The Eurostrings 2022 conference will take place at Ecole Normale Supérieure in Lyon, from April 25 to April 29, 2022. It is part of a cycle of yearly conferences gathering researchers from all over Europe and elsewhere, working in the areas of quantum field theory, string theory, quantum gravity and related topics. The last in-person conferences in this cycle took place in 2018 in London, in 2017 in Milano and 2015 in Cambridge. After a long interruption due to the pandemic, we hope that this conference will be an opportunity for catching up through in-person discussions and fostering new collaborations.
Registration is now closed.
Review talks:
Invited talks:
Contributed talks:
International Advisory Committee:
TBA
I will present a powerful new method that for the first time allows us to compute the Kaluza-Klein spectrum of a large class of string theory compactifications. This includes geometries with little to no remaining (super-)symmetries, completely inaccessible by standard methods. I will discuss various applications of this method, including to the AdS/CFT correspondence and to the stability of non-supersymmetric AdS vacua. As I will show, some of these AdS vacua are unstable due to tachyonic Kaluza-Klein modes, while others are perturbatively stable.
I will discuss the large-N limit of the sphere partition function and the topologically twisted index of the ABJM theory and related SCFTs arising from M2-branes. Focusing on the subleading terms in the large-N expansion, I will study the implications of these results for black hole physics and holography.
Recent years have seen remarkable progress in our understanding of black holes: for black holes in AdS coupled to a bath, Page curves consistent with unitarity have been obtained through semi-classical computations involving quantum extremal surfaces. These computations are largely based either on two-dimensional models or on bottom-up braneworld models which may or may not make sense as consistent theories of quantum gravity. In this talk I will discuss top-down string theory constructions that realize black holes in four-dimensional theories of gravity coupled to a bath, and demonstrate that Page curves can be obtained in consistent theories of higher-dimensional gravity.
The AdS/CFT correspondence still has to throw clearer light on the dual (microscopic and fundamental) meaning of known violations of cosmic censorship: What mechanisms drive them? How do they manifest in the dual large-N field theory? How does the theory deal with them when N is finite and quantum gravitational bulk effects are incorporated? For this purpose, we study the evolution of the Gregory-Laflamme instability for black strings in global AdS spacetime, and investigate the CFT dual of the formation of a bulk naked singularity. We uncover a rich variety of dynamical behaviour -- including tsunami flows of horizon generators from the boundary, and nakedly singular horizon pinch-offs. The holographic dual describes different patterns of heat flow due to the Hawking radiation of two black holes placed at the antipodes of a spherical universe. We also present a model that describes the burst in the holographic stress-energy tensor when the signal from a bulk naked singularity reaches the boundary.
We will review recent constructions of AdS_3 and AdS_2 solutions with 4 supercharges for which the dual two dimensional and one dimensional conformal field theories have been identified as the IR fixed points of quiver-like field theories. These solutions describe the near horizon geometry of extremal black holes, so their dual CFTs can be used to compute their microscopical degrees of freedom. Moreover, we will show that some of these solutions can be interpreted as describing the backreaction of defect operators in conformal field theories of dimensions 4, 5 and 6.
Recent advances in the scattering amplitude-based approach to the Post-Minkowskian expansion of classical general relativity have demonstrated that this new approach holds the promise of significantly changing the efficiency of computations in general relativity. This approach completes the post-Newtonian computations by providing information beyond its regime of validity. This framework leads to surprising results connecting the conservative part and gravitational radiation effects. As well, the scattering amplitude methods apply to a wide range of effective field theories in various dimensions.
In this talk, we will present new results for the post-Minkowskian expansion in various dimensions. We will present a new organisation of the scattering amplitudes for an efficient evaluation of the classical post-Minkowskian contributions to high-loop order. We will discuss a reformulation of the effective-one-body formalism for connecting the scattering amplitudes to the effective classical hamiltonian of the two-body systems and gives applications to probe regime results and the high-energy limit in various dimensions.
The talk will explain the asymptotic structure of gravity in the asymptotically flat case by making central use of the Hamiltonian formalism. In particular, how the infinite-dimensional asymptotic symmetry group (BMS group) emerges at spatial infinity will be discussed. The case of electromagnetism will also be presented and extensions to supergravity will be addressed.
Nonrelativistic string theory is a corner of string theory with a nonrelativistic spectrum. The formulation on a flat target spacetime was introduced already twenty years ago, but recent progress in our understanding of non-Lorentzian geometries
such as Newton-Cartan geometry has enabled to formulate this sector on arbitrary curved nonrelativistic spacetimes. I will review these developments, and discuss
how strings on torsional string newton-cartan geometry arises from a limit of relativistic strings. I will also comment on a more general approach based on large speed of light expansions. Finally, I will discuss a further limit that leads to a novel class of worldsheet sigma models that not only have a non-relativistic target spacetime but also exhibit non-relativistic worldsheet symmetries, and show how such sigma models are connected to near BPS limits of the AdS/CFT correspondence.
An understanding of generalized global symmetries of a Quantum Field Theory (QFT) can provide deep insight into its strong coupling behavior. For example, spontaneous non-breaking of 1-form symmetry signals confinement. Standard tools for studying generalized global symmetries often rely on the existence of a Lagrangian description, and hence only apply to weakly coupled QFTs. However, all the known QFTs in five and six dimensions are inherently strongly coupled. In this talk, I will describe how the generalized global symmetries of 5d and 6d QFTs are encoded in their construction as a compactification of M/F-theory. I will not only discuss higher-form symmetries, but also higher-group structures mixing the higher-form symmetries.
Non-trivial K-theory groups and non-trivial cobordism groups can lead to global symmetries which are conjectured to be absent in quantum gravity. In this talk, a correspondence between the two groups is proposed. It is inspired by open-closed string duality and relies on a mathematical result known as Conner-Floyd isomorphism. As an application, it is shown how to recover known tadpole cancellation conditions of string theory from a purely bottom-up perspective. In the spirit of the swampland program, this can be used to give further support to the string lamppost principle.
In this talk I will describe recent advances on the study of the Higgs branch of rank-1 and rank-2 4d N=2 SCFTs. In particular, I will describe how one can obtain magnetic quivers for almost all these theories, which in turn allows to describe the Hasse diagram of the Higgs branch and sheds light on the the corresponding chiral ring. We also explore how SCFTs are connected by RG flows.
A proposal for the worldsheet string theory that is dual to free N=4 SYM in 4d is made. It is described by a free field sigma model on the twistor space of AdS5 x S5, and it exhibits a psu(2,2|4)_1 affine symmetry. The theory is a natural generalisation of the corresponding model for tensionless string theory on AdS3 x S3 whose description involves a free field realisation of psu(1,1|2)_1. I will explain how our proposal fits into the general framework of AdS/CFT, and review the various checks that have been performed.
I will briefly present the International Research Network on Quantum Fields and Strings, which was set up two years ago under the auspices of CNRS.
We study D-instanton contributions to supergravity scattering amplitudes beyond the leading order. These effects are non-perturbative in the string coupling, and are constrained by S-duality at low orders in the momentum expansion of the spacetime effective action. Our worldsheet approach reproduces the results expected from S-duality and also predicts infinitely many terms at higher orders in the momentum expansion.
The topological string free energy is given by an asymptotic series in the topological string coupling. I will first discuss how a finite difference equation can be derived from this asymptotic series for a class of Calabi-Yau backgrounds and how analytic solutions of these equations can be found. These solutions provide access to the non-perturbative structure and strong topological string coupling expansion. I will then discuss how the Borel transform can be obtained in these cases and how the Stokes jumps of the Borel transform contain the information of BPS invariants of the underlying Calabi-Yau geometry as well as their wall-crossing structure. I will furthermore discuss topological string S-duality in this context. This is based on own as well as joint work in collaboration with Iván Tulli, Jörg Teschner and Arpan Saha.
Euclidean D-branes wrapped on non-trivial cycles of a Calabi-Yau threefold are known to affect the metric on the hypermultiplet moduli space determining the effective action of type II strings on such manifolds. After reviewing the existing results on the instanton corrected metric following from a combination of constraints imposed by supersymmetry and dualities, I'll show how the D-instanton effects can be computed by a direct worldsheet approach. It required solving several conceptual and technical problems and can now be extended to compactifications with lower supersymmetry.
The talk is based on joint work with A. Sen and B. Stefanski.
While multicenter black holes in asymptotically flat space have long been object of study, the construction of multi black holes geometries in Anti-de Sitter spacetimes remains so far elusive. In this talk I will discuss recent progress on the search for these solutions. Working in the probe approximation, I will show that there exist stable ad metastable black hole bound states in compactifications of M-theory on 7-dimensional Sasaki-Einstein manifolds with Betti multiplets and AdS4 vacua. I will map out their thermodynamic landscape and discuss the relevance of these setups for describing glassy systems via holography. I will finally discuss their supersymmetric limits, in light of recent developments regarding the entropy matching for stationary AdS4 black holes via localization in the dual 3d CFT.
Following the recent work of Eberhardt, Gaberdiel and Gopakumar, exact comparison between various quantities living on the two sides of the AdS/CFT correspondence has become a possibility. The goal of this work is to extend the existing holographic dictionary to include some non-perturbative vacua on both sides. We start by constructing various D-branes of the string theory on ${\rm AdS}_3\times {\rm S}^3 \times \mathbb{T}^4$ at $k=1$ units of NS-NS flux and calculate their associated cylinder amplitudes. We observe that these amplitudes match with the cylinder correlators of certain boundary states of the dual CFT, thus suggesting a direct correspondence between these boundary conditions. We also show that the disk amplitudes of these D-branes localise to those points in the worldsheet moduli space where the worldsheet disk holomorphically covers the spacetime disk.
One of the major achievements of the study of integrability in AdS/CFT has been the development of the Quantum Spectral Curve (QSC): a powerful set of equations which give access to the full planar spectrum of N=4 SYM at finite coupling. These equations, which have the form of a nonlinear Riemann-Hilbert problem, are the central mathematical structure of integrability, and recent results indicate that they can be used to compute not only the spectrum, but also correlation functions.
A new version of the QSC was also found for the ABJM theory, but the generalization to integrable AdS3/CFT2 dual pairs remained an open problem. The main obstacle was the presence of massless modes in the integrable description of the worldsheet theory, which made it impossible to follow the usual derivation.
Recently, we proposed a Quantum Spectral Curve for string theory on AdS3xS3xT4 with pure Ramond-Ramond flux, using a new logic. The conjecture is based on symmetry principles and general properties of the QSC deduced from the AdS4 and AdS5 cases, and was shown to pass very nontrivial tests. Intriguingly, the new equations require to drop some of the assumptions on the solutions of the Riemann-Hilbert problem: the branch points are no longer of square-root type. This minimal modification was enough to rederive the highly complex dressing phases of the worldsheet S-matrix in the massive sector.
This proposal, if confirmed, opens the way to precision spectroscopy to reveal the properties of the still elusive dual CFT, for which there is no Lagrangian.
I will discuss in detail how we came to this conjecture, the evidence it is correct, and the many perspectives for the future. Based on 2109.05500, with N. Gromov, B. Stefanski and A. Torrielli.
to be specified later
The eigenstate thermalization hypothesis is one of the most universal features of chaotic quantum many-body systems, which claims that matrix elements of simple operators in high energy states has a universal structure which treats off-diagonal elements statistically. Along with the random-matrix like behaviour of energy eigenstates, it is one of the main smoking guns of quantum chaos. In this talk, I will introduce the OPE randomness hypothesis: a conjecture for the statistical distribution of OPE coefficients in chaotic conformal field theories. This hypothesis generalizes the ETH ansatz and treats OPE coefficients statistically, with a distribution given to leading order by a Gaussian distribution, with corrections exponentially suppressed in the entropy. I will give evidence for this conjecture, based on asymptotic formulas for OPE coefficients that can be derived thanks to crossing symmetry and for 2d CFTs, modular invariance. I will discuss the gravitational counterparts of these results and underline the importance of Euclidean wormholes.
This talk will start with an introduction to hydrodynamisation in an FRW universe. I first briefly describe the set-up and show how a hydrodynamic plasma dilutes and falls out of equilibrium due to expansion towards empty de Sitter spacetime [1]. Finally, I will show new technical advances that allowed us to dynamically evolve the boundary metric in accordance with the Friedmann equations [2]. Previously unphysical renormalisation constants now become physical parameters and depending on the boundary cosmological constant this leads to de Sitter, asymptotically flat or Big Crunch cosmologies.
[1] Jorge Casalderrey-Solana, Christian Ecker, David Mateos and WS, Strong-coupling dynamics and entanglement in de Sitter space, 2011.08194 (SciPost Phys)
[2] Christian Ecker, WS, David Mateos and Jorge Casalderrey-Solana, Holographic Evolution with Dynamical Boundary Gravity, 2109.10355
I will discuss recent new examples providing new links between quantum information, holography and quantum gravity: I will first introduce a refinement of the usual entanglement entropy for theories with global conserved charges, the so-called symmetry resolved entanglement entropy, and discuss its recent implementation in AdS3/CFT2 (2012.11274, 2108.09210). I will then elaborate on the use of geometric Berry phases to distinguish states with the same entanglement structure, such as the worm hole geometries dual to TFD states. Finally, I will report a recently-found reformulation of the large N limit of Nielsen complexity on the SU(N) manifold in terms of two-dimensional hydrodynamics.
