Iberian Strings 2013
IST, Lisbon, January 22-25 2013


Review lectures (55 + 5 = 60 minutes)

Frederik Denef, Quantum cosmology, holography and complex systems

Bernard de Wit, Subleading corrections to BPS black hole entropy: N=2 supersymmetric higher-derivative couplings  and the 5D-4D connection

Subleading corrections to black hole entropy are induced by higher-derivative couplings. For BPS black holes many of these couplings will not contribute due to certain renormalization theorems. We review various approaches and recent results.

Óscar Dias, Fluid/gravity correspondence

First, I revisit old tantalising similarities between black hole physics, and the properties of soap bubbles and fluid lumps. Then I discuss the precise formal maps between gravity and hydrodynamics that were established in recent years. Finally, I describe how gravity studies can provide an opportunity to gain insights on turbulence.
This will be a colloquium-style LARSyS lecture targeting an audience that includes engineers, mathematicians, and physicists. Aspects and applications of this correspondence will be further covered in the lectures of Casalderrey, Heller and Obers.

Michal P. Heller, AdS/CFT out of equilibrium

The talk will review motivation, basic ideas and recent developments in describing holographically non-equilibrium phenomena in strongly coupled quantum field theories.

Veronika Hubeny, Holographic Entanglement Entropy \(\& \) Causal Holographic Information

Entanglement entropy is an important quantity characterizing quantum systems, employed in diverse areas of research ranging from condensed matter physics to quantum computing.  Using holography, an invaluable tool for elucidating certain strongly coupled quantum field theories by using their higher-dimensional classical gravitational dual, entanglement entropy is conjectured to be related to a simple geometrical construct: an area of an extremal surface in asymptotically AdS spacetime.  
In the first part of the talk, I will review this proposal and discuss some of the recent applications in time-dependent settings.  Motivated by the power of holography, in the second part of the talk I will introduce another (more basic) geometrical construct, whose dual is hitherto unknown but provisionally called "causal holographic information".  To understand its nature, I will contrast its predicted behaviour with that of the entanglement entropy and discuss its general properties.

Marcos Mariño, Matrix models for superstrings and M-theory

Localization methods express the partition functions of Chern-Simons-matter theories in terms of matrix models. By the AdS/CFT correspondence, they correspond to superstring and M-theory partition functions in certain AdS backgrounds. In this talk I will provide an overview of the results that have been recently obtained in this area. First I will summarize the different methods that have been developed to study the matrix models at large N, and then I will discuss the implications for M-theory and superstrings. A well-known result of this approach is the derivation of the 3/2 scaling in the number of degrees of freedom for a theory of M2-branes, but this is just the tip of the iceberg: the matrix model encodes information about subleading corrections in the 1/N expansion, which can be tested against quantum supergravity. It also makes it possible to calculate non-perturbative membrane effects in M-theory.

Miguel Paulos, Bootstrapping CFTs with the Extremal Functional Method

The existence of a positive linear functional acting on the space of (differences between) conformal blocks has been shown to rule out regions in the parameter space of conformal field theories (CFTs). We argue that at the boundary of the allowed region the extremal functional contains, in principle, enough information to determine the dimensions and OPE coefficients of an infinite number of operators appearing in the correlator under analysis. Based on this idea we develop the Extremal Functional Method (EFM), a numerical procedure for deriving the spectrum and OPE coefficients of CFTs lying on the boundary (of solution space). We test the EFM by using it to rederive the low lying spectrum and OPE coefficients of the 2d Ising model based solely on the dimension of a single scalar quasi-primary -- no Virasoro algebra required. Our work serves as a benchmark for applications to more interesting, less known CFTs in the near future, such as the 3d Ising model.

Sakura Schäfer-Nameki, F-theory and Supersymmetric GUTs

F-theory has emerged in recent years as an ideal framework to realize supersymmetric Grand Unified Theories in string theory. I will first review the basic local model building paradigm in F-theory. In the second part I will explain recent developments in global realizations of these, including the construction of the geometries and fluxes.


Short talks (25 + 5 = 30 minutes)

Carlos Shahbazi Alonso, Non-extremal quantum black holes in type IIA string theory

We study black hole solutions of Type-IIA Calabi-Yau compactifications in the presence of perturbative quantum corrections. We define a class of black holes that only exist in the presence of quantum corrections and that, consequently, can be considered as purely quantum black holes. The regularity conditions of the solutions impose the topological constraint \(h^{1,1}>h^{2,1}\) on the Calabi-Yau manifold, defining a class of admissible compactifications, which we prove to be non-empty for \(h^{1,1}=3\) by explicitly constructing the corresponding Calabi-Yau manifolds, new in the literature.

Inês Aniceto, The resurgence of instantons in string theory

In order to study the weakly coupled regime of theory we often make use of perturbative expansion of the physical quantities of interest. But such expansions are often divergent and defined only as asymptotic series. In fact, this divergence is connected to the existence of nonperturbative contributions, i.e. instanton effects that cannot be captured by a perturbative analysis. The theory of resurgence is a mathematical tool which allows us to effectively study this connection and its consequences. In this talk we will make use of this theory in order to show how to construct a full nonperturbative solution from pertubative data. To write this full nonperturbative solution we need to introduce generalised multi-instanton sectors, which can then be checked by precision tests on the asymptotic data. Finally, the study of this nonperturbative sectors in matrix models allows us to have a full picture of the phase diagram of this models.

Igor Bandos, Action for the eleven-dimensional multiple M-wave system

We present the covariant supersymmetric and kappa-symmetric action for a system of \(N\) nearly coincident M-waves (multiple M0-brane system) in flat eleven dimensional superspace.

Pablo Bueno, Lifshitz-like solutions with hyperscaling violation in gauged supergravity and string theory

We investigate the existence of Lifshitz-like metrics with hyperscaling violation in the context of \(N = 2, d = 4\) Supergravity with Fayet-Iliopoulos terms. After establishing some general results on the properties of purely hvLf solutions in these theories, we show how consistent truncations of two particular models (\(t^3\) and axion-dilaton), some of which can be embedded in String Theory, admit electric, magnetic and dyonic black hole solutions with this behavior.

Jorge Casalderrey-Solana, Off-diagonal flavour susceptibilities from AdS/CFT

We study flavour susceptibilities in the \(N=4\) \(SU(N)\) super Yang-Mills plasma coupled to two quark flavours at strong coupling and large \(N\) by means of its gravity dual. The off-diagonal susceptibility is \(1/N\)-suppressed and we compute it as a one-loop effect on the gravity side. Contrary to naive extrapolation from perturbative results, it attains a finite value in the infinite-coupling limit. Moreover, its parametric form is independent of whether or not meson bound states exist in the plasma. We conclude that caution must be exercised when drawing conclusions about the QCD plasma from lattice calculations of quark susceptibilities.

Martin Cederwall, Exceptional generalised geometry

I review the construction of gauge transformations, connections, curvatures etc. in generalised geometry, with focus on the exceptional setting, adapted to U-duality. The matter content of maximally supersymmetric generalised supergravity is sketched in terms of sequences of modules naturally generalising forms. Some interesting problems are pointed out and discussed.

Eoin Colgain, \(F(4)\) supergravity and non-abelian T-duality

Recently it was realised that non-Abelian T-duality can be applied to the only known supersymmetric AdS6 solution to generate a new supersymmetric AdS6 solution. Since this solution corresponds to the supersymmetric vacuum of Romans' \(F(4)\) supergravity, we ask if one can identify a new embedding of all of \(F(4)\) in type II supergravity.

Marko Djuric, Vector meson production from AdS/CFT

We use gauge/gravity duality to study the production of \(\rho\), \(\omega\), \(J/\Psi\) and \(\phi\) mesons, in the limit of high center of mass energy at fixed momentum transfer, corresponding to the limit of low Bjorken \(x\), where the process is dominated by the exchange of the pomeron. This is an extension of our previous work on deep inelastic scattering and deeply virtual Compton scattering. We compare our AdS/CFT calculations to experimental data from HERA experiments, both for differential and exclusive cross sections.

Pietro Galli, Freudenthal duality in four-dimensional black holes

We show and discuss the existence and consequences of a local invariance in the HFGK description of black-hole solutions of 4-dimensional supergravity theories. Some of the results have been presented in arXiv:1211.7296

Vasco Gonçalves, Conformal Regge theory

We generalize Regge theory to correlation functions in conformal field theories. This is done by exploring the analogy between Mellin amplitudes in AdS/CFT and S-matrix elements. In the process, we develop the conformal partial wave expansion in Mellin space, elucidating the analytic structure of the partial amplitudes. We apply the new formalism to the case of four point correlation functions between protected scalar operators in \(N=4\) Super Yang Mills, in cases where the Regge limit is controlled by the leading twist operators associated to the pomeron-graviton Regge trajectory. At weak coupling, we are able to predict to arbitrary high order in the 't Hooft coupling the behaviour near \(J=1\) of the OPE coefficients \(C_{OOJ}\) between the external scalars and the spin \(J\) leading twist operators. At strong coupling, we use recent results for the anomalous dimension of the leading twist operators to improve current knowledge of the AdS graviton Regge trajectory - in particular, determining the next and next to next leading order corrections to the intercept. Finally, by taking the flat space limit and considering the Virasoro-Shapiro S-matrix element, we compute the strong coupling limit of the OPE coefficient \(C_{LLJ}\) between two Lagrangians and the leading twist operators of spin \(J\).

Sebastian Guttenberg, The quantum Siegel algebra

The Siegel Algebra is the classical gauge algebra of the Green Schwarz superstring. It is generated by Virasoro constraints and kappa-symmetry and is lacking an anomaly free quantum version since 1985. I will present a quantum algebra within the pure spinor formalism that reduces at classical level to Siegel's algebra and shows strong evidence to be anomaly free. It reveals additional interesting structure that has not been manifest in the classical algebra. At the same time it gives new important insight to the CFT of the pure spinor string.

Amadeo Jimenez, Anomalous conductivities from rotating ensembles

Chiral Anomalies give rise to new and non-dissipative transport phenomena. These are the chiral magnetic and the chiral vortical effects. The chiral vortical effect has been shown to receive a contribution stemming from the mixed gauge gravitational anomaly. We compute generalizations of this effect for chiral fermions in arbitrary (even) dimensions using a thermal ensemble with fixed angular velocities.

Niko Jokela, Brane models of \(2+1\) dimensional fermions

I will discuss two holographic probe brane models of strongly-coupled fermions in \(2+1\) dimensions, the D3-D7' and D2-D8' systems.  In addition to realizing a gapless holographic quantum liquid, of the type found in related brane models, these systems also contain novel gapped quantum Hall states.  While the quantum Hall states are stable, the gapless states are subject to spatially modulated instabilities.

Stefanos Katmadas, Ungauging black holes and hidden supercharges

After a short introduction to the structure of the general solution for under-rotating black holes in four dimensional ungauged supergravity, the close similarity to the 1/4-BPS black holes in abelian gauged supergravity will be established. Analysing the corresponding squaring of the action, we show that all asymptotically flat solutions can be embedded in the gauged theory, in exactly the same way as the 1/4-BPS solutions in AdS, up to a Lagrange multiplier imposing the vanishing of the potential. We point out that at the attractor, the multiplier reduces to unity, so that there is a unique class of N=1 attractors describing both kinds of asymptotics. Finally, some interesting observations on the possibility of adding hypers and on the structure of black hole solutions in AdS will be highlighted.

Liuba Mazzanti, Probes in holographic plasmas with unquenched quarks

We analyze the holographic gravity model dual to a quark-gluon plasma with massless dynamical quarks in the Veneziano limit. The background of smeared D7 branes in a D3 near horizon geometry is reviewed. On top of this we add probe D7 branes to produce results for phenomenologically relevant quantities such as the meson melting phase transition point, the screening length, the drag force and diffusion constants for a heavy quark.

Luis Melgar, Holographic type II Goldstone modes

We study a holographic model dual to a CFT in \(2+1\) dimensions at finite temperature and chemical potential with a gobal \(U(2)\) symmetry. At large enough chemical potential spontaneous symmetry breaking occurs and breaks the symmetry to \(U(1)\). The non-abelian nature of the symmetry and the explicit Lorentz breaking by the chemical potential imply the presence of an ungapped mode with quadratic dispersion relation in the broken phase. Such modes are called Type II Goldstone bosons and have several distinguished features that we study within the framework of this holographic model.

Niels Obers, (Electro)elasticity from gravity

I will discuss new aspects of (charged) black branes, recently discovered within the blackfold approach. In particular, by considering the extrinsic dynamics of black branes it is established that these can be viewed as materials, characterized by new response coefficients such as Young modulus and piezoelectric moduli.  This linkage parallels the hydrodynamic behavior of black branes found in recent years, which has its origin in the intrinsic dynamics of black branes.

Alvaro Osorio, On the sigma-model of deformed special geometry

We discuss the deformed sigma-model that arises when considering four-dimensional \(N=2\) abelian vector multiplets in the presence of an arbitrary chiral background field. In addition, we allow for a class of deformations of special geometry by non-holomorphic terms. We analyze the geometry of the sigma-model in terms of intrinsic torsion classes. We also express the deformed sigma-model in terms of the Hesse potential that underlies the real formulation of special geometry.

Jan Perz, Systematic construction of black hole solutions in \(N=2\) supergravity

Using an extension of Denef's formalism or the H-FGK approach, the effective action for black holes in four- and five-dimensional \(N=2\) supergravity coupled to vector multiplets can be rewritten in terms of suitably chosen variables (functions of the warp factor and the physical scalars) that have the same duality transformation properties as the electric and magnetic charges. Apart from simplifying the equations of motion, this makes the solutions for a given model take the same universal form, independently of supersymmetry or extremality, allowing both extremal and non-extremal black holes to be constructed systematically, including in particular analytic solutions in a supergravity model with a quantum correction to the prepotential.

Alessandro Sfondrini, Integrability for the \(AdS_3/CFT_2\) correspondence

An interesting instance of the AdS/CFT correspondence is the case of \(AdS_3/CFT_2\). Strings on \(AdS_3 \times S^3 \times S^3 \times S^1\) can be completely understood when the background is purely NSNS thanks to 2-dimensional conformal symmetry. Unfortunately this symmetry is not as useful in the case of RR backgrounds. However, it appears that the integrability techniques that proved successful in understanding the planar limit of \(AdS_5/CFT_4\) may be applicable also here, which sparked new interest and efforts in this field. I will review such techniques and report on the recent developments in the understanding of the string spectrum on \(AdS_3 \times S^3 \times S^3 \times S^1\).

Wilke van der Schee, Holographic thermalisation with radial flow

In this short talk I will discuss the thermalisation of far-from-equilibrium states in a strongly coupled gauge theory, using holography. One way to study this is to solve Einstein equations numerically, the famous example being the colliding shock waves of Chesler and Yaffe. Recently, I extended this analysis by considering an evolution with radial flow and I will try to give clear insights how to tackle such problems technically.

Dimitrios Zoakos, Thermodynamics of the brane in Chern-Simons matter theories with flavor

We study the holographic dual of flavors in a Chern-Simons matter theory at finite temperature, realized as a D6-brane probe in the type IIA black hole dual to the ABJM theory. We consider both massive and massless flavors. The former are treated in the quenched approximation, whereas the massless ones are considered as dynamical objects and its backreaction on the geometry is included in the black hole background. We compute several thermodynamical functions for the system and we analyze the meson melting phase transition between Minkowski and black hole embeddings.