. The difference is that for a general region, the latterincludes terms involving the extrinsic curvature of the entangling surface, which do not appear in theWald entropy. We also consider various limitations on the validity of these results.

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3 Wednesday

3.1 Karl Landsteiner: Holographic Type II Goldstone Bosons

The Goldstone theorem implies the appearance of an ungapped mode whenever a continuous globalsymmetry is spontaneously broken. In general it does not say anything about the precise form of thedispersion relation nor does it imply that there is one massless mode for each broken symmetry gener-ator. It is a well-established fact that even for relativistic field theories in the presence of a chemicalpotential Goldstone modes with quadratic dispersion relation, the type II Goldstone bosons, appear inthe spectrum. We develop two holographic models that feature type II Goldstone modes as part of thequasinormal mode spectrum and discuss their properties.

3.2 Andreas Karch: Entanglement Entropy for Probe Branes

We give a prescription for calculating the entanglement entropy in holographic probe brane systems. Afew simple examples are discussed in order to validate the method.

3.3 Nicholas Evans: Probing Out of Equilibrium Dynamics

AdS/CFT allows the relatively simple computation of time dependent phenomena in strongly coupledgauge theories. Introducing matter with probe branes and studying their time dependent dynamicssimplifies the computations further since the gravitational background remains constant. I discuss severalexamples. The D3/D7 system develops a mass gap in the presence of a magnetic field at zero temperature.The finite temperature transition is first order - a time dependent computation as the temperatureincreases can track the transition revealing some of the dynamics of bubble formation. The same systemcan be quenched by changing B resulting in oscillatory or damped evolution depending on parameters.Similar models describe chiral symmetry breaking in gauge theories with running couplings and one canstudy the roll from non-equilibrium configurations to the true vacuum. Walking gauge theories generatea flat effective potential and may be useful as inflationnary models without fundamental scalars.

4 Thursday

4.1 John McGreevy: Holographic obstructions to symmetry-preserving regulators

Certain states of matter in D+1 dimensions, called symmetry-protected topological (SPT) states, canbe completely characterized by their edge excitations in D dimensions. The existence of nontrivial suchstates implies obstructions to intrinsically D-dimensional local realizations of those edge excitations. Theresulting constraints on symmetry-preserving regulators of quantum field theory generalize the Nielsen-Ninomiya results on fermion doubling.

4.2 Jerome Gauntlett: Spatially modulated phases in holography

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

4.3 Kristan Jensen: The holographic dual of an EPR pair (has a wormhole!)

Recently, Maldacena and Susskind conjectured that EPR pairs and non-traversable wormholes describethe same physics. I will discuss a simple holographic example which supports their claim.

4.4 Blaise Gouteraux: Properties of holographic cohesive phases

In this talk, we focus on zero-temperature phases of strongly-coupled holographic superfluids at finitedensity. We show that they can be classified according to their scaling symmetries, as well as thebehavior of the electric flux in the deep IR. In the presence of a running scalar, these phases maydisplay hyperscaling violation. The IR behavior of the electric flux can be captured by introducing a new

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‘cohesion’ exponent and allows to distinguish between fractionalized (constant flux, charged horizon) andcohesive phases (vanishing flux, charged matter in the bulk). It also measures the departure of the electricpotential from exact Lifshitz scaling: the cohesion exponent plays for the gauge field a role similar to thehyperscaling violation exponent for the metric. In particular, in the absence of hyperscaling violation, itallows to distinguish between Lifshitz phases with a running scalar (fractionalized) or a massive vector(cohesive). The electric flux provides a refined order parameter for fractionalization analogous to theWilson loop for confinement. Evaluating it through a bulk minimal surface (determined by the Ryu-Takayanagi or the Hartnoll-Radicevic prescription), we show that its scaling is controlled by the sign ofthe cohesion exponent.

4.5 Niels Obers: Elasticity and hydrodynamics of charged black branes

In the long-wave length regime, charged black branes behave like any other type of continuous media,with their dynamics governed by an effective theory. I will discuss recent insights into this effective theory,using the blackfold approach. In particular, I will show that asymptotically flat charged black branesof supergravity have both elastic and hydrodynamic properties, which can be obtained by consideringextrinsic and intrinsic perturbations respectively. As a consequence, one can determine new (first order)response coefficients of large classes of charged black branes, including the Young modulus and piezoelectric moduli along with hydrodynamic transportcoefficients. I will also comment on relations andpossible applications to the AdS fluid/gravity correspondence.

4.6 Betti Hartmann: Holographic superconductors and superfluids away from theprobe limit

Recently, the gauge/gravity duality has been used to describe so-called holographic superconductors andsuperfluids with the help of black holes and solitons in Anti-de Sitter space-time. In this talk, I will mainlydiscuss holographic superconductors and superfluids away from the probe limit, i.e. taking backreactionof the space-time into account. I will demonstrate that this leads to some important changes in thequalitative and quantitative features.

4.7 Bartomeu Fiol: Radiation in Conformal Field Theories

We study radiation by a heavy probe coupled to a general four-dimensional conformal field theory,and argue that a variety of interesting quantities are determined in terms of a single function, theBremsstrahlung function, that depends on the probe and on the theory. For the particular case of a heavyquark coupled to N=4 super Yang Mills, we use localization techniques to determine the correspondingBremsstrahlung function exactly.

4.8 Sumit Das: Quantum Quench and Holographic Phase Transitions

We investigate quantum quench across holographic phase transitions at finite chemical potential and atzero as well as non-zero temperature. In the field theory this involves a time dependent coupling whichasymptotes to constant values at early and late times and passes through an equilibrium critical point.Staring with the equilibrium state in a gapped phase the aim is to find out properties of the final state. Ithas long been expected that the final state carries universal signatures of the critical point, e.g. Kibble-Zurek scaling - but this is hard to investigate directly in a strongly coupled theory. In the holographicsetup quench corresponds to a time dependent boundary condition of a bulk field. The models we studyinvolve self-coupled bulk scalars in suitable asymptotically AdS backgrounds with gauge fields, whichmay be treated in a probe approximation when this self-coupling is large. For a time dependence which isslow compared to the initial gap, we study the breakdown of adiabatic evolution as the critical region isapproached. We find, however, that in the critical region there is a new small rate expansion in fractionalpowers of the rate. In this expansion, a zero mode of the bulk field dominates the dynamics and leadsto, among other things, Kibble-Zurek scaling. For quench across a model of zero temperature superfluidtransition we find that the dynamical critical exponent which governs the dynamics of the order parameteris z=2, though the dynamics is non-dissipative.

This work is based on arXiv:1109.3909 (JHEP 1201 (2012) 103), arXiv:1211.7076 and ongoing work.

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4.9 Piotr Surowka: Building a holographic liquid crystal

I will present preliminary results how to construct a holographic model with an anisotropic spin twocondensate. Moreover I will give an interpretation of this model as a description of liqid crystals. Futureresearch directions will be sketched.

5 Friday

5.1 Tadashi Takayanagi: Holographic Entanglement Entropy of Excited States

We will explain our recent works on the holographic entanglement entropy. We especially focus on theentanglement entropy of excited states in conformal field theories.

5.2 Veronika Hubeny: Causal wedges in AdS/CFT

The AdS/CFT correspondence has propelled AdS black holes into prominence as useful calculational toolin diverse branches of physics, but it also holds great potential for answering long-standing questions inquantum gravity by recasting them in non-gravitational language. The prerequisite for this program isgood understanding of the dictionary between the two sides, which motivates the present exploration.We study the properties of a very natural gravitational construct – the causal wedge in AdS, pertainingto a specified spatial region on the AdS boundary – in order to obtain insight into its CFT dual. Theconstruction is reminiscent of, but importantly distinct from, the correspondence between CFT entan-glement entropy and area of extremal surface in AdS. After reviewing the causal wedge construction, Iwill discuss interesting global properties of causal wedges in general time-dependent backgrounds, andmention implications for the entanglement entropy.

5.3 Sera Cremonini: Probing the IR of geometries with hyperscaling violation

Geometries which exhibit anisotropic scalings have served as a lholographic aboratory for modeling anumber of condensed matter systems. In this talk I will focus on geometries which realize non-relativisticscaling and hyperscaling violation. In particular, I will explore their behavior in the far infrared, andcomment on potential instabilities of these systems to spatially modulated phases.

5.4 Andrew O’Bannon: A Holographic Model of the Kondo Effect

The Kondo effect occurs in metals doped with magnetic impurities: in the ground state an electronbinds to each impurity, leading to dramatic changes in the thermodynamic and transport properties ofthe metal. Although the single-impurity Kondo effect is considered a solved problem, many questionsremain, 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 poorlyunderstood. In this talk I will present a new model of the single-impurity Kondo effect based on holog-raphy, also known as gauge-gravity duality or the Anti-de Sitter/Conformal Field Theory (AdS/CFT)Correspondence, which may serve as a foundation for a new approach to the multiple-impurity system.

5.5 Xi Dong: Holographic Entanglement beyond Classical Gravity

The Renyi entropies and entanglement entropy of 1+1 CFTs with gravity duals can be computed byexplicit construction of the bulk spacetimes dual to branched covers of the boundary geometry. Atthe classical level in the bulk this has recently been shown to reproduce the conjectured Ryu-Takayanagiformula for the holographic entanglement entropy. We study the one-loop bulk corrections to this formula.The functional determinants in the bulk geometries are given by a sum over certain words of generatorsof the Schottky group of the branched cover. For the case of two disjoint intervals on a line we obtainanalytic answers for the one-loop entanglement entropy in an expansion in small cross-ratio. Thesereproduce and go beyond anticipated universal terms that are not visible classically in the bulk. We alsoconsider the case of a single interval on a circle at finite temperature. At high temperatures we showthat the one-loop contributions introduce expected finite size corrections to the entanglement entropy

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that are not present classically. At low temperatures, the one-loop corrections capture the mixed natureof the density matrix, also not visible classically below the Hawking-Page temperature.

5.6 Sang-Jin Sin: Non-spherical collapse in AdS and Early Thermalization in RHIC

In the flat space, it is well known that non-spherical shell collapses to give globular cluster after manyoscillations. However, we show that in anti de sitter space, arbitrary shape of shell or cloud falls to forma black hole in one dynamical time. By gague/gravity dualuty, this explains the early thermalization instrong quark-gluon plasma. This is traced back to the a remarkable property of AdS : the period in radialmotion is the amplitude independent of the amplitude in spite of the NON-linearity of the equation ofmotion. We investigated the interaction effect numerically and observed the same qualitative behaviorfor the attractive forces. For repulsive interactions, particles halt in the sky for long time due to thespecific structure of the propagator. It may be responsible for the hair creation in the AdS black hole.

5.7 Mukund Rangamani: Effective actions and hydrodynamic transport

I will review some recent progress in constraining hydrodynamic transport using effective actions andcontrast this with standard techniques which demand the presence of a positive divergence entropycurrent. Focussing, on the simple class of non-dissipative fluids I will describe how the effective actioncan help in understanding transport phenomena induced by parity breaking and anomalies.

5.8 Rene Meyer: A Holographic Model for the Fractional Quantum Hall Effect

As has become clearer and clearer in the last two decades, the physics of electrons in strong magneticfields which gives rise to fractional quantum Hall states, seems to be governed by an action of a subgroupof the modular group, Γ0(2). After a general introduction to modular invariance in fractional quantumhall physics, I will present a holographic bottom-up model which realizes a larger group, SL(2,Z), onFQH states. I will furthermore describe important properties of these holographic FQH states, and inparticular show that they are gapped. Finally I will discuss progress in breaking the SL(2,Z) invariance(which is a approximate symmetry in the actual quantum Hall data), in building a model with the smallergroup Γ0(2), and in describing the quantum Hall plateaux transitions holographically.

5.9 Jan Zaanen: Conference summary

A summary of the talks at the conference.

6 Posters

6.1 Nele Callebaut: Holographic study of magnetically induced QCD effects

In the presence of strong magnetic fields the QCD vacuum may become unstable towards condensationof charged rho mesons, forming a superconducting state. We investigated this possible instability in awell-known holographic QCD model called the Sakai-Sugimoto model, using 2 flavours and taking intoaccount the chiral magnetic catalysis effect. Rho meson condensation occurs in this model at very highvalues of the magnetic field, eB ∼ 0.8 GeV2, possibly present during the cosmological electroweak phasetransition or in heavy ion collisions at the LHC. Using the same model in the deconfined phase, wealso investigated the Sakai-Sugimoto prediction for a possible magnetically induced split between chiralrestoration and deconfinement temperature. The discussed results are based on the papers 1105.2217,1303.5674 and work in progress.

6.2 Somdeb Chakraborty: Holographic quark-antiquark potential in hot,anisotropic Yang-Mills plasma

Using the gauge/gravity duality we calculate the heavy quark-antiquark potential in a hot, anisotropic andstrongly coupled Yang-Mills plasma in (3+1)-dimensions. As the anisotropic medium we take a deformedversion of N = 4 super Yang-Mills theory at finite temperature following a recent work where the dualtype IIB supergravity solution is also proposed. We turn on a small value of the anisotropy parameter,

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for which the gravity dual is known analytically (perturbatively), and compute the velocity-dependentquark-antiquark interaction potential when the pair is moving through the plasma with a velocity v. Bysetting v = 0 we recover the static quark-antiquark potential. We numerically study how the potential ismodified in the presence of anisotropy. We further show numerically how the quark-antiquark separation(both in the static and the velocity-dependent case) and hence, the screening length gets modified byanisotropy. We discuss various cases depending upon the direction of the dipole and the direction ofits propagation and make a comparative study of these cases. We are also able to obtain an analyticalexpression for the screening length of the dipole moving in a hot, anisotropic plasma in a special case.

6.3 Amin Faraji Astaneh: Holographic Entanglement Entropy for Excited States inTwo Dimensional CFT

We use holographic methods to study the entanglement entropy for excited states in a two dimensionalconformal field theory. The entangling area is a single interval and the excitations are produced by inand out vertex operators with given scaling dimensions. On the gravity side we provide the excitationsby turning on a scalar field with an appropriate mass. The calculation amounts to using the gravitationalbackground, with a singular boundary, to find the one point function of the vertex operators. The singularboundary is taken care of by introducing a nontrivial UV regulator surface to calculate gravitationalpartition functions. By means of holographic methods we reproduce the field theory results for primaryexcitations.

6.4 Antonio Carlos Faria and Claudio Nassif: Gravity and Vacuum Energy from aUniversal Background

The interest of this work is to analyze the divergence of the vacuum energy and show that this obstaclecan be overcome by a suitable metric that preserves the Lorentz covariance. We show that it is possibleto remove the divergence of the vacuum energy through a universal background and attached to it a andinvariant minimum speed universal and invariant V. Considering the dispersion relation from this metricwe obtain a finite value for the vacuum energy, considering 4-dimensional space-time. This analysis canbring several implications for the understanding of gravity in the relations between gauge theories andstring theories and in the exploration of aspects of the gauge/gravity duality.

6.5 Antonio Carlos Faria: Gravitational Waves from Extra Dimensions

Braneworld scenarios wherein the observable universe is trapped on a brane, embedded in some higherdimensional spacetime, can explain the hierarchy problem. Braneworld models also provide alternativesto Kaluza-Klein compactification, where the topology has a compactification radius of the Planck lengthorder. These possibilities come from developments in non-perturbative string theory, wherein the so-called D-branes are elicited and evinced as (D + 1)-dimensional manifolds in which the standard modelof particles and fields can be con- sistently confined. A plausible reason for the weak appearance ofthe gravitational force, with respect to other forces, can be its dilution in a higher-dimensional bulk,where D-branes are embedded. D-branes are good candidates for braneworlds because among some out-standing features they possess gauge symmetries. The gauge symmetry arises from open strings, whichcan collide to form a closed string which simplest excita- tion modes correspond precisely to gravitons thatcan leak into a higher-dimensional bulk. The possibility con- cerning the existence of extra dimensionsmay still ascer- tain physical aspects on string theory and D-branes. An alternative approach to theextra dimension compactification was pointed by Randall-Sundrum braneworld formalism, where theelectromagnetic, weak, and strong forces, together with all the matter in the universe as well are confinedon a 3-brane, and only gravitons would be allowed to leave the surface and move into the AdS5 bulk.In this work, we investigate gravitational waves as metric perturbations around a general warped 5-dimensional background. We find an analytical solution in Randall-Sundrum braneworld model andanalyze the implications of braneworld models in the gravitational waves propagation.

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6.6 Antonio Carlos Faria and Claudio Nassif: Relations between the speed of light,the temperature and the expansion of the Universe

From an extended relativistic dynamics for a particle moving in a cosmic background field with temper-ature T, we aim to obtain the speed of light with an explicit dependence on the background temperatureof the universe. Although founding the speed of light in the early universe much larger than its currentvalue, our approach does not violate the postulate of special relativity. Moreover, it is shown that thehigh value of the speed of light in the early universe was drastically decreased before the beginning of theinflationary period. So we are led to conclude that the theory of varying speed of light should be ques-tioned as a possible solution of the horizon problem. The advent of varying speed of light (VSL) theoriesseems to shake the foundations of special relativity theory, because the speed of light c in vacuum is nolonger constant. However, we must take care to investigate the veracity of such proposals. For this, wewill take into account an extended relativistic dynamics due to the presence of an isotropic backgroundfield with temperature T, where we consider that the energy scale at which a particle is subjected hasa nonlocal origin, representing the background thermal energy of the whole universe; i.e., the particleshould be coupled to the background field with temperature T, which leads to a correction on its energy.

6.7 Benedikt Herwerth: Optical Conductivity of Helical Superconductors

Optical conductivity and the superfluid density encode interesting features of holographic superconduc-tors and are crucial for the understanding of universal behavior such as Homes’ law. We study holographics-wave superconductors with explicitly broken translational symmetry due to a helical lattice structure.We find a second order phase transition at finite temperature with a scalar condensate. A linear responseanalysis reveals an expected Drude-like behavior of the optical conductivity in the normal phase. Ad-ditionally, the superconducting phase shows a characteristic infinite DC conductivity. Based on work inprogress with Johanna Erdmenger, Steffen Klug, Rene Meyer and Koenraad Schalm.

6.8 Stefan Janiszewski: Non-relativistic holography

Many non-relativistic Quantum Field Theories with conserved particle number share a common set ofsymmetries: time dependent spatial diffeomorphisms acting on the background metric and U(1) invarianceacting on the background fields which couple to particle number. Here we use these symmetries to deducea gravity dual for any such theory in terms of Horava gravity, a non-relativistic theory of gravity. Thisduality allows the extension of holography to generic non-relativistic field theories. As Horava gravityis presumed to be a consistent quantum theory, this duality also allows holography to move beyond thelimit of a large number of colors, in principle.

6.9 Yegor Korovin: Lifshitz as a deformation of AdS

We consider holography for Lifshitz spacetimes with dynamical exponent z = 1 + ε2, where ε is small.The holographically dual field theory is a specific deformation of the relativistic CFT, correspondingto the z = 1 theory. We set up the holographic dictionary for Einstein-Proca models and explain howrenormalization turns the relativistic conformal invariance into non-relativistic Lifshitz invariance withdynamical exponent z = 1 + ε2. Using only QFT arguments, it is possible to show that a particular classof deformations of CFTs generically leads to Lifshitz scaling invariance and we provide examples of suchdeformations. An analytic asymptotically Lifshitz black brane up to second order in ε is constructed.Based on 1304.7776

6.10 Victoria Martin: Entanglement Renyi Entropy via Uniformization of RiemannSurfaces

The Renyi entropies and entanglement entropy of 1+1 dimensional CFTs with gravity duals can becomputed by explicit construction of the bulk spacetimes dual to branched covers of the boundary ge-ometry. At the classical level in the bulk this has recently been shown to reproduce the conjecturedRyu-Takayanagi formula for the holographic entanglement entropy. We obtain the one-loop bulk cor-rections to this formula in several cases. The functional determinants in the bulk geometries are givenby a sum over certain words of generators of the Schottky group of the branched cover. For the case of

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two disjoint intervals on a line we obtain analytic answers for the one-loop entanglement entropy in anexpansion in small cross-ratio. These reproduce and go beyond anticipated universal terms that are notvisible classically in the bulk. We also study the case of a single interval on a circle at finite temperatureand find similar results.

6.11 Jiri Minar: Fermi-Hubbard Hamiltonian with non unitary tunnelings:Quantum simulator of general curved spacetimes with cold atoms

Quantum gases have proven to be a useful experimental tool to probe many particle physics at quantumlevel with an active effort towards a realization of quantum simulators of gauge theories. For backgroundnon abelian gauge fields, the physics on a lattice is typically described by a Hubbard type Hamiltonianwith unitary trunnelings. Possible non unitarity of these tunnelings represents qualitatively distinct andnew feature of the Hubbard type Hamiltonians. In this letter we provide a physical interpretation of suchtunnelings for fermionic particles. We show that a tight binding Fermi-Hubbard model with non unitarytunnelings can be mapped to Dirac Hamiltonian in a curved background spacetime. We find the form ofthe nonunitary tunneling matrices in terms of the metric tensor. This interpretation holds for a generalmetric tensor, in particular a time dependent one. We discuss how to synthesize such Hamiltonians bymeans of laser assisted tunnelings in cold atomic experiments and comment on the form of interactingfield theories which could be possibly simulated.

6.12 Claudio Nassif and Antonio Carlos Faria: Gravity from a universal lowerspeed regime in nature

The present work aims to find a consistent coupling between electromagnetic and gravitational fields,using an electron that couples to a gravitational potential by means of its electromagnetic field. To dothat, first of all, we build a heuristic model providing the electromagnetic origin of both the mass andthe energy of the electron, aiding with the idea of the photon-gamma decaying in a electron-positronpair. After this, we place the electron (or positron) in the presence of a gravitational potential so thatits electromagnetic field undergoes a very small perturbation, leading to a slight increase in the field’selectromagnetic energy density. This perturbation takes place by means of a tiny coupling constantsince gravity is an extremely weak interaction. We compute such coupling constant given in terms offundamental constants like gravity constant, electron mass constant, electron charge constant, Planckconstant and speed of light, and then we realize that it is a new dimensionless universal constant, whichreminds us the fine structure constant. However it is much smaller than the fine structure constant, sinceit includes gravity. We find a value to this coupling constant. This analysis can bring several implicationsfor the understanding of gravity in the relations between gauge theories duality.

6.13 Alexander Patrushev: Squashed cones and surface contributions toentanglement entropy.

We generalize the regularization procedure for the analysis of the Riemann geometry of manifolds withconical singularities for the case of squashed cones. In this case there is no rotational O(2) symmetry inthe subspace orthogonal to the singular surface. Contrary to the usual cones, when such a symmetry ispresent, the distributional nature of the conical singularities starts to depend essentially on the extrinsicgeometry of the singular surface. There exist only two possible combinations quadratic in the extrinsiccurvature. In order to fix the corresponding coefficients we work in flat spacetime and compute thequadratic curvature invariants in two special cases: when the singular surface is cylinder and when it isa sphere. Our results then allow to determine the contribution of extrinsic curvature for integral of anyquadratic combination of the Riemann curvature. In particular, for the Euler number and the square ofthe Weyl tensor we get the results which are in complete agreement with an earlier (partially based onholography) analysis of entanglement entropy of a 4d CFT. We generalize this result for the entropy ofany, not necessarily conformal, field theory in four dimensions. We make remarks on possible extensionsof our result to higher dimensions.

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6.14 Flavio Porri: Holographic R-symmetric flows and the τU conjecture

I will present recent results appeared on arXiv:1304.1481. I will discuss the holographic counterpart of arecent conjecture regarding R-symmetric RG-flows in four-dimensional supersymmetric field theories. Insuch theories, a quantity τU can be defined at the fixed points which was conjectured in arXiv:1109.3279to be larger in the UV than in the IR, τUV

U > τ IRU . I will analyze this conjecture from a dual supergravityperspective: using some general properties of domain-wall solutions dual to R-symmetric RG flows, I willdefine a bulk quantity which interpolates between the correct τU at the UV and IR fixed points. Studyingits monotonicity properties in a class of examples: a monotonic behavior is found for theories flowing toan interacting IR fixed point; for gapped theories, the monotonicity is still valid up to a finite value ofthe radial coordinate where the function vanishes, reflecting the gap scale of the field theory.

6.15 Andreas Samberg: Heavy Probes in Strongly Coupled Plasmas WithChemical Potential

We study the properties of heavy probes moving in strongly coupled plasmas at finite chemical potential.Using the gauge/gravity duality we consider large classes of gravity models. We report on our analysisof the screening distance of a quark-antiquark pair, its free energy, and the running coupling. Theseobservables show some insensitivity as to which model and deformation is used, pointing to strong-coupling universal behavior. Thus, the results may be relevant for modeling heavy quarkonia traversinga quark-gluon plasma at finite net baryon density, and their suppression by melting.

6.16 Jared Stang: Striped order in AdS/CFT

We study the formation of inhomogeneous order in the Einstein-Maxwell-axion system, dual to a 2+1dimensional field theory that exhibits a spontaneously generated current density, momentum densityand modulated scalar operator. Below the critical temperature, the Reissner-Nordstrom-AdS black holebecomes unstable and stripes form in the bulk and on the boundary. The bulk geometry possessesstriking geometrical features, including a modulated horizon that tends to pinch off as T → 0. Ona domain of fixed length, we find a second order phase transition to the striped solution in each of thegrand canonical, canonical and microcanonical ensembles, with modulated charges that grow and saturateas we lower the temperature and descend into the inhomogeneous phase. For the black hole on an infinitedomain, a similar second order transition occurs, and the width of the dominant stripe increases in thezero temperature limit.

6.17 Stephan Steinfurt: A universal fermionic analogue of the shear viscosity

We holographically compute supercharge diffusion constants in supersymmetric field theories, dual to AdSblack brane solutions of arbitrary dimension. This includes the extension of earlier work by Kontoudiand Policastro for D3-branes to M2- and M5-brane theories. We consider the case of vanishing chemicalpotential. In particular, we relate the product of a diffusion constant and the energy density to auniversal result for the fermionic absorption cross section. This relation is analogous to the famous proofof universality of η/s. We calculate the diffusion constants in two different ways: First, the computationis performed via the low frequency, low momentum pole of the correlator of supersymmetry currents.This pole describes the hydrodynamic phonino mode, the massless Goldstone fermion of spontaneoussupersymmetry breaking by temperature. Second, the calculation is carried out using the dual transversalmode of the bulk gravitino, with the help of a new Kubo formula. Moreover, we provide some evidencefor the applicability of generalized dimensional reduction for fermions when computing the correspondingDp-brane diffusion constants. Reference: arXiv:1302.1869

6.18 Migael Strydom: Spontaneous lattice ground states from a magnetic field

Making use of Gauge/Gravity Duality, we study two strongly coupled field theories that are the holo-graphic duals of SU(2) Einstein-Yang-Mills gravitational theories on asymptotically Anti-de Sitter back-grounds. One gravity setup is dual to a finite temperature field theory, while the other has a hard wallcutoff and is dual to a confining gauge theory. Both of these models undergo a superconducting phasetransition at large enough values of the magnetic field. This yields a condensate in the field theory that

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has a ground state resembling Abrikosov vortices of a type II superconductor to linear order in perturba-tion theory. These models are related to p-wave superconductors where the condensate is induced by afinite isospin density. The results presented here may be of relevance to both condensed matter physicsand heavy ion collisions. We also present a possible extension to the models.

6.19 Wilke van der Schee: From full stopping to transparency in a holographicmodel of heavy ion collisions

Numerically simulating colliding planar gravitational shock waves in AdS gives rise to rich and interestingdynamics. Wide shocks come to a full stop and expand hydrodynamically, as was found in [1]. Highenergy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms inthe middle, quite akin to heavy-ion collisions at LHC. Interestingly, we find a region of negative energydensity trailing behind the onmoving shocks. Also, the longitudinal pressure over the energy density atearly times is as low as -3, as predicted by analytic work using delta shocks [2]. After this initial stagethe pressures become positive and are governed by hydrodynamics within a time 1/T, with T the localtemperature at that time.

[1] P.M. Chesler, L.G. Yaffe, PRL 106 (2011)[2] D. Grumiller, P. Romatschke, JHEP 08 (2008)[3] J. Casalderrey-Solana, M.P. Heller, D. Mateos, W. van der Schee, 1305.4919

6.20 Jackson Wu: A Holographic Model of the Kondo Effect

We propose a new model of the Kondo effect, employing the AdS/CFT correspondence. The Kondo effectis the screening of a magnetic impurity coupled anti-ferromagnetically to a bath of conduction electronsat low temperatures. Our holographic model combines both the CFT and the large-N descriptions of theKondo effect, and it exhibits several characteristic features of the Kondo effect, including a dynamicallygenerated scale, and a spectral flow producing a phase shift. Our holographic Kondo model may be usefulfor studying many open problems involving impurities, including for example the Kondo lattice problem.

6.21 Hansjorg Zeller: Transport Properties of Holographic P-Wave Superfluids

We study transport phenomena in p-wave superfluids in the context of gauge/gravity duality. Due tothe spacetime anisotropy of this system, the tensorial structure of the transport coefficients is non-trivialin contrast to the isotropic case. In particular, there is an additional shear mode which leads to a non-universal value of the shear viscosity even in an Einstein gravity setup. On this poster, we present astudy of some of the helicity two, helicity one and helicity zero fluctuation modes. In addition to thenon-universal shear viscosity, we present the different behaviours of the ”electric” conductivities in thedirections transverse and parallel to the condensate. Moreover, we show a transport coefficient associatedto the normal stress difference which is not present in the isotropic case. In addition we present additionaleffects due to the anisotropy, e.g. the flexoelectric effect and the piezoelectric effect. These effects arewell-known in condensed matter physics. Finally, we analyse some of the results analytically close to thecritical temperature.

7 Acknowledgments

The conference is funded by the European Science Foundation through the HoloGrav Network.

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