Past seminars

Andrea Zanetti

University of Milan

A Quantum Mechanics for Magnetic Horizons

In this Journal Club we are going to discuss the paper (2212.00672) "A Quantum Mechanics for Magnetic Horizons". This is the second part of the JC, where we are going to dive into the details of the construction of the Quantum Mechanical model. We are going to see how it's Witten index matches with the twisted index of the corresponding 3d theory.

Sara Pasquetti

Università degli Studi di Milano Bicocca

The local dualisation algorithm at work

I will present an algorithm to construct mirror and more general SL(2,Z) duals of 3d N=4 quiver theories and of their 4d uplifts. The algorithm uses a set of basic duality moves and the properties of the duality-walls providing a generalisation of the Kapustin-Strassler local dualisation to the non-abelian case. All the basic duality moves can be derived by iterative applications of Seiberg-like dualities, hence our algorithm implies that mirror and SL(2,Z) dualities can be derived assuming only Seiberg duality. I will also discuss the case of bad theories, where the dualisation algorithm allows us to extract non-trivial information on the quantum moduli space.

Davide Morgante

Università degli studi di Milano Statale

Non-invertible symmetries in holography

In this Journal Club we are going to talk about the paper (2210.09146) "The Holography of Non-Invertible Self-Duality Symmetries". The JC is going to be devided in two parts. The first will be a review of generalized and non-invertible symmetries (some basic concepts of category theory and fusion categories) with some basic examples, self-duality defects, condensation defects and the SymTFT approach. The second part will concern the discussion on actual paper.

Pedro Alvarez

Universidad de Antofagasta, Antofagasta, Chile

Conformal superalgebra GUT

We present a GUT model based on the conformal superalgebra. The model is based on an implementation of supersymmetry where matter fields are in the adjoint representation. We will discuss some of the details of the construction.

Marcello Ortaggio

Czech Academy of Sciences, Prague, Czech Republic

Universal Einstein-Maxwell solutions

Certain classes of Einstein spacetimes are known to be "immune" to higher-order corrections, i.e., they are simultaneous solutions of (virtually) any modification of Einstein's gravity in vacuum. In this talk we report on recent progress for the case of Einstein-Maxwell solutions, for which one has to consider also the backreaction of the electromagnetic field as well as corrections to the Maxwell equations. After giving a characterization of (at least some) universal Einstein-Maxwell solutions, we exemplify the obtained results in the case of particular theories such as ModMax or Horndeski electrodynamics.

Anastasios Petkou

Aristotle University, Thessaloniki, Greece

The Ubiquitous Conformal Symmetry

Conformal symmetry is a powerful tool in all our attempts to study physical systems by quantum field theory methods. In this talk I will review a few of its most well-known recent applications. Particular emphasis will be given to a mysterious recent observation that connects thermal one-point functions of massive theories in higher dimensions to multiloop massless Feynman integrals in four dimensions. This last example shows that conformal symmetry still has the ability to surprise us with its omnipresence.

Luca Ciambelli

Université Libre de Bruxelles, Bruxelles, Belgium

New Perspectives on (Quantum) Gravity

We expect certain universal results in classical gravity to come unaltered from a quantum theory of gravity. In this talk, I will firstly discuss new ideas on this topic, and the latest understanding we have on this, in an accessible way. After that, I will focus on local symmetries in gravity, and obtain the most general off-shell algebra of diffeomorphisms that acts non-trivially at corners, where gauge charges are supported. Noether charges in Einstein gravity are then shown to generate a faithful representation of this algebra. After pausing and reviewing the covariant phase space formulation, explaining the questions and issues our community faced in successfully applying it to gravity, I will show how a careful treatment of embeddings allows us to establish a field space where Noether charges act canonically via Poisson bracket. This solves a longstanding puzzle in this field, opening doors to new promising investigations. I will conclude by mentioning them and commenting on how new proposals might shed light on old unanswered questions in quantum gravity.

Matteo Broccoli

Max-Planck-Insitut für Gravitationsphysik (Albert-Einstein-Institut), Potsdam, Germany

The Third Way to Interacting p-form Theories

In three spacetime dimensions certain gravitational and gauge theories are ‘third way’ consistent. This means that their equations of motion are only on-shell consistent and do not come from the variation of an action which contains the dynamical field alone. Although this mechanism is not special to 3d, no higher dimensional third way consistent theory was known. In this talk, I will introduce the third way by presenting the 3d theories and show how we recover them by shifting a flat gauge connection. Applying the same method in higher dimensions, we find a new class of interacting (d-2)-form theories and I will discuss various generalisations of them. Our result proves that the third way can be realised in dimensions higher than three, and I will conclude by discussing the possibility of constructing new third way consistent theories of gravity.

Gaston Giribet

Universidad de Buenos Aires, Buenos Aires, Argentina

The infinite symmetries of magnetized horizons

We study stationary black holes in the presence of an external strong magnetic field. In the case where the gravitational backreaction of the magnetic field is taken into account, such a scenario is well described by the Ernst-Wild solution to Einstein-Maxwell field equations, representing a charged, stationary black hole immersed in a Melvin magnetic universe. This solution, however, describes a physical situation only in the region close to the black hole. This is due to the following two reasons: Firstly, Melvin spacetime is not asymptotically locally flat; secondly, the non-static Ernst-Wild solution is not even asymptotically Melvin due to the infinite extension of its ergoregion. All this might seem to be an obstruction to address a scenario like this; for instance, it seems to be an obstruction to compute conserved charges as this usually requires a clear notion of asymptotia. Here, we circumvent this obstruction by providing a method to compute the conserved charges of such a black hole by restricting the analysis to the near horizon region. We compute the Wald entropy, the mass, the electric charge, and the angular momentum of stationary black holes in highly magnetized environments from the horizon perspective, finding results in complete agreement with other formalisms.

Chiara Toldo

University of Amsterdam, Amsterdam, Netherlands

New horizons for holography

Motivated by gauge/gravity duality, there has been considerable interest in understanding the dynamics of asymptotically Anti-de Sitter (AdS) configurations such as black holes, especially the ones having an embedding in M-/string theory. In this talk I will review recent results regarding the construction and characterization of such solutions and I will explain their relevance for holography. In particular I describe how AdS black hole bound states can be used to model glassy systems and how the dual field theory description helps in tackling fundamental issues of black hole physics such as the statistical interpretation of black hole entropy. Progress in the study of the dynamics of black holes with supersymmetry breaking will be of particular interest.

Fabrizio Canfora

Centro de Estudios Científicos (CECS), Valdivia, Chile

Gravitating (almost) axisymmetric Hadronic tubes

In this talk I will show how to construct analytic solutions of the Einstein-Maxwell-Gauged-Non-Linear-Sigma model in (3+1)-dimensions representing the gravitational and electromagnetic fields of Hadronic tubes carrying a superconducting current. In this theory, the non-linear sigma model with internal group SU(2) is minimally coupled both to General Relativity and to Maxwell theory as the SU(2)-valued scalar field represents Pions. The solutions presented in the talk possess a non-trivial topological charge (the third homotopy class) which prevent them from decaying into the trivial solution. The topological charge can be interpreted as the Baryonic charge of the configurations. Such solutions also carry a superconductive current. Both the current and the energy-density are mostly non-zero within a tube-shaped region. All the curvature invariants are axisymmetric and regular (so these configurations can be considered as gravitating hadronic solitons). However, the metric itself is not axisymmetric. Some phenomenological implications will be discussed.

Francesco Belgiorno

Politecnico di Milano, Milano, Italy

Analog Hawking Effect: A Master Equation

In the framework of Analogue Gravity, we propose a fourth order ordinary differential equation, which allows to discuss the problem of Hawking radiation in presence of dispersion in a unified way, encompassing fluids and dielectric media.

Sumanta Chakraborty

Indian Association for the Cultivation of Science, Kolkata, India

From Boundary Action to Thermodynamics in Gravity

In the first part of my talk I will discuss the variational principle for general relativity in some detail. In particular, I will try to arrive at the correct action principle for general relativity in the presence of null boundaries. Possible generalization to Lovelock theories will also be presented. I will show how the action principle inherits a natural thermodynamic interpretation. Following which, I will discuss the thermodynamics of null surfaces, in particular, the black hole horizon in the presence of Fermionic fields, which will lead to several subtle effects. I will show that despite such subtlety it is possible to arrive at a first law of black hole thermodynamics in the presence of Fermionic fields. Implications will also be discussed.

Marcello Ortaggio

Czech Academy of Sciences, Prague, Czech Republic

Universal black holes

We prove that a generalized Schwarzschild-like ansatz can be consistently employed to construct d-dimensional static vacuum black hole solutions in any metric theory of gravity for which the Lagrangian is a scalar invariant constructed from the Riemann tensor and its covariant derivatives of arbitrary order. Namely, we show that, apart from containing two arbitrary functions a(r) and f(r) (essentially, the gtt and grr components), in any such theory the line-element may admit as a base space any isotropy-irreducible homogeneous space. Technically, this ensures that the field equations generically reduce to two ODEs for a(r) and f(r), and dramatically enlarges the space of black hole solutions and permitted horizon geometries for the considered theories. We then exemplify our results in concrete contexts by constructing solutions in particular theories such as Gauss-Bonnet, quadratic, F(R) and F(Lovelock) gravity, and certain conformal gravities.

Carlo Alberto Cremonini

Università degli Studi dell'Insubria, Como, Italy

Super Chern-Simons, A_∞-algebras and BV Formalism

We will present the formulations of 3-d Chern-Simons theory on a real supermanifold. After a brief introduction to form complexes in supergeometry, with particular attention to integration theory, we will construct SCS with pseudo-forms. This will introduce non-associative products and the gauge structure of an A_∞-algebra, analogous to the one emerging in Open Superstring Field Theory. Finally, we will discuss the BV formalism for this theory and the related L_∞ structure.

Harold Erbin

Politecnico di Torino, Torino, Italy

Machine learning for QFT

Machine learning has revolutionized most fields it has penetrated, and the range of its applications is growing rapidly. The last years has seen efforts towards bringing the tools of machine learning to lattice QFT. After giving a general idea of what machine learning is, I will present two recent results on lattice QFT: 1) computing the Casimir energy for a 3d QFT with arbitrary Dirichlet boundary conditions, 2) predicting the critical temperature of the confinement phase transition in 2+1 QED at different lattice sizes.

Anastasios Petkou

Aristotle University of Thessaloniki, Thessaloniki, Greece

Lessons from CFTs on nontrivial manifolds

Even if one knows everything for a conformal field theory on the infinite plane, new data are required to place the same theory in finitegeometries. This is a physically relevant question for finite temperature/finite-size critical systems. I will show in this talk how to apply an OPE inversion formula to thermal two-point functions of bosonic and fermionic CFTs in general odd dimensions. This allows us to analyze in detail the operator spectrum of these theories. The main result is that nontrivial thermal CFTs arise when the thermal mass satisfies an algebraic transcendental equation that ensures the absence of an infinite set of operators from the spectrum. The solutions of these gap equations for general odd dimensions are in general complex numbers and follow a particular pattern. I will argue that this pattern unveils the large-N vacuum structure of the corresponding theories at zero temperature.

Lucrezia Ravera

Politecnico di Torino, Torino, Italy

Chern-Simons formulation of non- and ultra-relativistic (super)gravity theories in 2+1 spacetime dimensions

Spacetime symmetries have played a fundamental role in the understanding of diverse physical theories, many of which are based on relativistic symmetries. However, in the literature models with non-relativistic symmetries have also been developed and analyzed, attracting some interest over recent years due to their utilities to approach strongly coupled condensed matter systems as well as non-relativistic effective field theories, gravity models, and holography. Concerning gravity, there are many different versions of non-relativistic gravity theories, invariant under distinct extensions of the Galilei symmetries, the latter arising when the velocity of light is sent to infinity (non-relativistic limit). On the other hand, there also exists another type of non-relativistic symmetry that has sporadically attracted some interest: the Carroll symmetries, which emerge when the velocity of light is sent to zero (ultra-relativistic limit). In this talk I will focus on the construction and analysis of three-dimensional non- and ultra-relativistic (super)gravity models described by Chern-Simons actions as gauge theories.

Adolfo Cisterna

Universidad Central de Chile, Santiago, Chile

Anti de-Sitter black strings for General Relativity and Lovelock gravities

In this talk we will show how to construct homogeneous anti de-Sitter black strings in General Relativity by using a suitable scalar dress (minimally coupled scalar fields) of the extended coordinates. We will show how to extend the procedure for the case of Gauss-Bonnet gravity and therefore for any Lovelock gravity, this by generalizing the scalar dress to include non-minimal coupling with curvature tensors. Finally we will comment about the stability of these solutions and how they are related with general compactifications of higher curvature theories on direct product spacetimes.

Alejandro Ruipérez Vicente

Instituto de Física Teórica, Madrid, Spain

α'-corrected heterotic backgrounds

I will talk about a recently constructed family of analytic α'-corrected solutions of the effective field theory of the heterotic string. These solutions preserve 1/4 of the supersymmetries of the theory and describe superpositions of a stack of solitonic 5-branes, a fundamental string with winding and momentum along a compact direction and, optionally, a Kaluza-Klein monopole. After compactification, particular members of this family describe extremal 3- and 4-charge black holes in 5 and 4 dimensions, respectively. I will focus mainly on the 4-dimensional ones, paying special attention to the so-called small black holes, which are 2-charge black holes with a singular (zero size) horizon in the zeroth-order (supergravity) approximation. I will argue that, contrary to what is often believed, the α'-corrections do not stretch the horizon and that the system remains singular even after the first-order α'-corrections are taken into account. Finally, if I have time, I will also discuss the recent construction (1905.00016[hep-th]) of supersymmetric rotating black holes in 5- and 4-dimensional gauged supergravity and its embedding in string theory.

Hugo A. Camargo

Max Planck Institute for Gravitational Physics, Potsdam, Germany

Complexity for Quantum Fields: Subregions, Mixed States and Purifications

In this talk we explore the notion of complexity in quantum field theories. We first apply the notion of circuit complexity to a quantum quench through a critical point in 1+1 dimensions. We apply this setup to a Gaussian state with two degrees of freedom, where we quantify the complexity of purification associated with a subregion, and show that complexity is capable of probing features to which the entanglement entropy is insensitive. We find that the complexity of subregions is subadditive, and comment on potential implications for holography. We also discuss upcoming work regarding the study of complexity of purification for mixed Gaussian states with a large number of degrees of freedom. In the second part of the talk, we enter the recent discussion involving the two definitions of complexity in field theories, namely circuit complexity and path integral complexity. We focus on two-dimensional conformal field theories (CFTs) where we provide a measure for the circuit complexity associated to the unnormalized thermal density matrix ρ=exp(-β H). We show that the Liouville action, which is the path integral complexity measure for ρ, is an approximation to a genuine circuit complexity measure.

Marco Astorino

INFN sez. Milano, Milan, Italy

Solution Generating Technique in GR, Ehlers transformation and the Majumdar-Papapetrou-NUT spacetime

After a brief introduction of the Ernst solution generating technique in General Relativity, the transformation which adds (or removes) NUT charge to electrovacuum, axisymmetric and stationary space-times is analysed. A new Ehlers transformation, more precise in the presence of the Maxwell electromagnetic field, is presented. An analytical exact solution is built by adding the NUT parameter to the double Reissner- -Nordstrom black hole. It describes a pair of rotating and charged black holes at equilibrium. From the near-horizon analysis, its microscopic entropy, according to the Kerr/CFT correspondence, is found and the second law of black hole thermodynamics is discussed.

Nicolò Petri

Universidad de Oviedo, Oviedo, Spain

Why Nothing does Matter: AdS Instabilities and de Sitter Cosmologies

One of the most relevant problems in theoretical physics is the construction of realistic cosmological models in a fundamental setup where the gravitational field has a fully consistent quantum completion. In this talk I will present a new approach to this problem in which de Sitter emerges as the geometry describing the non-perturbative instabilities of higher-dimensional AdS vacua in General Relativity plus a negative cosmological constant. These instabilities will be studied in the semi-classical approximation by considering a new class of gravitational instantons describing a spontaneous process of nucleation of "bubbles of nothing" into the AdS background. These bubbles are expanding in time and they have only an "exterior", in other words they completely destroy the AdS vacuum by making it decay literally "into nothing". The crucial feature of these instabilities is given by the fact that an observer living on the surface of these bubbles will experience a positive cosmological constant.

Marco Fazzi

Technion - Israel Institute of Technology, Haifa, Israel

High electric charges from M-theory

M-theory on a Calabi-Yau threefold admitting a small resolution gives rise to an Abelian vector multiplet and a charged hyper. I will introduce into this picture a procedure to construct threefolds that naturally host matter with electric charges up to six. These are built as families of Du Val ADE surfaces, and the possible charges correspond to the Dynkin labels of the adjoint of the ADE algebra. I will give a procedure for constructing higher-charge cases at will.

Davide Forcella

APC - Université Paris Diderot, Paris, France

Causality, Non-Locality and Exotic waves phenomena

Exotic waves phenomena have recently attracted theoretical and experimental research and foster technological innovation. Nevertheless the possibility and conditions for the existence of such phenomena have been rarely investigated from first principle, while a phenomenological approach has been privileged. In this talk we focus on a peculiar exotic phenomenon: negative refraction for which energy flux can be opposite to certain range of phase velocities, and show that fundamental principle, such as causality, provide important necessary, and in certain cases sufficient conditions, for the existence or not of such phenomena. In particular, while the experimental and phenomenological approach have been naturally focused on transparent and local media, we show that both dissipation and spatial non locality are necessary conditions for the existence of negative refraction. We also provides a sufficient condition in materials with weak spatial non locality. These fundamental results have broad implications in the theoretical and practical analyses of negative refraction of electromagnetic and other kinds of waves. It moreover shows the interest of a fundamental approach towards technology/low energy physics that can reveals new constraints and phenomena.

Nicolò Petri

Boğaziçi University, Istanbul, Turkey

The massive IIA origin of 2d CFTs

Even if AdS3/CFT2 holography has been intensively studied in literature, the construction of 2d CFTs in string theory is still rather obscure. In this talk I will discuss some insights in this direction coming from a new class of exact AdS3 solutions in massive IIA supergravity. Within this class, some of these 10d backgrounds are derived by uplifting particular warped AdS3 solutions in 7d and 6d gauged supergravities featuring respectively AdS7 and AdS6 asymptotics. In these cases the corresponding dual 2d SCFTs are realized as conformal defects within the higher-dimensional SCFTs dual to the asymptotics. I will discuss about the brane intersections underlying these solutions and, in particular, on how the emergence of AdS3 in massive IIA is deeply related to D2 branes. To support this statement I will present a very simple brane solution involving only D2 branes and O8 planes with near-horizon given by a warped product of AdS3 with a squashed 7-sphere as internal space. In spite of the simplicity of this supergravity solution, the construction of the dual SCFT 2d is quite problematic, therefore I will conclude discussing these issues and the possible strategies to get rid of them.

Pablo Bueno

KU Leuven, Leuven, Belgium

Higher-order gravities, black holes and holography

Higher-curvature gravities can be used to test the genericness of various features present in general relativity. In particular, they define holographic toy models inequivalent to Einstein gravity which (sometimes) can be used to learn general lessons about CFTs beyond holography. In this talk I will review the recent identification of a new class of such theories whose special properties makes them amenable for this kind of applications. Focusing in four dimensions, I will argue that generalizations of the Schwarzschild black hole become thermodynamically stable below certain mass for an infinite family of ghost-free theories involving terms of arbitrarily high order in curvature, dramatically changing their evaporation process. As a further application, I will discuss a new conjecture concerning the free energy of general CFTs on squashed spheres arising from the holographic result in one of our new theories along with free-field calculations.

Daniele Musso

Instituto Galego de Fisica de Altas Enerxias & Universidad de Santiago de Compostela, Santiago de Compostela, Spain

Completing the hydrodynamic description of bad metals from above and from below

Bad metals are clean systems with poor conductivity that do not admit a description in terms of long-lived degrees of freedom. Hydrodynamics can account for bad metal phenomenology without providing a precise explanation of the dynamical mechanism at work. Holography offers UV completions which allow to relate the behaviour of the hydrodynamic parameters (such as the rate of momentum dissipation) to the UV details of the model, like the sources and the symmetry pattern. Following the RG flow, one can explicitly get the T dependence of the hydro parameters. One can study the higher non-hydro modes too. Complementary, holography is useful also in completing hydrodynamics from 'below', helping in the construction of zero temperature effective theories and candidate ground states to connect the hydrodynamic features to the structure of Goldstone low energy modes.

Gabriele Tartaglino-Mazzucchelli

KU Leuven, Leuven, Belgium

Higher-derivative invariants in 6D supergravity

I will review the recent construction of new higher-derivative invariants for supergravity in six dimensions (6D). This is based on an interplay between the superconformal tensor calculus, the superform approach to construct supersymmetric invariants and novel off-shell superspace techniques. I will first outline how to classify curvature squared invariants in 6D N=(1,0) Poincar?supergravity, including the Gauss-Bonnet invariant which describes α'-corrections to the low-energy limit of compactified string theory. Next, time permitting, I will show how to derive the two (six-derivatives) actions for N=(1,0) conformal supergravity that describe the type B conformal anomalies in 6D. I will then comment on applications of these invariants including the description of the single N=(2,0) conformal supergravity invariant.

Pedro Ramírez

INFN sez. Milano, Milan, Italy

α'-corrected black holes in Heterotic String Theory

I will present the first-order in α' corrections to a 3-charge black hole in Heterotic Superstring Theory with the possible addition of SU(2) Yang-Mills fields. All the calculations are carried out in the 10-dimensional theory, avoiding the problems posed by the dimensional reduction or the supersymmetry completions of 5-dimensional actions. Since the solution covers the asymptotically-flat region and not just the near-horizon region, we can compute the F1, S5 and instanton charges directly. Furthermore, using α'-corrected Buscher T-duality rules we can determine the momentum charge through its relation with the F1 charge. We compute the mass, area and the corrections to the entropy using Wald's formula, which can be applied to the case at hands.

Anastasios Petkou

Aristotle University ( Thessaloniki, Greece)

The fermion-boson map with imaginary chemical potential in general dimensions

In the presence of finite temperature and imaginary chemical potential, the three-dimensional Gross-Neveu and CP^{N-1} models exhibit a remarkable fermion-boson duality. We discuss this in detail, showing that the complicated phase strauctures of the corresponding theories are mapped into each other. We observe the presence of thermal windows, inside which the two models exhibit statistical transmutation. Remarkably, the gap equations and free energies can be written in terms of the celebrated Bloch-Wigner-Ramakrishna functions generalized by Zagier. This observation allows us to attempt to ask whether similar fermion-boson maps exists for higher dimensions. We present some very positive preliminary results in this direction, which include - en passant - a curious semi-analytic conjecture for the zeros of the Clausen functions on the unit circle.

Lucrezia Ravera

INFN sez. Milano, Milan, Italy

Hidden Gauge Structure of Supersymmetric Free Differential Algebras and Hidden Symmetries of D=11 Supergravity

I will present a detailed investigation of the gauge algebra hidden in all Free Differential Algebras in supersymmetric theories, focusing, in particular, on the hidden symmetries of D=11 supergravity.

Andrea Fontanella

University of Surrey (Guildford, United Kingdom)

Heterotic near-horizon geometries

In this talk, I shall discuss about geometric properties of black hole horizons, both supersymmetric and non. In the first part, I will focus on how string corrections affect properties of supersymmetric near-horizon geometries. I will consider whether there exists a doubling of the number of preserved supersymmetries, the so-called supersymmetry enhancement. Standard global theorems, such as the Lichnerowicz theorem, crucial to establish supersymmetry enhancement, will be presented. In the second part, I will consider the inverse problem of determining all black hole solutions associated to a prescribed near-horizon geometry. I will expand the horizon fields at first order in the radial coordinate, the so-called moduli, and show that the moduli must satisfy a system of elliptic PDEs, which implies that the moduli space is finite dimensional. The talk is based on arXiv:1605.05635 [hep-th] and arXiv:1610.09949 [hep-th].

Antonio Amariti

Milan University (Milan, Italy)

Modern aspects of 3d N=2 QFTs

I will review some modern approaches to the analysis of supersymmetric field theories in (2+1)-dimensions with four supercharges. The presence of a CS action and of a Coulomb branch together with the absence of global anomalies and of a holographic dual description, have made the analysis of strong coupling complicated and only few aspects of these models have been investigated in the past. More recently, especially thanks to localization, many observable became accessible, boosting the number of non-perturbative and exact results. I will review some of these new results, focusing on the role played by the one-loop exact partition function obtained by localization on the three sphere.

Anastasios Petkou

Aristotle University, Thessaloniki, Greece

Generalized Wilson-Fisher critical points from conformal symmetry

Generalized massless free theories can be consistently defined as CFTs. Their nearby Wilson-Fisher critical points can be studied using the analytic structure of generic conformal blocks. This way we obtain the leading order nontrivial anomalous dimensions and critical couplings for wide classes of theories, including generalized multicritical points, O(N) models and modes with multiple marginal deformations. Our results reveal an intriguing underlying structure in the web of generalized CFTs which is intimately connected to higher-spin theory.

Saeedeh Sadeghian

Institute for Research in Fundamental Sciences (IPM), Tehran, Iran

Extremal Vanishing Horizon Black Holes

It is established that black holes may be viewed as thermodynamic systems. Extremal black holes, which are at zero temperature, still show interesting (thermodynamical) features and have attracted a lot of attention: some uniqueness theorems on near horizon geometry of them have been proved, indicating presence of an AdS_2 factor in these geometries. There is a class of extremal black holes for which entropy vanishes (have vanishing horizon area). Here we present three theorems about the near horizon geometry of such Extremal Vanishing Horizon (EVH) black holes: I) Near horizon EVH geometry contains a three dimensional maximally symmetric subspace. II) For theories which satisfy strong energy condition, this 3d subspace generically is a locally AdS_3 space. III) In near horizon, near-EVH black hole this AdS_3 geometry turns into a BTZ black hole. Motivated by the fact that any near horizon geometry is a solution to the theory to which its parent black hole is a solution, we construct solutions in 4 and 5 dimensional Einstein-Maxwell-Scalar theories and gauged supergravities and also in d dimensional pure Einstein theory. We prove a special rigidity theorem: all solutions to five dimensional Einstein-Maxwell- theories which are SO(2,2) symmetric, necessary have an extra axial U(1) symmetry. At the end, we relate the near horizon geometries of known EVH black holes to the SO(2,2) solutions we have classified earlier.

Alessio Marrani

Padua University

Freudenthal and Exceptional : Symmetries of Gravity and Black Hole Entropy

Freudenthal duality can be defined as an anti-involutive, non-linear map acting on symplectic spaces. It was originally introduced in four-dimensional Maxwell-Einstein theories coupled to non-linear sigma models of scalar fields. After a general introduction on some aspects of extended (super)gravity theories and the structure of their U-orbits, I will consider their U-duality Lie groups "of type E7", and the corresponding notion of Freudenthal duality. I will elucidate and comment on the relation between the Hessian of the black hole entropy and the pseudo-Riemannian, rigid, para-special Kaehler metric of the pre-homogeneous vector spaces associated to the U-orbits. I will conclude with some hints for further future developments.

Anastasios

Aristotle University, Thessaloniki, Greece

Integrable Holographic Fluids

I describe the recent progress in understanding which set of boundary data yield exact 4-dimensional Einstein spaces that are algebraically special. The corresponding boundary data can be viewed, in most cases, as 3-dimensional relativistic fluids, not necessarily in the hydrodynamic regime.

Stephane Detournay

Université Libre de Bruxelles

Asymptotic Symmetries, Bekenstein-Hawking Entropy, and Two-Dimensional Field Theories

The concept of asymptotic symmetries has played a significant role in the discovery and subsequent developments of gauge/gravity (or holographic) dualities. Examples include the analysis of Brown-Henneaux on asymptotic symmetries of AdS3 spaces, pointing at the existence of a two-dimensional Conformal Field Theory dual to quantum gravity in AdS3, or more recently the Kerr/CFT correspondence. After briefly reviewing the points mentioned above, I will discuss new holographic scenarios emerging by following the same philosophy. I will describe the asymptotic symmetries of certain classes of non-asymptotically AdS spaces (e.g. flat spaces and toy models for extreme Kerr black holes) and analyze the implications for their potential field theory duals. In particular, I will show that the corresponding field theories admit Cardy-like regimes allowing to derive universal formulas for their degeneracy of states, which exactly reproduce the Bekenstein- Hawking entropy of the corresponding gravitational solutions - much like the BTZ black hole entropy can be reproduced by a Cardy formula.

Keiichi Maeda

Waseda University (Tokyo, Japan)

Dark energy and dark matter in the ghost-free bigravity theory

We study dynamics of Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime based on the ghost-free bigravity theory. We find two stable attractors for spacetime with "twin" dust matter fields: One is de Sitter accelerating universe and the other is matter dominated universe. A considerable number of initial data leads to de Sitter universe, although we also find matter dominated universe or spacetime with a future singularity for some initial data. The cosmic no-hair conjecture does not exactly hold, but the Lambda-CDM model is found naturally as an attractor. We also analyze the possibility for the twin matter fluid to be dark matter in "our world". Dark matter appears as the galactic missing mass, is required in the cosmic structure formation and is found in the cosmic pie (the content of the Universe). We show the bigravity theory can also explain those facts by twin matter fluid when the Compton wavelength of the massive graviton is shorter than a galactic scale.

Seiju Ohashi

KEK, Tsukuba, Japan

Multi-scalar extension of Horndeski Theory

Horndeski theory is the most general scalar-tensor theory with second-order field equations, and recently it is attracting attention in the context of cosmology. We discuss extension of this theory to the multi-scalar field case. It was shown that straightforward extension of the theory, so-called generalized covariant multi-Galileon theory, is not the most general one. In this talk, we explain our attempt toward construction of the most general theory based on Horndeski's strategy.

Alessio Marrani

Università di Padova

Supersymmetry, Gravity and Attractors

I will present a general survey of basic facts on the attractor dynamics in extremal black hole solutions of locally supersymmetric theories of gravity. In particular, I will consider the general issue of stability of attractor points, and the classification of U-duality charge orbits and of the corresponding "attractor moduli spaces" in four-dimensional theories based on symmetric scalar manifolds. Some brief remarks on current and future developments will be made, as well.

Glenn Barnich

Université Libre de Bruxelles & International Solvay Institutes (Bruxelles, Belgium)

Holographic aspects of gravity in four and three dimensions

After a brief review of the symmetry groups of asymptotically AdS and flat spacetimes, I will discuss in some detail the status of the four dimensional flat case. In particular, I will explain why current algebras need to replace the more traditional algebra of ADM-type charges and briefly comment on the relation to soft theorems. In three dimensions, more results are available. In particular, the complete solution space is entirely controlled by group theory, the coadjoint representation of the Virasoro group in the AdS case and of the BMS$_3$ group in the flat case. This allows one for instance to prove positive energy theorems by using well-established results on the co-adjoint orbits of the Virasoro group.

Harold Erbin

LPTHE, Paris 6 University (Paris, France)

Abelian Hypermultiplet Gaugings and BPS Vacua in N = 2 Supergravity

We analyze the gauging of Abelian isometries on the hypermultiplet scalar manifolds of N = 2 supergravity in four dimensions. This involves a study of symmetric special quaternionic-Kaehler manifolds, building on the work of de Wit and Van Proeyen. In particular we compute the general set of Killing prepotentials and associated compensators for these manifolds. This allows us to glean new insights about AdS4 vacua which preserve the full N = 2 supersymmetry as well as BPS static black hole horizons. (arXiv:1409.6310)

Christos Charmousis

CNRS, LPT, Université Paris Sud

Fake hair for black holes

We will review modification of gravity theories and in particular scalar tensor theories, the mildest of modifications where apart from the metric we have an additional interacting scalar field coupling to the metric tensor. By means of a theorem given by Horndeski back in 1974 we will show the most general of these theories. Horndeski theory is often dubbed Galileon theory. We will examine a particular sub class of Horndeski theory which has interesting properties with respect to the cosmological constant problem. We will then find black hole solutions of this subclass which in some cases will be identical to GR solutions. The novel ingredient will be the presence of a time and space dependent scalar. As we will see time dependence will bifurcate no hair theorems and provide for the first time regular scalar tensor black holes with a non trivial scalar field.

Rodrigo Olea

Universidad Andres Bello

On renormalized AdS action and Critical Gravity

It can be shown that the renormalized action for AdS gravity in even spacetime dimensions is equivalent --on shell-- to a polynomial of the Weyl tensor, whose first non-vanishing term is Weyl^2. Remarkably enough, the coupling of this last term coincides with the one that appears in Critical Gravity.

Marco Caldarelli

University of Southampton, UK

AdS/Ricci-flat correspondence and a few applications

I will present a map connecting a class of Ricci-flat solutions to a class of asymptotically AdS spacetimes. In particular, it links Minkowski spacetime to AdS on a torus, the holographic stress energy tensor of AdS to the stress energy tensor due to a brane localized in the interior of spacetime and AdS black branes to (asymptotically flat) Schwarzschild black branes. Applying it to the known solutions describing the hydrodynamic regime in AdS/CFT, we compute the dispersion relation of the Gregory-Laflamme unstable modes of the black string finding remarkable agreement with numerical data, and obtain the fluid dual to Rindler spacetime, showing how its transport coefficients follow from the AdS ones. More generally, this correspondence provides a starting point for developing a detailed holographic dictionary for this class of Ricci-flat spacetimes, and suggests a possible origin for the hidden conformal symmetry recently observed in black holes.

Masato Nozawa

KEK, Tsukuba, Japan

Classification and stability of vacua in N=8 gauged supergravity

We present a systematic study of critical points for the SL(8,R)-type gauging in four dimensional maximal gauged supergravity. We determine all the possible vacua for which the origin of the moduli space becomes a critical point. We formulate a new tool which enables us to find analytically the mass spectrum of the corresponding vacua in terms of eigenvalues of the embedding tensor. When the cosmological constant is nonvanishing, it turns out that many vacua obtained by the dyonic embedding admit a single deformation parameter of the theory, in agreement with the results of the recent paper by Dall'Agata, Inverso and Trigiante [arXiv:1209.0760]. Nevertheless, it is shown that the resulting mass spectrum is independent of the deformation parameter and can be classified according to the unbroken gauge symmetry at the vacua, rather than the underlying gauging. We also show that the generic Minkowski vacua exhibit instability.

Claudius Klare

Milano Bicocca

Supersymmetry on Curved Spaces and Holography

Supersymmetric field theories on curves spaces have recently attracted a lot of interest in the context of localization and exact results in QFT. I will discuss the existence of superconformal and supersymmetric theories on certain Euclidean and Lorentzian manifolds, with a view towards holographic applications. In particular, I will present the restrictions upon the space-time geometry coming from supersymmetry. In the superconformal case, I will show how the (possibly curved) space-time arises as the boundary geometry of a gravity dual.

Christos Charmousis

CNRS

Hairy black holes

We will report on charged 4 dimensional black hole solutions in ads space which are dressed by axionic fields. We will show how axions regularise black hole RN type geometries by providing a stealth negative curvature term in the black hole lapse function. Using this fact, we will construct hairy versions of this charged black holes with planar horizons. These, as we will see, generalise the MTZ hairy black holes with a conformally coupled scalar. We will then examine thermodynamic competition in between the hairy and bald black holes discussing possible relations to the holographic superconductor paradigm.

Andrea Borghese

Groningen

The Many Surprises of Maximal Supergravity

More than thirty years after its inception, maximal D=4 supergravity continues to be a fascinating theoretical edifice. Interesting open issues include the possible finiteness of the ungauged version, the connection to the worldvolume theory of M2-branes and its possible holographic applications in condensed matter systems. The first example of gauged maximal supergravity dates back to Cremmer and Julia in 1979. There an SO(8) inside of the full duality group of the theory was promoted to a local symmetry group. The theory with it's vacuum structure was supposed to be unique. A few weeks ago it has been discovered that this guess is indeed wrong. There is a whole class of SO(8) gauged N=8 supergravities. This seems to be true for many other types of gaugings opening interesting new possibilities. I will briefly review the basic ingredients necessary in order to construct the theory and explain these new interesting findings.

Antoine Van Proeyen

KU Leuven

Superconformal methods for super-Poincare theories

Superconformal symmetry is the largest spacetime symmetry that one can impose on a field theory. For the construction of many supergravity theories, especially those with matter couplings, it is useful to start with a superconformal invariant action, and then break symmetries to remain with super-Poincar?gravity. This method works also for the construction of higher-derivative actions. More speculative, it can also shed light on quantum aspects of supergravity.

Tassos Petkou

University of Thessaloniki

Aspects of the HS/O(N) Correspondence

I discuss new developments in the Higher-Spin/O(N) Vector Model correspondence. In particular, I discuss the role of bulk singleton fields in describing the breaking of O(N) symmetry in the boundary by a novel mechanism which seems to be unique to vector model holography.

Mirjam Cvetic

University of Pennsylvania

Conformal Symmetry of General Asymptotically Minkowski Black Holes

We review properties of multi-charged rotating black holes in asymptotically Minkowski (and anti-deSitter) space-times, as solutions of maximally supersymmetric compactifications of String Theory. We focus on recent progress in deriving the conformal invariance and the microscopics of general, asymptotically Minkowski rotating black holes in four- and five-dimensions.

George Papadopoulos

King's College London

Geometry of supergravity horizons

Black holes, branes and other string and M-theory solitons exhibit horizons. The investigation of these horizons has yielded important results like the thermodynamics of black holes and AdS/CFT. I shall present the classification of horizon geometries in heterotic, IIB and 11-dimensional supergravities. I shall demonstrate that they admit novel geometries which recently have found applications in differential geometry.

Rodgrigo Olea

Universidad Andres Bello

Conformal Mass in AdS gravity

Kounterterm regularization in AdS gravity considers the addition of boundary terms which is a given polynomial in the extrinsic and intrinsic curvatures. We provide an explicit comparison between the conserved charges derived from Kounterterm method and the Ashtekhar-Magnon-Das (conformal) mass definition for asymptotically AdS spacetimes.

Gianguido Dall'Agata

Padova

New vacua from M-theory reductions

I will discuss a new method to find vacua of maximal gauged supergravity and its application to M-theory reductions. I will show how to produce interesting Minkowski vacua with partial SUSY breaking using locally geometric compactifications and I will discuss new non-supersymmetric Anti-de Sitter vacua and possible applications in the context of the gauge/gravity correspondence.

Suresh Nampuri

LPTENS Paris

Nernst branes in 4d gauged supergravity

We study static black brane solutions in the context of N = 2 U(1) gauged supergravity in four dimensions. Using the formalism of first-order flow equations, we construct novel extremal black brane solutions including examples of Nernst branes, i.e. extremal black brane solutions with vanishing entropy density. We also discuss a class of non- extremal generalizations which is captured by the first-order formalism.

Owen Vaughan

Liverpool, Dept. Maths.

The Hesse potential, the c-map and black hole solutions

I will present a new formulation of the local c-map, which makes use of the real formulation of special Kahler geometry associated with N = 2 supergravity. As an application I will explain how the temporal version of the c-map can be used as a solution generating technique, and present some new results regarding black hole solutions.

Patrick Meessen

Oviedo

On super symmetric Lorentzian Einstein-Weyl spaces

We consider weighted parallel spinors in Lorentzian Weyl geometry in arbitrary dimensions, choosing the weight such that the integrability condition for the existence of such a spinor, implies the geometry to be Einstein-Weyl. We then use techniques developed for the classification of supersymmetric solutions to supergravity theories to characterise those Lorentzian EW geometries that allow for a weighted parallel spinor, calling the resulting geometries supersymmetric. The overall result is that they are either conformally related to ordinary geometries admitting parallel spinors (w.r.t. the Levi-Civita connection) or are conformally related to certain Kundt spacetime. A full characterisation is obtained for the 4 and 6 dimensional cases.

Alessio Marrani

CERN PH-TH

Invariant Structures of Multi-Centered Black Holes

After a brief survey of multi-centered black hole physics, I will present some recent developments and advances in this field. I will report on the classification of 2-ctr. extremal black hole charge configurations through duality-invariant homogeneous polynomials, which are the generalization of the unique invariant quartic polynomial of the 1-ctr. case. A crucial role is played by an horizontal SL(p,R) symmetry group, which classifies invariants for p-ctr. black holes. For p=2, the horizontal-invariant with the lowest degree in charges is the symplectic product , known to control the mutual non-locality of the two centers. Within U-duality groups "of type E7", both reducible and irreducible symmetric supergravity models in four space-time dimensions will be considered, thus encompassing N = 2 "magical" and N = 8 maximal theories. Some basic references are 1] arXiv:1011.5864 [hep-th] 2] arXiv:1101.3496 [hep-th] 3] arXiv:1104.4652 [hep-th] 4] arXiv:1110.4004 [hep-th].

Tomas Ortin

IFT-UAM/CSIC

Non-extremal black holes of N=2, d=4 Supergravity

I will review the general construction of non-extremal black-hole solutions of N=2,d=4 supergravity coupled to vector multiplets, and their properties. I will describe the explicit solutions of a few models, their extremal (supersymmetric and non-supersymmetric) limits, entropies, non-extremality functions etc.

Giuseppe Dibitetto

Rijksuniversiteit Groningen (RUG)

Charting the Landscape of N=4 Compactifications

We analyse the vacuum structure of isotropic Z2 X Z2 flux compactifications, allowing for a single set of sources. Combining algebraic geometry with supergravity techniques, we are able to classify all vacua for both type IIA and IIB backgrounds with arbitrary gauge and geometric fluxes. Surprisingly, geometric IIA compactifications lead to a unique theory with four different vacua. In this case we also perform the general analysis allowing for sources compatible with minimal supersymmetry. Moreover, some relevant examples of type IIB non-geometric compactifications are studied. The computation of the full N=4 mass spectrum reveals the presence of a number of non-supersymmetric and nevertheless stable AdS4 vacua. In addition we find a novel dS4 solution based on a non-semisimple gauging.

Linda Uruchurtu Gomez

Imperial College London

Squashed Geometries via T-duality in String Theory

We construct explicit type II backgrounds containing squashed and warped anti-de Sitter spaces. These are obtained via T-duality from backgrounds with RR fields. We discuss their properties, including supersymmetry, hidden symmetries and classical integrability (without RR fields).

Masato Nozawa

Waseda University, Tokyo, Japan

Black holes in an expanding universe

Black holes in the isolated and stationary spacetimes have been intensively studied so far. They are completely characterized by conserved charges and exhausted by Kerr family. Black holes in non-isolated and dynamical background, on the other hand, have been less understood. In particular, the black-hole spacetime which is asymptotically FRW universe is of importance when discussing formation and evaporation of primordial black holes. In this talk, I will give a study on the causal structure of `black hole candidate' recently obtained by Ohta et al, which is specified by a set of harmonic functions. We established that this is the first realization of black hole in an decelerating universe satisfying appropriate physical conditions. This solution can be generalized to an arbitrary power law expansion and to any number of dimensions. We discuss physical properties and causal structures.

Jan Gutowski

King's College London

Supersymmetric Event Horizons in IIB Supergravity

We investigate the near horizon geometry of IIB supergravity black holes with non-vanishing 5-form flux preserving at least two supersymmetries. It is shown that there are three classes of solutions distinguished by the choice of Killing spinors. We find that the spatial horizon sections of the class of solutions with an SU(4) invariant pure Killing spinor are hermitian manifolds and admit a hidden Kahler with torsion geometry compatible with the SU(4) structure. A number of examples of solutions will be given.

Anastasios Petkou

University of Crete

Zermelo-Randers duality and Holographic Fluids

I discuss holographic fluids that live on background non-trivial stationary metrics. Using the Randers form of the metric we describe fluids with non-trivial vorticity. Using the Zermelo form of the metric we describe wave propagation in a flowing medium. As an example I discuss the generic Kerr-Taub-NUT AdS4 metrics and show that they provide the holographic description of cyclonic and vortex flow of 2+1 dimensional perfect fluids.

Vid Stojevic

University of Amsterdam

Torsionful Geometries in String Theory and the Relation to Non-geometry

I will talk about covariantly constant forms and almost product structures on torsionful geometries from both world-sheet and space time perspectives, and will discuss the importance of such non-integrable product structures for locally non-geometric compactifications of string theory. the talk is based on arxiv:1004.2824 and arxiv:0906.2028

Diederik Roest

Groningen

Metastable supersymmetry breaking in extended supergravity.

We discuss the possible stability of non-supersymmetric vacua of D=4 supergravity. First we review what is known about dS and non-SUSY AdS in different theories, and point out relations between these. In the main part of the talk we explain how one to make general statements on this issue, and generalise this to extended supergravities.

Pedro J. Silva

Barcellona

Dynamical gauge fields in AdS/condensed matter

Holographic superconductors have been studied so far in the absence of dynamical electromagnetic fields, namely in the limit in which they coincide with holographic superfluids. It is possible, however, to introduce dynamical gauge fields if a Neumann-type boundary condition is imposed on the AdS-boundary. In 3+1 dimensions, the dual theory is a 2+1 dimensional CFT whose spectrum contains a massless gauge field, signalling the emergence of a gauge symmetry. We study the impact of a dynamical gauge field in vortex configurations where it is known to significantly affect the energetics and phase transitions.

Giuseppe Dibitetto

University of Groningen

Maximal D=8 Gauged Supergravity

Maximal D=8 gauged supergravity theories have been partially classified in the past as compactifications of eleven-dimensional supergravity on a group manifold of dimension 3. By using the embedding tensor formalism, one is able to parametrize the most general gauging which satisfies all of the consistency constraints coming from supersymmetry. Finally, the full scalar potential is determined by making use of supersymmetry transformation rules.

Sergio Cacciatori

Universita' dell'Insubria

Analogue Hawking radiation in nonlinear optic media

Analogue gravity has been invented by Unruh in order to overcome the problem of performing a direct observation of the Hawking effect on astrophysical black holes. The main idea is to replace the black hole with a physical systems which reproduces the two fundamental ingredients responsible for the Hawking effect: a quantum field, and the presence of an horizon in an effective curved space-time background. The original proposal was to consider phonons in a stationary fluid. I will describe a simple model of analogue black holes, obtained by considering the electromagnetic field in a nonlinear Kerr medium (fused silica). I will show that thanks to Kerr nonlinearity, a strong pulse moving in the medium behaves as a black hole for the linear modes. The Hawking mechanism thus predicts that the black hole should evaporate by emitting a thermal spectrum. The presence of a dispersion modify the emission spectrum in a precise way, which has been recently observed in laboratory.

Oscar Dias

DAMTP, Centre for Mathematical Sciences, University of Cambridge

Kerr-CFT and gravitational perturbations

The Kerr-CFT correspondence recovers microscopically the Hawking-Bekenstein entropy of an extreme Kerr black hole. However it is supported by strong assumptions on the fall-off of metric perturbations. After a brief review of the Kerr/CFT, we investigate perturbations of the near-horizon extreme Kerr spacetime, to discuss its boundary conditions. The Teukolsky equation for a massless field of arbitrary spin is solved. Solutions fall into two classes: normal modes and traveling waves. Imposing suitable (outgoing) boundary conditions, we find that there are no unstable modes. The explicit form of metric perturbations is obtained using the Hertz potential formalism, and compared with the Kerr-CFT boundary conditions. The energy and angular momentum associated with scalar field and gravitational normal modes are calculated. The energy is positive in all cases. The behaviour of second order perturbations is discussed.

Glenn Barnich

Université Libre de Bruxelles and International Solvay Institutes

The BMS/CFT correspondence

After a reiew of symmetries and classical solutions involved in the AdS3/CFT2 correspondence, we apply a similar analysis to asymptotically flat spacetimes at null infinity in 3 and 4 dimensions. In the spirit of two di- mensional conformal field theory, the symmetry algebra of asymptotically flat spacetimes at null infinity in 4 dimensions is taken to be the semi-direct sum of supertranslations with infinitesimal local conformal transformations and not, as usually done, with the Lorentz algebra. As a first application, we derive how the symmetry algebra is realized on solution space. In particular, we work out the behavior of Bondi's news tensor, mass and angular momentum aspects under local conformal transformations.

Giuseppe Dibitetto

Groningen University

De Sitter solutions from IIA string theory

Peter Sloane

King's College London

Spinorial Geometry of Type I Supergravity

We review the spinorial geometry methods that were used to classify all supersymmetric solutions of the Type I/Heterotic supergravity. We emphasise the generic nature of the methodology and show how this may be applied to to problem of finding supersymmetric brane probe configurations in 11 dimensions.

So Young Pi

Boston University

Charge Fractionalization in a chiral gauge theory

The charge fractionalization phenomenon in two-dimensional space may be realized in graphene-like systems. Details of the Dirac-type theory that leads to this effect are described.

Roman Jackiw

Massachusetts Institute of Technology

Fractional Charge

Quantum theory has shown us that dynamical entities, which take continuous values in classical theory, may posses only discrete “quantized” values -- for example angular momentum, energy, etc. Here I describe a further quantum phenomenon affecting quantities that in a classical physics description take on discrete values -- for example particle number. In the quantum theory this integrality can be lost, becoming replaced by fractional or even continuous values. Physical realization of this “quantum weirdness” was first found in one-dimensional systems (polyacetylene) and then on the plane, in the quantum Hall effect. However, there is a significant difference between the mechanisms responsible for these two instances of fractionalization. The former arises in a T-invariant theory, while the latter requires T-violation, owing to the presence of a background magnetic field. Recently there has come the realization that a “Hall” - type effect can arise even with conserved T. Stimulated by this, there T-conserving planar models were found in which charge is fractionalized. These are based on theoretical extensions of graphene-like planar systems.

Tartaglino Mazzucchelli

University of Maryland

4D N=2 supergravity and projective superspace

Recently a new superspace formulation for off-shell four-dimensional N=2 matter-coupled supergravity has been developed making use of projective superspace. In this talk I first give a review of 4D flat projective superspace. I then describe the geometry of 4D N=2 conformal supergravity in superspace. Various off-shell matter multiplets in curved projective superspace are introduced and a manifestly locally supersymmetric and super-Weyl invariant action principle is given. I then describe the component reduction of the action and describe families of locally supersymmetric theories. The last part of the talk is devoted to 4D N=2 conformally flat superspaces. The example of the 4D N=2 anti-de Sitter superspace AdS^{4|8} will be presented in details.

Anastasios Petkou

University of Crete

A Vector Model Counting the Entropy of Membranes

I present a new proposal for a three-dimensional vector model that could account for the peculiar scaling of the entropy of M2 and M5 branes

Carlos Herdeiro

Porto University

Interacting black holes in four and five dimensions

I shall discuss the existence or otherwise of multi black hole configurations, as well as some physical properties, in four and five dimensions, with and without supersymmetry. In the supersymmetric case I shall focus on the five dimensional case and in the minimal supergravity theories with zero, negative and positive cosmological constant. In the non-supersymmetric case I shall focus on vacuum solutions generated by the inverse scattering technique, in particular the double Kerr, in 4 dimensions, and double Myers-Perry in 5 dimensions. In this case I shall be particularly interested in the interaction due to the rotational dragging between the two black holes.

Rodrigo Olea

Universidad Catolica de Valparaiso

Topological invariants, Kounterterms and self-duality in four-dimensional AdS gravity

We show that the addition of a topological invariant (Gauss-Bonnet term) to the anti-de Sitter (AdS) gravity action in four dimensions recovers the standard regularization given by holographic renormalization procedure. The comparison is carried out by considering the equivalent boundary formulation, which leads to counterterms with dependence on the extrinsic curvature K_{ij} (Kounterterm series). This crucial step makes possible the inclusion of an odd parity invariant (Pontryagin term) whose coupling is fixed by demanding an asymptotic (anti)self-dual condition on the Weyl tensor. This argument provides a simple derivation of the holographic stress tensor/Cotton tensor duality observed in recent literature in solitonic solutions and hydrodynamic models. A general prescription to generate the counterterm series for AdS gravity in any even dimension from the corresponding Euler term is also briefly discussed.

Sergio Cacciatori

Universit?dell'Insubria - Como

Analog gravity for optical systems

We discuss the experiments by Leonart and Philbin that aim to optically reproduce black hole configurations and to measure Hawking radiation. In particular, we shall consider a simple model (the light ball) that provides a rather precise prospect on experimental data.

Anastasios Petkou

University of Crete

The Gravity Dual of Parity Symmetry Breaking in AdS4/CFT3 Holography

We study four dimensional gravity with a negative cosmological constant deformed by the Nieh-Yan torsional topological invariant with a spacetime-dependent coefficient. We find an exact solution of the Euclidean system, which we call the torsion vortex, having two asymptotic AdS4 regimes supported by a pseudoscalar with a kink profile. We propose that the torsion vortex is the holographic dual of a three dimensional system that exhibits distinct parity breaking vacua. The torsion vortex represents a (holographic) transition between these distinct vacua. We expect that from the boundary point of view, the torsion vortex represents a `domain wall' between the two distinct vacua. From a bulk point of view, we point out an intriguing identification of the parameters of the torsion vortex with those of an Abrikosov vortex in a Type I superconductor. Following the analogy, we find that external Kalb-Ramond flux then appears to support bubbles of flat spacetime within an asymptotically AdS geometry.

Christoph Sieg

Niels Bohr International Academy

Gegenbauer polynomial x-space technique: High loop integrals

We extend and apply the Gegenbauer polynomial x-space technique to compute 3- and 4-dimensional high loop integrals.

Andrea Mauri

University of Crete

An introduction to BLG theory and its N=1 superfield formulation

Konstadinos Siampos

University of Patras

Bound states within AdS/CFT and their stability behavior

Constructing bound states potentials within the AdS/CFT correspondence often leads to discrepancies between field theory expectations and their dual gravitational description. Performing stability we show how to reconcile the predictions from the two sides.

Philippe Spindel

Mons University

The deformation quantizations of the hyperbolic plane

Our goal is to present the construction of (all) the invariant star-products on the hyperbolic plane as explicit solutions of a second order hyperbolic differential equation (revealing the existence of a ``dual\" metric canonically attached to the usual metric of $\\mbD$.). We present a unified method producing all quantization on the hyperbolic plane, and a purely geometric realisation of Weinstein's WKB quantization program.

Kellogg Stelle

Imperial College London

Is N=8 supergravity finite?

The problem of ultraviolet divergences is one of the oldest topics of discord in the history of quantum gravity, dating back into the 1930's. With the advent of supergravity, hopes were raised of a resolution to the divergence problem, but these were seemingly dashed by more careful study of what supersymmetry really implies. This topic has had a recent revival in the case of the maximal N=8 supergravity, for which a remarkable 3-loop calculation has now been completed using unitarity-based techniques, showing cancellations that would have been surprising at least in the 1980s. The question is whether this cancellation really represents a "miracle" that goes beyond the ultraviolet control of local supersymmetry. The question is still open. The talk will present the current evidence on the case.

Marco Caldarelli

University of Barcelona

Black holes and hydrodynamics

For many years it has been known that black holes behave in many respects like fluids: using the membrane paradigm, physics outside a black hole can be successfully modeled by a fluid membrane on the stretched horizon, while the Gregory-Laflamme instability of black strings has striking analogies with the Rayleigh-Plateau instability of fluids. These analogies become rigorous in presence of a negative cosmological constant. Indeed, large black holes in anti-de Sitter (AdS) spacetime have recently been shown to be dual to lumps of plasma described by Navier-Stokes equations on the boundary of AdS. This allows us to get new insight into the physics of the Gregory-Laflamme instability and to explore the phases of AdS black holes. In this talk I will first review higher-dimensional black holes, their instabilities and their relations with fluid dynamics. Then, I will analyse the properties of lumps of plasma dual to AdS black holes, and show how to obtain new results on the phases and stability properties of these black holes.

Serena Fagnocchi

Enrico Fermi Center and INFN Bologna

Acoustic Black Holes and the Correlations of the Hawking Radiation

Hawking radiation is the most famous and elusive prediction related to the formation of a black hole. Widely considered a milestone of theoretical physics, so far no experiment is confirming its existence. More fundamental than the theory it has been first derived, Hawking radiation shows up in any system able to reproduce the geometrical features of a forming black hole spacetime, for example supersonic flowing fluids (called acoustic black holes) where sound gets trapped exactly as light in a gravitational black hole region. A clear signature of Hawking radiation in acoustic black holes appears in the density correlation pattern, obtained analytically and confirmed via numerical simulations, opening the concrete possibility to observe it in real experiments in a near future. In this seminar the main features of the analogy between gravitation and hydrodynamics are reviewed, and the novel idea to reveal the presence of Hawking radiation in acoustic black holes via a correlation measurement is shown.

Finn Larsen

University of Michigan and CERN

The non-BPS branch of black holes in four dimensions

Extremal black holes with supersymmetry have been extensively studied. Those without supersymmetry have some similarities but also some qualitative differences. We construct these non-BPS black holes and discuss their physical properties.

Marco Maria Caldarelli

University of Barcelona

Phases of Black Holes in anti-de Sitter (second part)

I will review the hydrodynamic description of large black holes in AdS, and show that large magnetically charged black strings are dual to a magnetohydrodynamic theory on the boundary. Then, we will analyse the Gregory-Laflamme instability in this framework and discuss the phases of large asymptotically AdS black holes.

Marco Maria Caldarelli

University of Barcelona

Phases of Black Holes in anti-de Sitter

I will review the hydrodynamic description of large black holes in AdS, and show that large magnetically charged black strings are dual to a magnetohydrodynamic theory on the boundary. Then, we will analyse the Gregory-Laflamme instability in this framework and discuss the phases of large asymptotically AdS black holes.

Matias Leoni

University of Milan

4-point gluon scattering amplitude at strong coupling

We will discuss a recent result which shows how to compute the 4-point planar gluon scattering amplitude of N=4 SYM theory at strong coupling, by finding a minimal surface with appropriate boundary conditions in the string theory side. The result was found to agree with a previous conjecture by Bern, Dixon and Smirnov. This conjecture was justified by analyzing the iterative structure of the four point planar gluon scattering calculated by summing Feynman diagrams at 1, 2 and 3 loops in the field theory side.

Emanuele Zorzan

University of Milan

Flux compactifications from gauged supergravity (Report on the CERN school)

Francesco Fiamberti

University of Milan

Giant Magnons (Report on the CERN school)

Report on the CERN school

Sean McReynolds

University of Milan - Bicocca

Five-dimensional supergravity on a spacetime with boundaries

We discuss some features of 5D minimal supergravity coupled to vector and hypermultiplets on a background of the form R4 x S1\\Z_2. On the boundaries of the spacetime, half the supersymmetries are broken and half the field content lack propagating modes. Motivations for such models are for higher-dimensional GUTs, generalized Randall-Sundrum scenarios and 5D M-theory. The main issues we outline are constraints due to 'very special' target space geometry, anomalies in local bosonic and fermionic symmetries, and the possibility of singularities in the moduli space. The goal is to have a well-defined, supersymmetric, anomaly-free action (with supersymmetric ground states) useful for model building.

Carlo Alberto Ratti

University of Milan - Bicocca

Flavors and mesons in marginally deformed AdS/CFT

Flavor symmetry is an essential ingredient in models that describe dynamic of fundamental quarks coupled to a given gauge theory. In the quenching approximation this symmetry is related via AdS/CFT to probe branes placed in a dual background. From this setup one can extract many phenomenological predictions such as the mass levels of the mesonic states. After a description of the easiest Karch-Katz model, I will present how this construction can be extended to marginally deformed backgrounds and the physical properties that this flavored theory exhibits with respect to the undeformed case. In particular the main result is in the mesonic spectrum that shows a resolution of the degeneracies due to a Zeeman-like effect.

Marc Grisaru

Supergraphs and the S matrix

Rodrigo Olea

University of Milan

Universal Kounterterms in Lovelock AdS gravity

Lovelock theories consider higher curvature terms in the gravity action in a way they generalize two basic features of General Relativity to higher dimensions: general covariance and (at most) second-order field equations. When a (negative) cosmological constant is introduce, Lovelock gravity is not free of the usual divergences at the asymptotic region, so it needs to be regularized, e.g., to compute the corresponding black hole thermodynamics. In this seminar, we critically review two mechanisms of regularization for Lovelock-AdS gravity: 1) Dirichlet Counterterms, that adds to the bulk action covariant (intrinsic) functionals of the boundary metric $h_{ij}$ on top of a generalized Gibbons-Hawking term. 2) Kounterterms, that contain also a dependence on the extrinsic curvature $K_{ij}$ and whose origin is closely related to Chern-Simons forms and topological invariants, and whose form is preserved regardless the particular theory considered.

Dietmar Klemm

University of Milan

Introduction to spinorial geometry (second part)

We give a pedagogical introduction to spinorial geometry, which involves writing spinors as forms, and to the application of these techniques to the classification of supersymmetric solutions to supergravity and supersymmetric field theories.

Christoph Sieg

University of Milan

Computation of multi-loop integrals with the Gegenbauer polynomial x-space technique

The Gegenbauer polyomial x-space technique (GPXT) is a powerful technique to compute multi-loop integrals that also may contain non-trivial numerators. I will present the necessary tools to compute loop integrals also with non-trivial numerators and I will show how substantial information about the calculation can be read off directly from the so called angular diagram of a given Feynman diagram. I will also introduce a simplified IR regularization prescription which allows to compute the overall divergencies of loop integrals and significantly reduces the compexity of the calculation.

Dietmar Klemm

University of Milan

Introduction to spinorial geometry

We give a pedagogical introduction to spinorial geometry, which involves writing spinors as forms, and to the application of these techniques to the classification of supersymmetric solutions to supergravity and supersymmetric field theories.

Matteo Cardella

Hebrew Universty of Jerusalem

Closed String Tachyons on Bubbles of Nothing

Bubbles of Nothing are G.R. vacuum solutions obtained by a double analytic continuation on a black hole metric. A SUSY breaking mechanism by boundary conditions follows naturally from the geometry, and some of the bubble solutions support asymptotical SUSY. I discuss winding closed string tachyon condensation along a null direction of the bubble.

Sophie de Buyl

I.H.E.S. ? Bures sur Yvette

Towards a Kac-Moody invariant formulation of M-theory

Recent works suggest that the hyperbolic Kac-Moody algebra E10 could play a crucial role in the symmetry structure of M-theory. It has been argued that one way to exhibit the symmetry consists in rewriting the supergravity equations as the equations of motion of the non-linear sigma model E10/K(E10). In this talk, I will explain this construction and try to give an overview of the progress done in this direction.

Sophie de Buyl

I.H.E.S. ? Bures sur Yvette

Singularities, Cosmological Billiards and the Weyl group of hyperbolic Kac-Moody algebras

In the perspective of getting a better understanding of gravity, the study of extreme situations such as singularities is very instructive. In this talk, I will give a description of the general behaviour of the gravitational fields dynamics in the vicinity of a spacelike singularity as derived by Belinsky-Khalatnikov-Lifshitz, and explain how more recent works have established a connection between this behaviour and some hyperbolic Kac-Moody algebras. To be complete, I will review some basic definitions and examples of Kac-Moody algebras.

Alberto Santambrogio

University of Milan

The S-matrix of magnons in N=4 SYM

Francesco Fiamberti

University of Milan

Integrability in N=4 SYM theory

Prof. Pietro Fre'

Universita' di Torino

Cosmic Billiards and integrability of supergravity: an outlook

I will review the topic of smooth cosmic billiards

Andrea Mauri and Federico Elmetti

University of Milan

ICTP school report

A. Mauri: Dynamical supersymmetry breaking in metastable vacua F. Elmetti: Geometrically induced metastability

Rodrigo Olea

University of Milan

Kounterterms in Lovelock Gravity

Diego Mansi

University of Milan

Gravity Instantons

Prof. Dmitri Kazakov

JINR, Dubna

Renormalizable 1/N_f Expansion for Gauge Theories in Extra Dimensions

The previously developed renormalizable perturbative 1/N-expansion in higher dimensional scalar field theories is extended to gauge theories with fermions. It is based on the $1/N_f$-expansion and results in a logarithmically divergent perturbation theory in arbitrary high odd space-time dimension. Due to the self-interaction of non-Abelian fields the proposed recipe requires some modification which, however, does not change the main results. The new effective coupling is dimensionless and is running in accordance with the usual RG equations. The corresponding beta function is calculated in the leading order and is nonpolynomial in effective coupling. The original dimensionful gauge coupling plays a role of mass and is also logaritmically renormalized. Comments on the unitarity of the resulting theory are given.

Emanuele Zorzan

University of Milan

Kahler and Sasaki Geometries

Stephane Detournay

University of Milan

Godel black holes and asymptotic symmetries

I will remind Strominger's derivation of the BT(B)Z black hole entropy, based on asymptotic symmetries, and see how this could be extended to the case of Godel black holes.

Dietmar Klemm

University of Milan

Black holes and geometry

Anastasios Petkou

University of Crete

Instantons, Holography and the Instability of AdS4

I discuss the form and the holographic properties of an exact instanton solution of a consistent truncation of M-theory to 4 dimensions. I argue that this solution is an example of a non- perturbative instability of AdS4.

Christoph Sieg

University of Milan

Integrability and Ads/CFT

Patrick Meessen

Instituto de Fisica Teorica UAM/CSIC

Defrosting the hyperscalars

We will review the classification of supersymmetric solutions in ungauged supergravities with 8 supercharges, putting special emphasis on the hyperscalars.

Olivera Miskovic

Universidade Tecnica de Lisboa

Chern-Simons gravity with torsion and AdS/CFT correspondence

We explore the Conformal Field Theory living at the boundary of Chern-Simons gravity for AdS group, using the AdS/CFT correspondence. This is first order gravity where the well-defined Dirichlet problem requires to fix the vielbein and torsional degrees of freedom at the boundary. The associated holographic currents are the stress tensor and spin current coupled to the boundary metric and contorsion, respectively. In five dimensions, we derive these currents and we obtain the holografic Ward identities by looking at the bulk equations. We find that the conformal transformations in CFT appear as residue from the bulk AdS boosts, leading to the Weyl anomaly, and there are additional gauge transformations that give rise to the gauge anomaly. We also discuss the existence of chiral anomaly.

Geoffrey Compere

Universita' Libre de Bruxelles

Classical central extensions of asymptotic symmetries in three dimensions

T.B.A.

Cecilia Albertsson

Kyoto University

Worldsheet boundary conditions in Poisson-Lie T-duality

We apply canonical Poisson-Lie T-duality transformations to bosonic open string worldsheet boundary conditions, showing that the form of these conditions is invariant at the classical level, and therefore they are compatible with Poisson-Lie T-duality. In particular the conditions for conformal invariance are automatically preserved, rendering also the dual model conformal. The boundary conditions are defined in terms of a gluing matrix which encodes the properties of D-branes, and we derive the duality map for this matrix. We demonstrate explicitly the implications of this map for D-branes in a simple non-Abelian Drinfel'd double.

Luca Martucci

Institute for Theoretical Physics, K.U. Leuven

D-branes on N=1 backgrounds: generalized calibrations, superpotentials and D-terms

D-branes play a central role in string theory and in most of the derived phenomenologically relevant models. In this prospective, it is important to understand the physics of D-branes on Type II flux compactifications preserving minimal N=1 supersymmetry in four dimensions. I will discuss how it is possible to completely characterize general N=1 flux backgrounds in terms of a new kind of generalized calibrations. This allows to introduce general expressions for superpotentials and D-terms associated to the N=1 four-dimensional description of space-time filling D-branes. The direct link of superpotentials and D-terms with BPS domain walls and cosmic strings respectively is reproduced from the purely geometrical D-brane setting.

Prof. Irina Aref'eva

Steklov Math. Inst. of Moscow

Nonlocal String Field Theory Model for Cosmological Dark Energy

Recent astronomical observations show that the Universe is presently expanding with acceleration. This remarkable discovery suggests that the bulk of energy density in the Universe is gravitationally repulsive and appears like an unknown form of energy (dark energy) with negative pressure. A model for the dark energy which is nonlocal scalar field and which is derived from the string field theory describing the non-BPS brane decay will be considered. In this model the acceleration of the Universe is driven by a nonlocal stringy Higgs mechanism.

Aldo Cotrone

University of Barcelona

String splitting and strong coupling meson decay

In the first part of the talk, I give a general introduction to the main concepts of the string/gauge theory correspondence. In the second part, I study the decay of high spin mesons at strong coupling. The rate of the process is calculated by studying the splitting of a macroscopic string intersecting a D-brane. The result is applied to the case of mesons in N=4 SYM with a small number of flavors. I finally comment on the decay rate in a gravity dual of QCD.

Sergio Zerbini

Dept. of Physics - Trento University

Exact Black hole solutions with conformally coupled scalar fields

The issue related to violation of the no-hair theorem and n-dimensional black hole solutions in presence of scalar fields is revisited in the Conformal frame. The role of black holes entropy is discussed.

Mauro Brigante

Center for Theoretical Physics - Massachusetts Institute of Technology

Inheritance principle and non-renormalization theorems at finite temperature

We present a general proof of an \"inheritance principle\" satisfied by a weakly coupled SU(N) gauge theory with adjoint matter on a class of compact manifolds (like S^3). In the large N limit, finite temperature correlation functions of gauge invariant single-trace operators in the low temperature phase are related to those at zero temperature by summing over images of each operator in the Euclidean time direction. As a consequence, various non-renormalization theorems of N=4 Super-Yang-Mills theory on S^3 survive at finite temperature despite the fact that the conformal and supersymmetries are both broken.

Oprisa Dan

Ludwig-maximilians University - Munich

Six gluon open superstring disk amplitude, multiple hypergeometric series and Euler-Zagier sums

The six gluon disk amplitude is calculated in superstring theory. This amplitude probes the gauge interactions with six external legs on Dp-branes, in particular including e.g. F^6-terms. The full string S-matrix can be expressed by six generalized multiple hypergeometric functions (triple hypergeometric functions), which in the effective action play an important role in arranging the higher order alpha' gauge interaction terms with six external legs (like F^6, D^4 F^4, D^2 F^5, D^6 F^4, D^2 F^6, ...). A systematic and efficient method is found to calculate tree-level string amplitudes by equating seemingly different expressions for one and the same string S-matrix: Comparable to Riemann identities appearing in string-loop calculations, we find an intriguing way of using world-sheet supersymmetry to generate a system of non-trivial equations for string tree-level amplitudes. These equations result in algebraic identities between different multiple hypergeometric functions. Their (six-dimensional) solution gives the ingredients of the string S-matrix. We derive material relevant for any open string six-point scattering process: relations between triple hypergeometric functions, their integral representations and their alpha'-(momentum)-expansions given by (generalized) Euler-Zagier sums or (related) Witten zeta-functions.

Christoph Sieg

Physics Dept. - Theory Division - Universita' degli Studi di Milano

The holographic c-function

Augusto Sagnotti

Scuola Normale Superiore di Pisa

On higher spin geometry

We give a pedagogical introduction to the geometry of higher spin fields and to their applications to string theory.

Diederik Roest

Department of Mathematics - King's College - London

The spinorial geometry approach to the classification of supersymmetric solutions

Rodrigo Olea

Physics Dept. - P. Universidad Catolica de Chile

An alternative regularization scheme in AdS gravity

A background-independent, Lorentz-covariant approach to compute conserved charges in AdS gravity, alternative to the standard counterterms method, is presented. A set of boundary conditions on the asymptotic extrinsic and Lorentz curvature, rather than a Dirichlet boundary condition on the metric is used. With a given prescription of the boundary term, a well-defined action principle in any dimension is obtained. The same boundary term regularizes the Euclidean action and gives the correct black hole thermodynamics. The conserved charges are obtained from the asymptotic symmetries through Noether theorem without reference to any background. For topological AdS black holes the vacuum energy matches the expression conjectured by Emparan, Johnson and Myers for all odd dimensions.

Panagiota Kanti

Dept. of Mathematical Sciences - University of Durham

Creation and evaporation of higher-dimensional black holes

In the context of theories postulating the existence of additional spacelike dimensions, the possibility of creating a black hole during trans-planckian particle collisions is significantly enhanced. At the same time, the chances of detecting the ensuing emission of Hawking radiation, as these black holes rapidly decay, are also increased. As our results show, the spectrum of Hawking radiation, upon detection, could be an extremely rich source of information for important topological properties of our spacetime, such as its dimensionality and the existence of a cosmological constant.

Matteo Boni

Physics Dept. - Theory Division - Universita' degli Studi di Milano

AdS bubbling and D1-D5 systems

Matteo Cardella

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Scherk-Schwarz breaking, intersecting branes and non-supersymmetric string vacua

Marc Grisaru

McGill University

The S-matrix in the XXI century

This is an overview of some topics, old and new, concerning scattering amplitudes: a) supersymmetry and helicity conservation; b) multigluons trees and loops; c) cut-constructible diagrams; d) Witten's twistor approach.

Sergio Cacciatori

Mathematics Dept. - Universita' degli Studi di Milano

WZW models with boundary

Diego Mansi

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Gravitational Chern-Simons theories

Dario Melis

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Non-AdS/Non-CFT Correspondence

Gabriele Ferretti

Inst. for Theoretical Physics - Chalmers University - Goteborg

Spin chains and QCD

We present some recent results on the renormalization properties of composite operators in QCD and their relation to spin chains. The main motivation is to try to identify the worldsheet degrees of freedom of the QCD string.

Marco Caldarelli

Physics Dept. - Theory Division - Universita' degli Studi di Milano

1/2 BPS sector of supergravity (Ref.: hep-th/0502104)

Andrea Cappelli

INFN - Firenze

Teoria di campo non-commutativa ed effetto Hall quantistico

Si discute la proposta di Susskind di descrivere l'effetto Hall frazionario con la teoria di Chern-Simons non-commutativa e si analizza il modello di matrici corrispondente. Si deriva la funzione d'onda di Laughlin e si discutono gli aspetti tecnici e fisici della teoria quantistica e non-commutativa.

Alex Giacomini

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Two dimensional conformal symmetry and the microscopic interpretation of black hole entropy

Marcello Musso

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Stochastic Inflation

Jan Gutowski

Mathematical Institute, University of Oxford

Supersymmetric Black Rings

The recent discovery of supersymmetric black ring solutions has important implications for black hole uniqueness and other aspects of black hole physics in higher dimensions. The construction of these solutions is investigated, and a generalization of the single ring solution to a system of concentric (multi-charge) rings is presented. The entropy of some of these solutions is particularly interesting.

Jorge Russo

ICREA, University of Barcelona

Effects of D-instantons in string amplitudes

In type IIB superstring theory, D-instanton contributions to some physical quantities can be incorporated by generalizing tree-level results by a proper SL(2,Z) symmetrization. This approach has led to the determination of the exact non-perturbative form of certain terms in the type IIB effective action. We consider an SL(2,Z) symmetric version of the four-graviton amplitude and factorize the pure D-instanton contribution. We find some surprising effects in the different energy regimes. These results show that non-perturbative effects can lead to a high-energy behavior which is significantly different from the perturbative string behavior.

Alberto Santambrogio

Physics Dept. - Theory Division - Universita' degli Studi di Milano - Bicocca

On higher spins (Ref.: hep-th/0405069, 0410090, 0210114)

Roberto Emparan

ICREA, University of Barcelona

Black Rings

I will give an overview of work done in the last few years on a novel class of black holes in five dimensions with ring-shaped horizons. In particular, I will discuss their implications for black hole uniqueness, as well as their role within string theory.

Alberto Lerda

Universita' del Piemonte Orientale

Teorie di gauge e istantoni in background di stringa

Marco Caldarelli

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Giant Gravitons in AdS/CFT (Discussion on articles hep-th/0406096 and hep-th/0409174)

Matteo Cardella

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Non-supersymmetric strings vacua and quantum corrections to the classical moduli space

Discussion on Lin, Lunin, Maldacena's article (hep-th/0409174)

Mikhail Shifman

Theoretical Physics Insitute - Minnesota University

One flavor QCD from supersymmetric gluodynamics via planar equivalence

Alessio Celi

Leuven University

Fakeness of fake supergravity

Dario Melis

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Cosmological solutions of gauged maximal supergravities in three dimensions

Carlos Herdeiro

Physics Dept. - University of Porto

Recent Developmentes concerning Closed Timelike Curves in String Theory

Closed Timelike Curves are present in a number of solutions of Classical General Relativity and are, in general, regarded as pathological. It was suggested by Hawking in the early 90s that the `Chronology Protection Mechanism' should involve quantum effects. It becomes therefore interesting to explore the nature of CTC's in a framework of quantum gravity like string theory. The recent discovery of supersymmetric Godel type universes in string theory which are T-dual to pp-waves and the existence of supersymmetric rotating black holes (which have Closed Timelike Curves) possessing a CFT description motivated several suggestions on how string theory might cope with Closed Timelike Curves. In this seminar I will review some of these recent suggestions.

Dietmar Klemm

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Holographic interpretation of closed timelike curves

We give a pedagogical review of Goedel-type universes in string theory and of questions related to the appearance of closed timelike curves.

Pedro J. Silva

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Giant gravitons and CFT dual descriptions

Matteo Cardella

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Supersymmetry breaking from string orbifolds

Giovanni Ortenzi

Mathematics Dept. - Universita' degli Studi di Milano - Bicocca

On integrable systems

Matteo Boni

Physics Dept. - Theory Division - Universita' degli Studi di Milano

OPE and central charges in 4D SCFT

Stefano Maghini

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Spin chains and anomalous dimensions in N=4

Luca Martucci

Physics Dept. - Theory Division - Universita' degli Studi di Milano

On spinning strings and AdS/CFT

Sergio Cacciatori

Mathematics Dept. - Universita' degli Studi di Milano

On exact solutions in string theory

Pedro J. Silva

Physics Dept. - Theory Division - Universita' degli Studi di Milano

On giant gravitons

Leonardo Castellani

Universita' del Piemonte Orientale

Gauge theories on finite group spaces

La geometria differenziale dei gruppi finiti viene utilizzata per definire teorie di campo sulle corrispondenti \"varieta'\" discrete.

Alberto Cattaneo

Institut fuer Mathematik, Universitaet Zuerich

Branes in the Poisson sigma model and deformation quantization of constrained systems

The Poisson sigma model is a topological string theory with target a Poisson manifold (i.e., a manifold whose algebra of smooth functions is endowed with a Lie bracket that is also a derivation; e.g., a symplectic manifold). Particularly interesting is the case of open strings in genus zero (i.e., the worldsheet is a disk) as its perturbative functional integral quantization with \"free\" boundary conditions yields Kontsevich's formula for the deformation quantization of the target (i.e., an associative algebra structure on formal power series in Plank's constant of smooth functions such that the commutator yields the Poisson bracket in the classical limit). In this talk we address the problem of changing the boundary conditions (\"branes\"). It turns out that the possible branes are coisotropic submanifolds (the global version of Dirac's first class constraints, which appear when one has to do with systems with symmetry - from Lagrange's top to, in infinite dimensions, Yang-Mills theory). The functional integral quantization of the Poisson sigma model with branes yields interesting formulae including (when obstruction are absent) the deformation quantization of the reduced phase space of a given coisotropic submanifold.

Sergio Cacciatori

Mathematics Dept. - Universita' degli Studi di Milano

Comments on Ferrara, Sokatchev article \"Non-anticommutative N=2 super-Yang-Mills theory with singlet deformation\"

Marco Caldarelli

Physics Dept. - Theory Division - Universita' degli Studi di Milano

Supersymmetric solutions of N=2, D=4 gauged supergravity

We consider minimal gauged supergravity in four dimensions. After a short introduction to the main features of the theory, we construct all bosonic solutions admitting a Killing spinor. These solutions preserve generically one quarter of the supersymmetries, and fall in two classes, distinguished by the norm of the Killing vector constructed from the Killing spinor. If the Killing vector is timelike, the solutions are determined by the geometry of a two-dimensional base-manifold. When it is lightlike, the most general BPS solution is given by an electrovac AdS travelling wave. Finally, we generalize the classification to include external sources, and show that a particular solution describes a Goedel-type universe preserving one quarter of the supersymmetries.

Luis Alvarez-Gaume'

Theoretical Physics Division - CERN

Noncommutative Geometry in Physics

Since the development of Noncommutative Geometry, there have been some attempts to apply it in Physics. These attempts have been so far limited success, but many more possibilities remain open. We will present some aspects of these applications, and some prospects for the future.

Klaus Behrndt

Max Planck Institut fuer Gravitationsphysik, Albert Einstein Institut, Potsdam

Compactifications of type IIA and 11-d supergravity with fluxes

We consider compactifications of 11-d supergravity in the presence of fluxes and derive the constraints imposed by supersymmetry. The deformations on the geometry of the internal space are discussed. The compactification of type IIA supergravity appears as a special case.

Anastasios Petkou

Theoretical Physics Division - CERN

QCD meets strings

String theory was invented in the 70s to explain some phenomena in Strong Interactions, but quickly turned into a possible Theory of Everything. However, the recent discovery of AdS/CFT and the idea of Holography enabled String Theory to address basic questions regarding its starting point: Strong Interactions. After a review of the main ideas behind AdS/CFT and Holography, I discuss Semiclassical String configurations in Anti-de Sitter spacetimes and the new information they give for the anomalous dimensions, the glueball spectrum and the thermodynamics of Non-Abelian Gauge Theories.

Roman Jackiw

Center for Theoretical Physics - Department of Physics, MIT

Chern-Simons deformation of General Relativity

General relativity is extended by promoting the three-dimensional gravitational Chern-Simons term to four dimensions. This entails choosing an embedding coordinate v_\\mu -- an external quantity, which we fix to be a non-vanishing constant in its time component. The theory is identical to one in which the embedding coordinate is itself a dynamical variable, rather than a fixed, external quantity. Consequently diffeomorphism symmetry breaking is hidden in the modified theory: the Schwarzschild metric is a solution; gravitational waves possess two polarizations, each traveling at the velocity of light; a conserved energy-momentum (pseudo-) tensor can be constructed. The modification is visible in the intensity of gravitational radiation: the two polarizations of a gravity wave carry intensities that are suppressed/enchanced by the extension.

Jerome Gauntlett

Queen Mary - Physics Department, London

Classifying supergravity solutions

Supergravity solutions have played, and continue to play, an important role in string/M-theory. Most supergravity solutions have been constructed by guessing a suitable Ansatz, and so it is desirable to have a more systematic procedure. We will discuss a method which enables one to classify supergravity all solutions utilising the mathematical notion of G-structures.

Sergio Ferrara

Theoretical Physics Division - CERN

Forces, fundamental symmetries and basic constituents of the universe

An update is given on recent progress in the quest for a unified theory encompassing the fundamental interactions of particles and fields. New concepts, such as extended objects (branes) and duality, and older concepts such as renormalizability and supersymmetry, are merged in concepts such as renormalizability and supersymmetry, are merged in the search for a unitary scheme.