I present arguments that suggest that string theory should be viewed as an effective framework just like quantum field theory. The open/closed string and UV/IR correspondence indicate that gravity is emergent. I introduce the concept of entropic force and discuss it's subtleties. Next I present the case for the entropic origin of gravity and outline a route toward its derivation. Finally, I discuss some of the possible implications on this new view on gravity.

Effective Holographic Theories are employed in order to classify and study the critical dynamics at low temperature of quantum field theoritec systems in 2 and 3 spacial dimensions at finite charge density. The relevant dynamics variables involve the energy momentum tensor, a scalar relevant or marginal operator and the charge density current. A wealth of scaling phases are found with interesting and sometimes counterintuitive properties.

Strange metals are materials with numerous anomalous properties. The flow of electricity cannot be explained in the familiar language of a fluid of individual electrons, but instead requires a new strongly interacting description. In this talk, I will review some basic facts about these materials. With this as motivation, I will explain how to compute conductivity in certain strongly interacting, non-relativistic field theories which are defined holographically.

I will explain a gradient formula for beta functions of two-dimensional quantum field theories. The gradient formula has the form derivative c = - (gij+Delta gij+bij) bj where bj are the beta functions, c and gij are the Zamolodchikov c-function and metric, bij is an antisymmetric tensor introduced by H. Osborn and Delta gij is a certain metric correction. The formula is derived under the assumption of stress-energy conservation and certain conditions on the infrared behaviour the most significant of which is the condition that the large distance limit of the field theory does not exhibit spontaneously broken global conformal symmetry. Being specialized to non-linear sigma models this formula implies a one-to-one correspondence between renormalization group fixed points and critical points of c.

I will present the 1/2 BPS Wilson loop operator of N=6 super Chern- Simons-matter (ABJM theory) which is dual to the simplest macroscopic open string in AdS4 x CP3. The Wilson loop couples, in addition to the gauge and scalar fields of the theory, also to the fermions in the bi-fundamental representation of the U(N) x U(M) gauge group. These ingredients are naturally combined into a superconnection whose holonomy gives the Wilson loop, which can be defined for any representation of the supergroup U(NlM). Using the localization calculation of Kapustin et al. I will then show that the circular loop is computed by a supermatrix model and discuss the connection to pure Chern-Simons theory with supergroup U(NlM).

Recently there has been great interest in calculating transport coefficients for field theories at large coupling, using AdS/CFT. In this talk I will discuss recent work showing how to use the membrane paradigm to easily compute the shear viscosity and conductivity in arbitrary gravity theories. In a certain sense these can be thought of as effective couplings at the black hole horizon dual to the field theory plasma. An explicit Wald-like formula for these couplings is given for a large class of generalized gravity theories.

We discuss a couple of topics motivated by the Chern-Simons type gauge theory description of M2-branes in nontrivial backgrounds. In the first part we start by briefly reviewing the 3-algebra construction of Bagger, Lambert and Gustavsson. Then we propose an orbifold truncation prescription of 3-algebra, and show how one can 'derive' the ABJM model through matrix regularization. In the second part, we report on some explicit classical solutions of rotating membranes in Sasaki-Einstein 7-manifold M(111). We discuss the dual operators on the CS side, for several different class of spinning membranes.

Recently Kazakov, Vieira and the author conjectured the Y system set of equations describing the planar spectrum of AdS/CFT. In this paper we solve the Y system equations in the strong coupling scaling limit. We show that the quasiclassical spectrum of string moving inside AdS3 x S1 matches precisely with the prediction of the Y system. Thus the Y system, unlike the asymptotic Bethe ansatz, describes correctly the spectrum of one-loop string energies including all exponential finite size corrections. This gives a very non-trivial further support in favor of the conjecture. We also discuss how the generalization to the full AdS5 x S5 can be easily constructed using the PSU(2,2 4) symmetry of the problem.

Based on the results of 0906.4393 and 0910.5771, this talk will discuss the formulation of general 4D N=2 superconformal sigma-model in N=2 and N=1 superspace settings.

I will explain a gradient formula for beta functions of two-dimensional quantum field theories. The gradient formula has the form derivative c = - (gij+Delta gij+bij) bj where bj are the beta functions, c and gij are the Zamolodchikov c-function and metric, bij is an antisymmetric tensor introduced by H. Osborn and Delta gij is a certain metric correction. The formula is derived under the assumption of stress-energy conservation and certain conditions on the infrared behaviour the most significant of which is the condition that the large distance limit of the field theory does not exhibit spontaneously broken global conformal symmetry. Being specialized to non-linear sigma models this formula implies a one-to-one correspondence between renormalization group fixed points and critical points of c.

Freed-Witten anomaly is a global ambiguity of the string path integral measure in the presence of D-branes. It turns out it uniquely determines, by imposing its cancellation, the topological type of both the A and the B fields when restricted to the brane, as it naturally involves the interplay between open and closed string degrees of freedom. After introducing the suitable mathematical framework provided by the theory of gerbes with connections, I will try to characterize the nature of the gauge bundle on a brane in the most general closed string background. Furthermore, I will go over a case by case analysis, focusing on how it can account for fractional RR and Page charges and showing the physical relevance of the resulting K-theoretical improvement for classifying D-brane charges. Reference: L. Bonora, F. Ferrari Ruffino, R. S., arXiv: 0810.4291

The mini-superspace quantization of D=11 Supergravity is equivalent to the quantization of a E10-K(E10) coset space sigma model when the latter is restricted to the E10 Cartan subalgebra. As a consequence, the wavefunctions solving the relevant mini-superspace Wheeler-DeWitt equation involve automorphic (Maass wave) forms under the modular group W+(E10) cong PSL2(O). Using Dirichlet boundary conditions on the billiard domain a general inequality for the Laplace eigenvalues of these automorphic forms can be derived, which implies that the wave function of the universe is generically complex and always tends to zero when approaching the initial singularity. The potential significance of these properties for the question of singularity resolution in quantum cosmology is discussed, also in comparison with other approaches. The present approach offers interesting new perspectives on some long-standing issues in canonical quantum gravity.

The Romans mass is a discrete parameter in type IIA string theory. It is perhaps the most mysterious piece of the theory: for example, its non-perturbative, M-theoretic interpretation is still not known. In this talk, we will review recent efforts to understand it through another non-perturbative tool: holography. We will see how this parameter modifies the recent holographic interpretation of certain string vacua via Chern-Simons theories. This leads to certain field theory results that, in turn, help find new families of supersymmetric vacua of string theory with negative cosmological constant.

I will review the construction of BPS and non-BPS multicenter black hole solutions, and describe a class of smooth solutions that have the same charges and asymptotics as black holes, but do not have a horizon. I will then discuss some of the properties of these solutions and argue that they should correspond to typical microstates of extremal black holes. If so, string theory would imply that a classical extremal black hole solution is a thermodynamic approximation of an ensemble of horizonless configurations, and that this solution stops giving a valid description of the physics at the scale of the horizon. I will finish by discussing the extension of this to non-extremal black holes and its implications for the information paradox.

We give a method of deriving the field-strengths of all massless and massive, i.e. gauged, maximal supergravity theories in any dimension starting from the Kac-Moody algebra E11. Considering the subalgebra of E11 that acts on the fields in the non-linear realisation as a global symmetry, we show how this is promoted to a gauge symmetry enlarging the algebra by the inclusion of additional generators. Given the enlarged algebra corresponding to the massless theory, we show that this can be deformed to obtain the algebra corresponding to the gauged theory. We show how this works in detail for the case of Scherk-Schwarz reduction of IIB to nine dimensions. We then classify all the possible deformations in any dimensions and show that these are in one to one correspondence with all the possible gauged supergravities. This provides a very efficient, simple and unified derivation of the field strengths and gauge transformations of all the bosonic fields of any maximal supergravity theory.

I will discuss recent progress in understanding non-geometric string backgrounds. These are inherently stringy constructions that are globally well- defined only up to T-dualities. One approach in analyzing such backgrounds is through the corresponding effective gauged supergravities. The classification of the latter in terms of embedding tensors provides us with a picture of the landscape of such backgrounds, realized in terms of non-geometric fluxes. Also, it is by now evident that a doubling of the coordinates of the underlying geometry is necessary for describing these backgrounds, since their stringy nature implies that winding modes should be treated on equal footing with the momentum modes. This leads us to doubled geometries and in particular twisted doubled tori, that are expected to underlie general supergravity gaugings. Of particular interest is the worldsheet description of such doubled geometries which involves chiral boson models. Although these models are not Lorentz invariant in general, for the twisted doubled tori Lorentz invariance is restored. Furthermore, the conditions for conformal invariance of those models agree with the conditions from minimizing the corresponding supergravity potential. This result firmly establishes that chiral boson models with twisted doubled tori target spaces are the worldsheet theories underlying a very broad class of supergravity gaugings.

We study various matrix models as toy models of the gauge dual of the AdS spacetime and black hole. I will summarize what these matrix models teach us about the information paradox and emergence of the light speed limit.

I will present a phenomenological model of the quark-gluon plasma that stem from 5 dimensional holography. The model is superior to the previous 5D models as it incorporates the running of the gauge coupling. It is constructed by requirements from QCD and a few lattice data. I will describe the transport properties of the quark-gluon plasma such as the bulk viscosity, energy loss of heavy quarks etc and their effects on the observables.

We will discuss a direct prescription for computing the mixing among gauge invariant operators in N=4 SYM. This approach is based on the action of the superalgebra on the states of the theory and circumvents the problem of diagonalising the dilatation matrix. As an example, we will derive the leading and subleading planar quantum corrections to the BMN-like operators belonging to the supermultiplet with 2 impurities. Furthermore, we will discuss the relation to Beisert's SU(2,2) dynamic S-matrix approach. The same method can be applied in the BMN limit of the dual string description. The string theory expressions for the states match nicely the field theory ones up to order lambda'. We will also focus on the implications of the mixing terms for 3-point functions of 2 BPS and one non-BPS operator. Namely, should the mixing terms were not there, constraints following from the superconformal and the bonus U(1)Y symmetries would be violated. Subsequently, we will utilise the BMN limit of the AdS5xS5 string theory to analyse the string amplitudes corresponding to the 3-point functions studied above. The mixing is again crucial to ensure the cancellation of various amplitudes that would otherwise violate symmetry constaints. However,on the string side, we find examples of interactions which violate expectations coming from superconformal Ward identities and the U(1)Y symmetry. Finally, we will comment on the possible resolution of this mismatch.