We discuss the presence of phonons and the interplay between spontaneous and explicit breaking of translations in the context of holography. Using two different bottom-up models we show the existence of transverse and longitudinal phonons, whose properties are in perfect agreement with elastic theory and hydrodynamics. We focus our attention on the elastic and transport features of the dual QFT also in the presence of a small explicit breaking. We conclude speculating about the possibility of having gravitational duals for strongly coupled viscoelastic materials.

I will present a new approach to study the RG flow in 3d N=4 gauge theories, based on an analysis of the Coulomb branch of vacua. The Coulomb branch is described as a complex algebraic variety and important information about the strongly coupled fixed points of the theory can be extracted from the study of its singularities. I will use this framework to study the fixed points of USp(2N) gauge theories with fundamental matter, revealing some surprising features at low amount of matter.

Superconformal field theories placed in nontrivial background fields for the metric and the continuous global symmetries exhibit a rich web of RG flows across dimensions. I will discuss several examples of such flows and emphasize some of their universal features. In addition, I will employ non-perturbative tools such as 't Hooft anomaly matching, a-, F-, and c-extremization, and holography to gain a quantitative understanding of some aspects of these theories. Finally, I will discuss the relevance of these results for a microscopic understanding of the entropy of supersymmetric black holes and strings in AdS.

From a modern viewpoint the "S-matrix bootstrap" is the idea that general consistency conditions can be used to obtain quantitative constraints on scattering amplitudes. I will discuss the assumptions behind this approach, open questions about the structure of amplitudes, and discuss some fundamental results from the sixties and seventies. In the second part of the talk I will treat two modern approaches which were inspired by recent results on the conformal bootstrap, and show how they can be used to constrain scattering amplitudes in non-trivial ways.

We describe the leading and sub-leading multi-soft behavior of tree level gluon amplitudes and an underlying two-dimensional description of such scenarios where the soft limits are currents related to asymptotic symmetries of YM theory. Such kinematic limits allow us to explore the algebra of these two dimensional currents and we comment on their CFT interpretation. Then we explore a possible two-dimensional description of certain amplitudes in massive scalar QFT’s.

I will discuss the computation of the graviton one-loop determinant in the BTZ black hole background with certain chiral boundary conditions at the AdS boundary. These boundary conditions were proposed by Compere, Song and Strominger and were shown to modify the asymptotic symmetry algebra from a sum of left and right Virasoro algebras to a single right-moving Virasoro U(1) Kac-Moody. This implies that the holographic dual description possesses such global symmetry and so should be described by a warped conformal field theory (WCFT) instead of a standard CFT. In the talk I will overview the new boundary conditions and the concept of a WCFT, outline the computational method of obtaining the one-loop determinant from the "quasinormal" mode spectrum (highlighting elements which are unique to the new boundary conditions) and discuss the implications of the results for the boundary field theory.

I will start with briefly describing the HISH ( Holography In- spired Hadronic String) model and reviewing the fits of the spectra of mesons, baryons, glueballs and exotic hadrons. I will present the determination of the hadron strong decay widths. The main decay mechanism is that of a string splitting into two strings. The corresponding total decay width behaves as Γ = πATL/2 where T and L are the tension and length of the string and A is a dimensionless universal constant. The partial width of a given decay mode is given by Γ_i/Γ = Φ_i exp(−2πCm^2_sep/T) where Φi is a phase space factor, msep is the mass of the ”quark” and ”antiquark” created at the splitting point, and C is a dimensionless coefficient close to unity. I will show the fits of the theoretical results to experimental data for mesons and baryons. I will examine both the linearity in L and the expo- nential suppression factor. The linearity was found to agree with the data well for mesons but less for baryons. The extracted coefficient for mesons A = 0.095 ± 0.015 is indeed quite universal. The exponential suppression was applied to both strong and radiative decays. I will discuss the relation with string fragmentation and jet formation. I will extract the quark-diquark structure of baryons from their decays. A stringy mechanism for Zweig sup- pressed decays of quarkonia will be proposed and will be shown to reproduce the decay width of Υ states. The dependence of the width on spin and flavor symmetry will be discussed. We further apply this model to the decays of glueballs and exotic hadrons.

The monodromy relations of scattering amplitudes in string theory provide an elegant formalism to understand some mysterious properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop-amplitudes in quantum field theory, but a loop-level generalisation of the stringy monodromy construction has been lacking for many years. In this talk I will first describe some of these recent developments in the domain of scattering amplitudes in gauge and gravity theories. I’ll then review the monodromies of open string worldsheets and how the lead at tree-level to deepening the understanding of the gauge theory perturbative expansion. Then I will describe in a non-technical manner our results and how we managed to extend these relations to all loops in string and field theory. I’ll finish by discussing implications for the loop expansion in general, and how to extend in principle these results to gravity. I will assume no prior knowledge of the audience in modern scattering amplitudes methods.

Models with spontaneously broken local supersymmetry are naturally obtained by coupling the off-shell supergravity-matter systems to Goldstino superfields. Every irreducible Goldstino superfield produces a universal positive contribution to the cosmological constant. This talk will review the structure of N=1 and N=2 Goldstino superfields.

In this talk I will discuss recent developments that have suggested new connections between the transport properties of strongly interacting matter and the field of quantum chaos. In particular I will describe how in many holographic theories there are simple relationships between the thermoelectric diffusion constants and the butterfly velocity, which describes the speed at which quantum chaos propagates.

TBA

I will discuss some aspects of the doubled geometry of double field theory. Double field theory provides a reformulation of supergravity with a manifest O(D,D) symmetry, which can be related to the T-duality invariance of string theory on a torus. I will review how one achieves this, by doubling the number of coordinates and introducing a generalised diffeomorphism symmetry. Then, I will discuss how one can characterise the properties of string theory backgrounds viewed as solutions of DFT, and in particular show how to derive the first law of black hole thermodynamics in this framework. Based mainly on 1507.07541 and 1608.04734 (with Alex Arvanitakis).

Compactifications of M-theory down to AdS4 are known to arise from Sasaki-Einstein internal spaces. The latter can be viewed as surfaces enclosing Calabi-Yau cone singularities, whose deformations can be described algebraically in a well established way. In this talk, I will present work in progress on describing deformations of the enclosing surfaces away from the Sasaki-Einstein metric, using the deformations of the Calabi-Yau cone. This provides a realisation of a class of SU(3) structure manifolds satisfying the conditions postulated in the standard treatments of M-theory compactifications on such manifolds. The result is a proposal for obtaining four dimensional N=2 supergravity models with gauged hypermultiplets from deformations of regular Sasaki-Einstein manifolds.

Recent work has uncovered relations between the rate at which chaotic behaviour spreads in strongly interacting quantum systems, and the diffusivities of certain processes in these systems. Focusing mainly on holographic examples, I will explore the extent to which these relations hold in states at non-zero density, where the diffusion of charge and energy are no longer independent processes.

A microstate geometry is a smooth, time-independent, asymptotically flat, horizon-free solution of type IIB supergravity. According to the “fuzzball" conjecture, such solutions describe individual microstates of black holes. Non-supersymmetric microstate geometries typically suffer from linearized instabilities. I will argue that supersymmetric microstate geometries suffer from a nonlinear instability. I will also discuss how such solutions lead to a new type of mathematical structure, so-called “ambipolar” hyperkahler manifolds, and explain how such manifolds can be constructed.

The appearance of integrability in the duality between the AdS5xS5 string and planar maximally supersymmetric Yang-Mills theory gives rise to many insightful results. Various deformations of this AdS/CFT dual pair are known to also be integrable, prompting the question how far the power of integrability extends in this setting. In recent years there has been a lot of progress in answering this question. Rather than trying to demonstrate integrability in known AdS/CFT dual pairs, efforts instead focused on finding manifestly integrability preserving deformations of the AdS5xS5 string. While constructed to preserve integrability, the resulting so-called Yang-Baxter sigma models are, however, not guaranteed to describe strings, or have an AdS/CFT interpretation. The former of these points has since been addressed and turns out to be closely related to (nonabelian) T duality, and we now understand which of these models continue to describe strings. The goal of my talk is to address the latter point, regarding the AdS/CFT interpretation of these models. I will use symmetry considerations to give a unified AdS/CFT picture for these Yang-Baxter strings as duals to various noncommutative deformations of supersymmetric Yang-Mills theory. My general conjecture matches many known dualities, and I will briefly discuss nontrivial tests in various new cases, in the form of brane constructions indicating the desired dualities.

The a-theorem expressing the monotonicity of renormalisation group flows in four (and other even) dimensions is now well-accepted. There is a function (the a-function) generating the RG beta-functions as a gradient flow via a positive-definite metric. However the standard definition of the a-function in terms of the trace anomaly of the energy-momentum tensor does not work in odd dimensions. In this talk we focus on the gradient-flow property of the a-function and show that a function with similar properties can be constructed order-by-order in three dimensions. We start by reviewing the a-function in even dimensions from a gradient-flow standpoint. Then we discuss our explicit calculations in three dimensions. Finally we present some progress towards relating our results to the F-function which has been shown to have the expected monotonicity properties at fixed points.

Recent advances in non-geometric string theory suggest that locally non-geometric flux compactifications can be understood in terms of nonassociative deformations of spacetime geometry. We will review some of these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory.