Program

9:00

Registration

9:20

Opening

Arefeva

9:30-10:45

Landsteiner

Gelis

Yaffe

Casalderrey

11:15-12:30

Mateos

Costa

Rebhan

Jokela

12:30-13:15

Murata

Kaminski

Kumar

Evans

15:30-16:15

Hoyos

Heller

Bigazzi

Buchel

16:15-17:00

Tarrio

Armesto

Jankowski

Baggioli

17:30-18:00

Ecker

Mukhopadhyay

Schee

Spalinski

18:00-18:30

Meiring

Jarvinen

Ishii

Ballon

18:30-19:00

Quevedo

19:30

Welcome Wine

20:30

Banquet

Name

Abstract

Arfeva, Irina

Non-zero chemical effects in holographic renorm-group flow. The holographic RG flow with non-zero chemical potential will be discussed in isotropic and anisotropic cases.

Armesto, Nestor

Initial stages in heavy-ion collisions: from small to large systems. I will review our current understanding of the initial stages in high-energy heavy-ion collisions. I will discuss the physics that may lead to the appearance of azimuthal asymmetries, and the eventual relation of the findings in small collision systems with that in large ones. The focus will be on weak coupling explanation and how they confront the success of the relativistic hydrodynamics description.

Baggioli, Matteo

Quantum Criticality gives me butterflies. We study two different aspects of the holographic Weyl semimetal quantum phase transition (QPT). (I) We analyze the effects of quenched disorder and we observe the smearing of the QPT, the rare regions effects and the appearance of discrete scale invariance. (II) We probe the onset of quantum chaos, and in particular the behaviour of the butterfly velocity in the quantum critical region. We discuss the effects of anisotropy and we propose a universal bound which is implied by the bulk Null Energy Condition (NEC).

Ballon Bayona, Alfonso

An order parameter for Inverse Magnetic Catalysis. In this talk I will describe the phenomenon of Inverse Magnetic Catalysis (IMC) at finite quark density using a holographic model for Quantum Chromodynamics (QCD), known as the Sakai-Sugimoto model. After briefly reviewing the state of the art of IMC, at zero and finite quark density, I will focus on the finite density case where I will show explicitly how the magnetisation acts as an order parameter to distinguish IMC from the traditional Magnetic Catalysis (MC).

Bigazzi, Francesco

Top-down holography and the Chern-Simons Diffusion Rate. We will show that, within a large class of planar strongly correlated gauge theories with dual string description, the Chern-Simons diffusion rate is simply given in terms of temperature, entropy density and gauge coupling, with a universal numerical coefficient. This result holds, in fact, for all the top-down holographic models where the calculation has been performed in the past, even in presence of magnetic fields and anisotropy. Finally we point out some subtleties related to the definition of the Chern-Simons diffusion rate in the presence of anomalies. The holographic computation of the rate - as a late time limit of the imaginary part of the retarded correlator of the topological charge density - gives an exactly vanishing result in this case. Nevertheless, a non-trivial Chern-Simons relaxation time can be safely defined.

Buchel, Alex

Holographic hydrodynamics of gauge theory plasma. Beyond large-N and beyond Navier-Stokes. We study hydrodynamics of four-dimensional non-conformal holographic plasma with non-equal central charges at the ultraviolet fixed point. We compute equation of state, the speed of sound waves, transport coefficients (shear and bulk viscosities), and discuss causality. We study the asymptotic character of the hydrodynamic series for the homogeneous and isotropic expansion of the plasma.

Carcassés Quevedo, Robert

Non-minimal coupling contribution to DIS at low x in Holographic QCD.
We consider the effect of including a non-minimal coupling between a U(1) vector gauge field and the graviton Regge trajectory in holographic QCD models. This coupling describes the QCD interaction between the quark bilinear electromagnetic current and the Pomeron. We test this new coupling against DIS data at low Bjorken x and obtain an excellent fit with a chi squared of 1.1 over a very large kinematical range in the photon virtuality Q2<400 GeV2 and for x<10−2. The scale of the new dimension full coupling, which arises from integrating higher spin fields, is of order 1-10 GeV. This value matches precisely the expectations from effective field theory, which indicate that such corrections are controlled by the mass gap between the spin two and spin four glueballs that are described holographically by the graviton and spin four field in the graviton Regge trajectory, respectively.

Casalderrey-Solana Jorge

Holographic approaches to the study of strongly interacting matter in extreme conditions

Costa, Miguel

The holographic Pomeron and low-x physics. Regge theory has a long history in particle physics, particularly in QCD and String Theory. In the case of QCD, the forward limit of elastic processes is dominated by the exchange of a Reggeon, known as the Pomeron. In such processes the partonic structure of hadrons is largely dominated by a dense gluon medium, which undermines perturbative QCD techniques. In the gauge/string duality the Pomeron is mapped into the graviton Regge trajectory. In this talk we use the framework of Regge theory for conformal field theories and then for strings in asymptotically AdS spaces to develop a dual phenomenological approach for Pomeron physics. We exemplify with the case of deep inelastic scattering at low-x and reproduce experimental data over a vast kinematical range including regions where perturbative QCD techniques break down.

Ecker, Christian

Dynamics from Semi-Holography. In this talk I will introduce the semi-holographic approach to heavy ion collisions originally proposed by E. Iancu and A. Mukhopadhyay in (1410.6448) and further developed in (1512.06445). The semi-holographic approach makes it possible to self-consistently evolve a system of weakly coupled glasma fields interacting with a strongly coupled sector described by holography. I will discuss recent progress in computing numerical solutions within this framework and show first results featuring energy transfer from the weakly coupled to the strongly coupled sector during the time evolution.

Evans, Nick

A Holographic Description of Colour Superconductivity. The difficulty of describing the gauge dependent bi-quark condensate in the QCD colour superconducting phase has made it hard to construct a holographic dual of the state. To side step this problem, we argue that near the chiral restoration transition in the temperature-chemical potential plane, the strongly coupled gluons are likely completely gapped so that the colour quantum numbers of the quarks can be thought of below that gap as global indices. A standard AdS-superconductor model can then be used to analyze the fermionic gap formation. We investigate the role of four-fermion interactions, which might be used to include the gapped QCD interactions, on the vacuum and metastable vacua of the model. It turns out to be easiest to simply relate the standard interaction of the holographic superconductor to the strength of the gapped gluons. The result is a holographic description of the QCD colour superconducting phase diagram. We take a first look at how quark mass enters and causes a transition between the colour flavour locked phase and the 2SC phase.

Gelis, Francois

Isotropization in the Color Glass Condensate. Many observables in heavy ion collisions are consistent with the expansion of a relativistic fluid with very small viscosity. In this talk, I will review some recent works aiming at understanding this behavior from the point of view of QCD.

Heller, Michal

How does relativistic kinetic theory remember about initial conditions? Understanding hydrodynamization in microscopic models of heavy-ion collisions has been an important topic in current research. Many lessons obtained within the strongly-coupled (holographic) models originate from the properties of transient excitations of equilibrium encapsulated by short-lived quasinormal modes of black holes. The aim of this paper is to develop similar intuition for expanding plasma systems described by, perhaps, the simplest model from the weakly-coupled domain, i.e. the Boltzmann equation in the relaxation time approximation. We show that in this kinetic theory setup there are infinitely many transient modes carrying at late times the vast majority of information about the initial distribution function. They all have the same exponential damping set by the relaxation time but are distinguished by different power-law suppressions and different frequencies of very slow, logarithmic in proper time, oscillations. Finally, we analyze the resurgent interplay between the hydrodynamics and transients. In particular, show that there are choices of relaxation time dependence on temperature for which the asymptotics of the divergent hydrodynamic series is dominated not be the least damped transient, but rather by an unphysical exponential correction having to do with non-analyticities of the equation of motion in complexified time variable. Based on 1609.04803, 1802.08225.

Hoyos, Carlos

A defect action for Wilson loops. An effective defect action is proposed to compute the expectation value of Wilson loops in (S)U(N) gauge theories. For a circular Wilson loop it is found that the expectation value coincides at leading order with the exact result of the 1/2 BPS Wilson loop of N=4 super Yang-Mills. This hints towards a universal connection to string theory duals and SYK models.

Ishii, Takaaki

Floquet holographic superconductors. Interests in applying holography would include studying nonequilibrium states of strongly interacting systems. I will talk about applying a rotating electric field to a holographic model of superconductivity and constructing superconducting steady solutions. Thanks to the setup, a clear separation can be seen in the normal and superconducting components of the current induced by the electric field. Effects of the rotation on superconducting phase transitions are also discussed.

Jankowski, Jakub

Asymptotic behaviour of the late-time expansion of Yang-Mills plasma. We show that the late-time expansion of Bjorken flow in N=4 SYM theory encodes in an intricate way the spectrum of non-hydrodynamic modes. The AdS/CFT correspondence implies that this spectrum reflects the frequencies of AdS black-brane quasinormal modes. At the linearized level each quasinormal mode introduces a sector with a separate asymptotic gradient expansion. A mathematically consistent description of physical quantities such as the energy density can be obtained by recognizing that the emerging structure is a resurgent transseries. It is also
clear that one has to go beyond the linearized approximation and include sectors which can be thought of as involving nonlinear couplings between the different quasinormal modes. Using the AdS/CFT correspondence we have calculated the coefficients of the gradient series in the leading transseries sectors and verified the consistency of our transseries description using resurgence techniques.

Jarvinen, Matti

Inverse Magnetic Catalysis in Holographic. QCD Lattice simulations have shown recently that, contrary to earlier expectations, the chiral condensate is suppressed with growing magnetic field near the chiral and deconfinement transition temperatures of QCD, a phenomenon now known as “Inverse Magnetic Catalysis”. I demonstrate that inverse magnetic catalysis is found in bottom-up holographic models which include the backreaction of the flavors to the glue dynamics. The results compare well with lattice data for the condensate and related observables. In particular, the model predics the extent of inverse catalysis at finite chemical potential, where no lattice data is currently available.

Kaminski, Matthias

Correlations far from equilibrium in strong magnetic fields. A surprising agreement between lattice QCD data and N=4 Super-Yang-Mills theory (SYM) subjected to an external magnetic field arises for the ratio, R, of longitudinal to transverse pressure; where R is quantifying the anisotropy generated by the magnetic field. This motivates us to introduce an additional (initial) anisotropy into SYM, driving the system far away from equilibrium, using the holographic isotropization approach [Chesler, Yaffe (2008)]. We consider two-point functions of neutral and charged operators calculated in the geodesic approximation [Balasubramanian, Ross (2000)]. We compare to two-point functions near equilibrium, which encode the transport coefficients of SYM in a magnetic field at strong coupling.

Kumar, Prem

Entanglement of heavy quark impurities and holography. We discuss how the introduction of heavy quark probes into strongly coupled four dimensional gauge theories affects the quantum entanglement of a spatial region R containing the quark, with its complement. Of particular interest will be probes that are non-conformal, exhibiting flows on their world volumes and how their contribution to holographic entanglement/gravitational entropy varies with the size of the region R . We will discuss the results obtained from holography in light of the g-theorem and its putative generalisation to higher dimensions.

Landsteiner, Karl

Anomalous Transport from holography, in and out of equilibrium. I will review anomalous transport phenomena such as the chiral magnetic and the chiral vortical effect from the point of view of holography. I'll discuss the role played by (near) equilibrium physics and also present some results on anomalous transport in far from equilibrium situations where neither temperature nor chemical potential are well defined.

Mateos, David

Extreme Holography .
A massive experimental effort will be devoted in the coming years to the physics of QCD at high energy density and/or high baryon density. Understanding this physics, especially out of equilibrium, is an important theoretical challenge. I will discuss how holography can help us address this challenge. Topics covered will include the far-from-equilibrium dynamics near the QCD critical point and colour superconducting phases.

Meiring, Ben

Hydrodynamization and Attractors at Intermediate Coupling. The tremendous success of hydrodynamics in describing the Quark-Gluon Plasma poses many challenges to our understanding of collective phenomena in interacting systems out of equilibrium. Recently the concept of hydrodynamic attractors, which generalise the gradient expansion beyond local thermal equilibrium, has been put forward. In this talk, we will present the first analysis of this configuration at intermediate coupling. Using holography, we resum large orders in the gradient expansion to constrain the hydrodynamization dynamics and the attractor beyond the strong coupling limit. We find that independent of the coupling, hydrodynamization occurs at early times, when the pressure anisotropies are large and that the attractor is determined by first order hydrodynamics. By comparing our results to kinetic theory, we also observe that the approach of different configurations to the attractor is faster in gravity/based computation than in extrapolation of kinetic theory to intermediate coupling.

Mukhopadhyay, Ayan

Semi-holographic non-Fermi liquids. I will present a class of semi-holographic non-Fermi liquids which can be described by a generalisation of Landau's theory. In such non-Fermi liquids, Fermi liquid features are preserved in an inner core of the continuum while the Lindhard response function in other parts of the frequency and momentum domain is incoherent. A study of the dynamical in-medium screening points towards a novel pairing mechanism similar to the mid-infrared scenario proposed earlier by Leggett from a phenomenological point of view.

Murata, Keiju

Holographic Floquet states. With the aim to reveal universal features of hadronic matter and correlated Dirac insulators in strong AC-electric fields, we study the N=2 supersymmetric QCD with a finite quark mass driven by a rotating electric field. The analysis is done in the holographically dual D3/D7 system. The nonequilibrium phase diagram is determined from the threshold electric field at which the insulator phase breaks down to a conductive phase due to the AC version of the Schwinger mechanism. Intriguing features are observed as the frequency approaches resonance with the meson excitation energy. There, the threshold minimizes and a condensate of vector mesons with oscillating current exists even in the zero driving field limit. Our finding has many similarities with exciton BEC discussed in solid state systems, where the semiconductor is to be replaced by materials hosting gapped Dirac electrons.

Niko Jokela

Neutron stars in need of holography. Compressing cold matter past saturation density poses a major challenge for theorists. In this regime, the standard techniques e.g. perturbation theory or lattice studies are not applicable. This means that our understanding of the interior of neutron stars is crucially lacking. I will review holographic attempts for educated guesswork.

Rebhan, Anton

Semi-holographic approaches to quark-gluon plasma physics. Semi-holography attempts to combine weak and strong coupling physics such that the latter is described by gauge/gravity duality. I describe the recent progress made along these lines concerning thermalization as well as transport coefficients in a hybrid fluid model.

Spalinski, Michal

Universality and transient effects in N=4 SYM plasma. Numerical simulations of expanding plasma based on the AdS/CFT correspondence as well as kinetic theory and hydrodynamic models strongly suggest that some observables exhibit universal behaviour even when the system is not close to local equilibrium. This leading behaviour is expected to be corrected by transient, exponentially decaying contributions which carry information about the initial state. Focusing on late times, when the system is already in the hydrodynamic regime, we analyse numerical solutions describing expanding plasma of strongly coupled N=4 supersymmetric Yang-Mills theory and identify these transient effects. In the process we offer additional evidence supporting the recent identification of the Borel sum of the hydrodynamic gradient expansion with the far-from-equilibrium attractor in this system.

van der Schee, Wilke

Jet energy loss in a flowing plasma We present new results on the energy loss of light partons traversing a highly dynamical strongly coupled quark-gluon plasma. As QGP has large gradients in both temperature and the fluid velocity, it is crucial to study energy loss without assuming a homogeneous plasma, especially as it is known that energy loss depends on the virtuality of the partons, which evolves in the plasma. In a holographic description, we consider several subsequent improvements of the hydrodynamic background by keeping increasing orders in the gradient expansion. Varying temperature and velocity profiles in ideal hydrodynamics considerably modifies the energy loss, with further corrections from viscous effects. We then perform a numerical analysis of jet energy loss of an ensemble of jets in a boost-invariant and transversely-expanding droplet of QGP, for both small and large systems. Including flow increases the nuclear modification factor and reduces the narrowing of the jet shapes. We end with the modifications of the jet width and mass distributions, both for a flowing and non-flowing medium.

Tarrio, Javier

Holographic Quark Matter and Color Superconductivity. I will discuss a mechanism that describes the spontaneous breaking of the gauge (color) group in strongly coupled N=4SYM coupled to charged fundamental matter. The system is holographically described by an intersection of D3 and D7 branes, with a global (baryonic) U(1) charge on the worldvolume of the latter. Backreaction of the D7 branes and the baryonic charge on the geometry is crucial in this mechanism, since the IR geometry is responsible for the instability towards the breaking of the color group.

Yaffe, Larry

Long range phenomena in high density QCD. Interesting properties of high density QCD may be revealed by examining the holonomy effective potential which arises when one spatial dimension is compactified. Current understanding of the result, and its implications for vortex dynamics and quark/hadron continuity, will be discussed.