Eurostrings 2024

2 Sept 2024, 08:00 → 6 Sept 2024, 18:00 Europe/London

University of Southampton

Parallel Sessions Parallel Sessions overview.pdf

Monday 2 September

08:00 → 09:00 Registration

09:00 → 09:15 Welcome

09:00 Welcome remarks

09:15 → 10:15 Review talk

Convener: [Chair: Kostas Skenderis]

09:15 The dual of semi-classical gravity

Recent work has produced a consistent picture of the holographic dual description of semi-classical gravity. I will describe this picture, several applications of this picture including the factorization puzzle and the information paradox, and some open questions.

Speaker: Jan de Boer (Nikhef National institute for subatomic physics (NL))

southampton0924.pdf

10:15 → 11:00 Coffee break

11:00 → 12:30 Plenary session

Convener: [Chair: Antoine Van Proeyen]

11:00 Complexity and bulk momentum

I will discuss the conjectured relation between the bulk momentum and the rate of growth of complexity in CFTs from the perspective of the recent developments on complexity in the Krylov basis.

Speaker: Paweł Caputa (University of Warsaw)

EuroStrings2024PC.pdf

11:30 Smooth generalized symmetries

I describe an axiomatic formulation of QFT (following Segal, Atiyah, and Kontsevich) using bordism and the language of infinity categories. In this language, QFTs are collectively assembled into a generalized space, whose (higher) homotopy groups encode (generalized) symmetries of QFTs. In this picture, 't Hooft anomalies can be understood as a failure to respect locality. A new kind of anomaly arises, which can be understood as a failure to respect smoothness; an example occurs already in the quantum mechanics of a two-state system.

Speaker: Ben Gripaios

eurostrings_annot_gripaios.pdf

12:00 Modularity and Resurgence for N=4 Integrated Correlators

I will describe a surprisingly simple representation of a class of integrated correlation functions of four superconformal primaries in the stress tensor multiplet of $\mathcal{N}=4$ supersymmetric Yang-Mills theory with arbitrary simple gauge group, $G$. I then present exact formulae for these integrated correlators which are manifestly invariant under GNO electro-magnetic duality. For classical gauge groups, $G=SU(N), SO(N), USp(2N)$, in the large-$N$ limit these correlators are interpreted via holography in terms of the low-energy expansion of type IIB superstring amplitudes in $AdS_5\times S^5$ or an orientifold thereof.
From the asymptotic perturbative large-$N$ expansion of these integrated correlators we can reconstruct non-perturbative, but modular invariant exponentially suppressed terms via resurgence analysis.

Speaker: Daniele Dorigoni (Durham University)

talkDD.pdf

12:30 → 14:00 Lunch break

14:00 → 15:30 Parallel sessions: Black holes

Convener: [Convener: Alejandra Castro]

14:00 The light we can see: Extracting black holes from weak Jacobi forms

Modular forms play a pivotal role in the counting of black hole microstates. The underlying modular symmetry of counting formulae was key in the precise match between the Bekenstein-Hawking entropy of supersymmetric black holes and Cardy's formula for the asymptotic growth of states. The goal of this talk is to revisit the connection between modular forms and black hole entropy, and tie it with other consistency conditions of AdS/CFT. We will focus our attention on weak Jacobi forms. I will quantify how constraints on polar states affect the asymptotic growth of non-polar states in weak Jacobi forms. The constraints I'll consider are sparseness conditions on the Fourier coefficients of these forms, which are necessary to interpret them as gravitational path integrals. In short, the constraints will leave an imprint on the subleading corrections to the asymptotic growth of heavy states. With this we will revisit the UV/IR connection that relates black hole microstate counting to modular forms. In particular, I’ll provide a microscopic interpretation of the logarithmic corrections to the entropy of supersymmetric black holes and tie it to consistency conditions in AdS_3/CFT_2.

Speaker: Alejandra Castro

EuroStrings-2024.pdf

14:30 Isospectrality in Effective Field Theory Extensions of General Relativity

Two universal predictions of general relativity are the propagation of gravitational waves of large momentum along null geodesics and the isospectrality of quasinormal modes in many families of black holes. In extensions of general relativity, these properties are typically lost: quasinormal modes are no longer isospectral and gravitational wave propagation is no longer geodesic and it exhibits birefringence — polarization-dependent speed. We study these effects in an effective-field-theory extension of general relativity with up to eight-derivative terms and show that there is a unique Lagrangian that has a non-birefringent dispersion relation for gravitational waves and isospectral quasinormal modes in the eikonal limit. We argue that both properties are related through a generalized correspondence between eikonal quasinormal modes and unstable photon-sphere orbits. These properties define a special class of theories that we denote as isospectral effective field theories. We note that the lowest-order isospectral correction to general relativity coincides with the quartic-curvature correction arising from type II string theory, suggesting that isospectrality might be a key feature of quantum gravity.

Speaker: Marina David

Isospectrality_Short_MD.pdf

14:50 Null infinity as an inverted extremal black hole horizon

It was recently remarked that the hypersurface of null infinity of asymptotically flat spacetimes is a non-expanding horizon. We utilize this observation and propose a duality between the asymptotic structure of asymptotically flat spacetimes and the near-horizon structure of extremal black holes. The link between these two classes of geometries comes in the form of spatial inversions that conformally map one onto the other. An explicit manifestation of this duality is the four-dimensional extremal Reissner-Nordström geometry, which has the special property of being self-dual under the mapping, better known in the literature as the Couch-Torrence inversion. The existence of the Couch-Torrence inversion then provides matching conditions between near-horizon and near-null-infinity modes of perturbations of the extremal Reissner-Nordström black hole. We demonstrate that a direct consequence of this is the identification between an infinite tower of near-horizon (Aretakis) and near-null-infinity (Newman-Penrose) conserved charges.

Speaker: Panagiotis Charalambous (SISSA)

02_09_2024_Eurostrings2024.pdf

15:10 AdS_3 Black Holes Double Copy from Mini-Twistor space

In flat space, it is well understood how to obtain gravity by "squaring" gauge theories through the double copy. This holds for scattering amplitudes and classical solutions (in coordinate and twistor space). In the past few years, it was realized that the Penrose transform explains the existence of a classical double copy and that this realization can be extended to 3d spacetimes for wave solutions. In this talk, I will show a novel curved space double copy construction. By using cohomology class representatives in Mini-Tiwistor space, I will show that the double copy also holds for 3d warped black holes that are solutions of Topologically Massive Gravity. This requires a setup where the black holes are viewed as exact perturbations around AdS_3 with length L=3/m (m=mass of graviton). Finally, I will show a byproduct of this formalism that allows the construction of a double copy for boost eigenstates that arise in Celestial Holography.

Speaker: Mariana Carrillo Gonzalez (Imperial College London)

Ads3DCshort.pdf

Ads3DCshort.pptx

14:00 → 15:30 Parallel sessions: Bootstrap I

Convener: [Convener: Balt Van Rees]

14:00 Constraining Glueball Couplings

We set up a numerical S-matrix bootstrap problem to rigorously constrain bound state couplings given by the residues of poles in elastic amplitudes. We extract upper bounds on these couplings that follow purely from unitarity, crossing symmetry, and the Roy equations within their proven domain of validity. First we consider amplitudes with a single spin 0 or spin 2 bound state, both with or without a self-coupling. Subsequently we investigate amplitudes with the spectrum of bound states corresponding to the estimated glueball masses of pure SU(3) Yang-Mills. In the latter case the 'glue-hedron', the space of allowed couplings, provides a first-principles constraint for future lattice estimates.

Speaker: Balt van Rees

Eurostrings Southampton 2.pdf

14:30 CFT Data of Stringy Operators of N = 4 Super-Yang-Mills at Strong Coupling

We consider 4d N=4 SYM theory in the planar limit at strong coupling. We focus on “stringy” operators which are single-trace operators accessible by integrability (for example by the Quantum Spectral Curve). We discuss how to assign stringy operators to KK-towers on AdS5 \times S5 and how the degeneracy of excited strings breaks.

We use these observations to lift the degeneracy of the structure constants of the “stringy” operators at the leading order at strong coupling unmixing the existing constrains. We describe the observed patterns of the Structure Constants as well as possible insights on string interactions they can provide us.

The talk is based on 2310.06041.

Speaker: Nika Sokolova

Eurostrings 2024.pdf

14:50 Trace anomalies and graviton-dilaton scattering amplitudes

I will describe how various vertices and scattering amplitudes, involving background fields, probe trace anomaly coefficients in a four-dimensional (4D) renormalization group (RG) flow. Specifically, I will explain how to couple dilaton and graviton fields to the degrees of freedom of 4D QFT, ensuring the conservation of the Weyl anomaly along the RG flow for the coupled system. By providing dynamics to the dilaton and graviton fields, I will demonstrate that the graviton-dilaton scattering amplitude receives a universal contribution, exhibiting helicity flipping and being proportional to ($\Delta c-\Delta a$) along any RG flow. Here, $\Delta c$ and $\Delta a$ represent the differences in the UV and IR CFT $c$- and $a$-trace anomalies, respectively. Using a dispersion relation, ($\Delta c-\Delta a$) can be related to spinning massive states in the spectrum of the QFT. We test our proposal through various perturbative examples including free theories and weakly relevant flows. Finally, as an application of the proposal of probing the trace anomalies using scattering amplitude, we have derived a non-perturbative bound on the UV CFT $a$-anomaly coefficient using numerical S-matrix bootstrap program for massive RG flow.

Speaker: Mr Biswajit Sahoo (King's College London)

Eurostrings_Biswajit_Sahoo.pdf

15:10 Field theory expansions of string theory amplitudes

Motivated by quantum field theory (QFT) considerations, we present new representations of the Euler-Beta function and tree-level string theory amplitudes using a new two-channel, local, crossing symmetric dispersion relation. Unlike standard series representations, the new ones are analytic everywhere except at the poles, sum over poles in all channels and include contact interactions, in the spirit of QFT. This enables us to consider mass-level truncation, which preserves all the features of the original amplitudes. By starting with such expansions for generalized Euler-Beta functions and demanding QFT like features, we single out the open superstring amplitude. We demonstrate the difficulty in deforming away from the string amplitude and show that a class of such deformations can be potentially interesting when there is level truncation. Our considerations also lead to new QFT-inspired, parametric representations of the Zeta function and π, which show fast convergence.

Speaker: Dr Arnab Priya Saha (Indian Institute of Science)

String_amp_CSDR.pdf

14:00 → 15:30 Parallel sessions: Holography (applied) I

Convener: [Convener: Aristomenis Donos]

14:00 Nearly critical superfluids and holography

I will discuss the low energy dynamics of finite temperature systems which are close to a superfluid phase transition. In the regime, the amplitude of the order parameter needs to be included in the description captured by the hydrodynamics of conserved quantities and the Goldstone mode. After presenting a field theoretic construction of a suitable effective theory, I will examine the phenomenology of suitable holographic systems.

Speaker: Aristomenis Donos (Durham University)

Donos.pdf

14:30 Fluid/Gravity Duality for Viscoelastic Crystals

The hydrodynamics of crystals without topological defects (e.g. dislocations) can be accounted for by considering a set of 2-form global symmetries. In thermal equilibrium, the holographic dual to such a crystal is an AdS black brane charged under 2-form gauge fields. By extending the fluid-gravity correspondence to such backgrounds we obtain both dissipative and non-dissipative transport coefficients. We also consider the spectrum of hydrodynamical modes and find instabilities for a certain range of our theory’s parameters.

Speaker: Andre Oliveira Pinheiro (Heriot-Watt University)

AndrePinheiro_Southampton.pdf

14:50 On the GCL prescription for Schwinger-Keldysh holography

The complete description of non-equilibrium quantum dynamics necessitates the use of the so-called doubled Schwinger-Keldysh contour in complex time. Recently, Glorioso, Crossley and Liu proposed a convienent prescription for obtaining such SK effective actions from holography, by considering a specific contour in the complex bulk radial plane.
In this work we show how the GCL prescription can be derived from the Skenderis-van Rees prescription for real-time holography, which instructs us to fill in the boundary path integral contour with (generally complex) manifolds. We also comment on the applicability of the GCL prescription in near-equilibrium, hydrodynamic settings.

Speaker: Vaios Ziogas (Bristol University)

Eurostrings24_Ziogas.pdf

15:10 Black hole pseudospectrum in AdS

We investigate the stability of the spectrum of (scalar, vector and gravitational) quasinormal modes of electrically charged black branes in asymptotically AdS5 spacetimes under small perturbations of the theory. To achieve this, we formulate the problem as a generalised eigenvalue problem in ingoing Eddington–Finkelstein coordinates, which is advantageous in terms of numerical convergence. Our analysis reveals an increasing spectral instability with higher overtone numbers, consistent with observations in asymptotically flat spacetimes. Additionally, we provide evidence for pseudo-resonances as well as transient instabilities, which can potentially trigger nonlinear instabilities. Finally, we show that the asymptotic behaviour of pseudospectral contour lines is universal across perturbations and is best fit as a polynomial in the real part of the frequency, in contrast to the logarithmic behaviour in asymptotically flat spacetimes.

Speaker: Christiana Pantelidou (University College Dublin)

Pantelidou.pdf

14:00 → 15:30 Parallel sessions: QFT I

14:00 Non-Invertible Surface Defects in 3d QFTs from Half Spacetime Gauging

Non-invertible symmetries in general spacetime dimensions have attracted many attentions recently. I will present novel results for duality defects in 2+1 dimensional theories with $\mathbb{Z}^{(0)}_N\times\mathbb{Z}^{(1)}_N$ global symmetry and trivial mixed 't Hooft anomaly. By gauging these symmetries simultaneously in half of the spacetime, duality defects can be constructed for theories that are self-dual under gauging. The fusion rules involving duality defects form a fusion 2-category. I will also construct the corresponding symmetry topological field theory, a four-dimensional BF theory on a slab which realizes the duality defect on the boundary upon shrinking the interval. Furthermore, I will provide explicit examples of such duality defects in $U(1)\times U(1)$ gauge theories, in more general product theories and in non-Lagrangian theories obtained by compactification of 6d $\mathcal{N}=(2,0)$ SCFTs of type $A_{N-1}$ on various three-manifolds. Finally, I will discuss constraints on trivially gapped phases due to the existence of duality defects and a generalization of the above construction in five dimensions.

Speaker: Lorenzo Ruggeri (Tsinghua University)

Eurostrings2024.pdf

14:30 The free energy of the large-N fermionic Chern–Simons theory in the ‘temporal’ gauge on R2 and S2

Most of the computational evidence for the Bose–Fermi duality of fundamental fields coupled to $U(N)$ Chern–Simons theories originates in the large-N calculations performed in the light-cone gauge. In this paper, we use another gauge, the ‘temporal’ gauge,
to evaluate the finite temperature partition function of $U(N)$ coupled regular and critical fermions on $\mathbb{R}^2$ at large $N$. We first set up the finite temperature gap equations, and then
use tricks we invented like 'symmetrization' to solve these equations exactly and evaluate the partition function. Our final results are in perfect agreement with earlier light-cone gauge results. The success of our ‘temporal’ gauge calculation potentially opens a path to computations that are awkward in light-cone gauge but more natural in the ‘temporal’ gauge, e.g. the evaluation of the thermal free energy on a finite-sized sphere.

Speaker: Mr Souparna Nath (Tata Institute of Fundamental Research)

Fermionic_Chern_Simons_theory_on_S_2_S_1.pdf

14:50 Higgsing SCFTs via Decay and Fission of Magnetic Quivers

We explore supersymmetric QFTs with eight supercharges. At superconformal fixed points, these theories typically lack a Lagrangian description, complicating their study. Recently, the magnetic quiver has been proposed as a tool to encode the Higgs branches of these theories. Utilizing this tool, our recent papers [1,2] propose a new algorithm: Decay and Fission of Magnetic Quivers, which performs Higgs branch RG-flows (Higgsings) on superconformal field theories (SCFTs). The power of the algorithm lies in its inherent simplicity, and I will show its application to SCFTs in dimensions d=3, 4, 5, and 6, including 4d Class S theories, Argyres-Douglas theories, 5d SQCD theories at UV fixed points, 6d orbi-instantons and higher-rank E-string. Furthermore, I will discuss the algorithm as a tool for studying the geometry of the Higgs branch as a symplectic singularity, demonstrating its advantages over previous algorithms, and providing evidence for the existence of a new isolated symplectic singularity.

[[1]] Phys. Rev. Lett. 132, 221603
[[2]] [2401.08757]

Speaker: zhenghao zhong

Zhenghao Zhong Eurostrings 2024.pdf

15:10 Superconformal indices in N=(0,2) Quantum Mechanics

Conformal symmetry introduces two predominant complications into one dimensional sigma models by constraining the target space geometry to a cone. Namely, the naive spectrum of the corresponding quantum mechanics suffers from the noncompactness and singularity issues, thus rendering the Witten index an ill-defined object. We demonstrate how these challenges can be overcome by introducing a refined superconformal index, computed through localization for a general class of N=(0,2) models. These models are expected to play a significant role in a top-down understanding of AdS(2)/CFT(1) duality. More concretely, we will discuss an application for the Coulomb branch of the quiver mechanics which describes the bound states of D-branes.

Speaker: Canberk Sanli (CEICO, FZU Prague)

eurostrings_talk_24.pdf

14:00 → 15:30 Parallel sessions: Resurgence & non-perturbative methods I

Convener: [Convener: Daniele Dorigoni]

14:00 Resurgence in CFT2 - Minimal models and beyond?

Following the example of previous work by Benjamin et al. and Kaplan et al., we look at the large charge expansion of the identity block in CFT2. The motivation is clear in AdS/CFT: to look for black holes in the graviton expansion! We start by exhausting the resurgence analysis of four-point function of the (2,1) degenerate fields at finite cross-ratio z. We see that Stokes phenomena in the asymptotic series in large c are controlled by the cross-ratio z, and that the Stokes jumps reveal the other block in the OPE. Time permitting, I'll discuss future directions and on going explorations.

Speaker: Tomás Reis (SISSA)

eurostrings-talk.pdf

14:30 Integrated correlators in a $SU(N)$ $\mathcal{N}=2$ SYM theory with fundamental flavours

I will discuss recent developments in the study of integrated 4-point correlators of primary operators in a four-dimensional $\mathcal{N}=2$ superconformal field theory with $SU(N)$ gauge group and matter in the fundamental and anti-symmetric representations. Exploiting supersymmetric localization, it is possible to map the computation of these correlators to an interacting matrix model and obtain expressions that are valid for any value of the ’t Hooft coupling in the large-$N$ limit of the theory, allowing to explore subleading orders in the planar expansion, too. In particular, I will focus on the strong-coupling regime, showing how to extract analytically the strong-coupling expansion of the integrated correlators from these exact expressions.

Speaker: Paolo Vallarino

Eurostrings_PV.pdf

14:50 Brane scattering from integrated correlators in N=4 SYM

Integrated correlators in N=4 SYM represent a powerful tool to obtain exact results in the coupling constant, and can be used as constraints for dual string scattering amplitudes in AdS. In this talk we study special classes of integrated correlators, dual to scattering processes in presence of extended branes in the bulk. First, we consider 4pt correlators with determinant operators, which in the planar limit are heavy operators realizing a giant graviton D3-brane in the dual space. Secondly, we discuss correlators with line defects such as Wilson/'t Hooft loops, dual to extended (p,q)-strings in the bulk under SL(2,Z) transformations. We compute their integrated correlator via supersymmetric localization exactly in the 't Hooft coupling, interpreting such results as worldsheet integrated amplitudes in presence of boundaries.

Speaker: Francesco Galvagno (Queen Mary University of London)

Eurostrings.pdf

15:10 On the structure of wave functions in complex Chern-Simons theory [cancelled]

In this talk, I will present recent work on the structure of wave functions in complex Chern-Simons theory on the complement of a hyperbolic knot in the three-sphere. The holomorphic blocks in the decomposition of the full non-perturbative wave function conjecturally possess a hidden integrality structure that guarantees the cancellation of potential singularities at rational points. The exact wave function in the rational case is expressed in closed form in terms of the new integer invariants. Alternatively, it is computed by solving recursively the q-difference equation encoded in the quantum A-polynomial of the knot. Finally, I will illustrate our conjectural statements in the benchmark example of the figure-eight knot. This talk is based on arXiv:2312.00624 (joint work with M. Mariño).

Speaker: Ms Claudia Rella (University of Geneva)

slides_rella_02092024.pdf

15:30 → 16:15 Coffee break

16:15 → 17:45 Plenary session

Convener: [Chair: Marika Taylor]

16:15 Classical Observables from the Exponential Representation of the Gravitational S-Matrix

We present a streamlined approach to evaluating classical observables in gravitational two-body scattering using the exponential representation of the scattering matrix. This method leverages the KMOC description of observables, where the classical contribution boils down to a simple matrix element of an operator. In the conservative sector, this operator corresponds to the radial action. We will further demonstrate how this framework, combined with the velocity cut formalism, allows for efficient calculation of classical observables within the post-Minkowskian expansion.

Speaker: Pierre Vanhove (Institut de Physique Théorique - CEA/Saclay)

eurostrings-2024.pdf

16:45 ABJM theory and defect RG flows

I will talk about defect renormalization group flows recently found in ABJM theory. In such a setting, we find RG flow trajectories that may or may not preserve some subset of the original N=6 supersymmetry. The beta-functions have a large spectrum of fixed points representing superconformal defects that provide a rich arena to study quantum effects in 2+1 dimensional theories. This sheds new light on universal information about ABJM, such as the Bremsstrahlung function, and possibly on the holographic dual setting of strings in AdS4xCP3.

Speaker: Marcia Tenser (Università Milano-Bicocca)

Eurostrings_2024_Presentation_v2-1.pdf

17:15 Aspects of Gauge-Strings Duality

I will discuss some recent progress in the duality between gauge fields and string, in particular in what respects recent advances on models of confinement.

Speaker: Carlos Nunez (Swansea University)

carlosforEurostrings2024final.pdf

18:00 → 19:30 Reception

Tuesday 3 September

09:00 → 10:00 Review talk

Convener: [Chair: Diego Trancanelli]

09:00 Review talk on Holography in asymptotically flat spacetime

Speaker: Laura Donnay (SISSA)

EuroStrings_2024_Review.pdf

10:00 → 10:30 Plenary session

Convener: [Chair: Diego Trancanelli]

10:00 Carrollian Amplitudes from the Flat Limit of AdS Witten Diagrams

Carrollian holography aims to express gravity in four-dimensional asymptotically flat spacetime in terms of a dual three-dimensional Carrollian CFT living at null infinity. Carrollian amplitudes are massless scattering amplitudes written in position space which can be re-interpreted as correlators in a putative dual Carrollian CFT. I will review the properties of these amplitudes and argue that they are the natural objects obtained in the flat limit of boundary correlators in AdS computed via Witten diagrams. I will show that the flat limit in the bulk of AdS implies a Carrollian limit in the boundary CFT. The flat limit procedure is entirely taken in position space using Bondi coordinates in the bulk, which allows to keep track of the Carrollian limit taking place at the boundary. Notably, the kinematic constraints on the AdS correlators, such as the bulk-point singularity, emerge naturally in the Carrollian limit and do not have to be imposed a priori.

Speaker: Romain Ruzziconi (University of Oxford)

SLIDES.pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Plenary session

Convener: [Chair: Simon Ross]

11:00 Gravitational Waves from the Fifth Dimension

The experimental revolution unleashed by the discovery of gravitational waves will gradually unfold over the coming decades. Maximizing the discovery potential requires a theoretical understanding of out-out-of-equilibrium quantum matter coupled to dynamical classical gravity. I will discuss the insights that holography can offer into this challenging regime. I will focus on phase transitions in the early Universe and in neutron star mergers. If time permits I will also discuss the holographic dual of primordial black hole formation.

Speaker: David Julian Mateos Solé (ICREA & UB)

11:30 Exploring thermal CFTs

In this talk, I will present recent developments in the study of Conformal Field Theories (CFTs) at finite temperature. Thermal dynamics are constrained by the Kubo-Martin-Schwinger (KMS) condition. I will present novel sum rules for one-point functions, providing a basis for setting up a numerical bootstrap problem. The KMS condition can also be used to extract the leading behaviour of one-point functions for heavy operators analytically. What is more, I will extend the thermal bootstrap approach to temporal line defects, akin to Polyakov loops in gauge theories. The power of this framework will be demonstrated with specific examples.

Speaker: Elli Pomoni (DESY)

Eurostrings (2).pdf

12:00 Holographic correlators with multi-particle states

In the AdS/CFT context, 1/2-BPS asymptotically AdS supergravity solutions
can be used to derive holographic 4-point correlators. Beside reproducing
known strong-coupling results for the 4-point correlators with single
particle states, this approach can be used to derive new 4-point
correlators with two single particle and two multiparticle states. I will
provide some explicit examples of these correlators with double-particle
states both in AdS3 and AdS5. The results can be written in terms of a
natural generalisation of the usual D-functions appearing in the 4-point
correlators with single particle states.

Speaker: Rodolfo Russo

rodolfo_russo.pdf

12:30 → 14:00 Lunch break

14:00 → 15:30 Parallel sessions: Bootstrap II

Convener: [Convener: Shai Chester]

14:00 Bootstrapping string and M-theory

We combine supersymmetric localization with the numerical conformal bootstrap to non-perturbatively study 4d N=4 super-Yang-Mills (SYM) and 3d ABJM theory for all N and coupling, which is dual to string theory and M-theory, respectively. For N=4 SYM, are bound on the lowest dimension operator interpolates between weak coupling results for the Konishi operator, and strong coupling results for the lowest double trace operator, including the first few stringy corrections. For ABJM, are bounds match strong coupling results from M-theory, and we are also sensitive to higher trace operators. In both cases, are results suggest that bootstrap + localization is sufficient to numerically solve holographic theories non-perturbatively, opening a new window on strongly coupled quantum gravity.

Speaker: Shai Chester (imperial college london)

EuroStrings.pdf

14:30 Matrix Quantum Mechanics bootstrap at finite temperature

Matrix QM bootstrap is a method which utilizes the equations of motion together with norm positivity to allow for a numerical determination of moments to high precision. I will cover the general pronciples and some of the recent advances. Particularly, I will explain how to extend the bootstrap to finite temperature and present comparisons to analytic methods.

Speaker: Barak Gabai (EPFL)

MQMBoot.pdf

14:50 Bootstrapping frustrated magnets: the fate of the chiral ${\rm O}(N)\times {\rm O}(2)$ universality class

We study multiscalar theories with $\text{O}(N) \times \text{O}(2)$ symmetry. These models have a stable fixed point in $d$ dimensions if $N$ is greater than some critical value $N_c(d)$. The expectation is that at this critical value $N_c(d)$ a merger between the stable and unstable fixed point occurs and that for $N < N_c(d)$ the fixed points move off into the complex plane. Previous estimates of this critical value from perturbative and non-perturbative renormalization group methods have produced mutually incompatible results. We use numerical conformal bootstrap methods to constrain $N_c(d)$ for $3 \leq d < 4$. Our results show that $N_c > 3.78$ for $d = 3$. This favors the scenario that the models that are physically relevant to the description of frustrated magnets where $N = 2,3$ and $d=3$, do not have a stable fixed point, indicating a first-order transition. We also find evidence for the merger-and-annihilation scenario being responsible for the disappearance of this fixed point in the form of the square root behavior of $\Delta_{SS}$ as $N_c$ is approached from above. Our result highlights the utility of modern algorithms for the numerical conformal bootstrap.

Speaker: Marten Reehorst

Slides_EuroString_2024_FrustratedMagnets.pdf

15:10 Bootstrapping the AdS Veneziano amplitude

I will present the derivation of the AdS Veneziano amplitude for the scattering of gluons in type IIB string theory on AdS5×S5/Z2​ in the presence of D7 branes, in a small curvature expansion. This is achieved by combining a dispersion relation in the dual 4d N=2 SCFT with an ansatz for the amplitude as an open string worldsheet integral over single-valued polylogarithmic functions evaluated on the real line. Single-valued functions arise because curvature corrections can be thought of as extra insertions of soft gravitons. In this way we fix the first two curvature corrections, which satisfy consistency checks in the high energy limit, the low energy expansion as previously fixed using supersymmetric localisation, and for the classical energy of the exchanged massive string operators. Our result predicts new Wilson coefficients and quantum corrections to the energies of massive strings that could be checked with future localisation, semi-classical or integrability computations.

Speaker: Tobias Hansen (Durham University)

hansen_eurostrings24.pdf

14:00 → 15:30 Parallel sessions: Holograhy (flat) I

Convener: [Convener: Tim Adamo]

14:00 Celestial chiral algebras in higher dimensions

In four spacetime dimensions, the self-dual sectors of gauge theory and gravity have infinite-dimensional chiral symmetry algebras which live on the Riemann sphere. These play a crucial role in the celestial holography programme, enabling the bootstrap of all-order collinear expansions and underpinning the only known top-down constructions for asymptotically flat holography. In higher dimensions, it has been unclear how or if these chiral algebras generalise, though. I will describe how chiral algebras can be defined for certain subsectors of gauge theory and gravity when the spacetime dimension is an integer multiple of four. Remarkably, the resulting algebras are still defined on the Riemann sphere, raising some interesting questions about how celestial holography could be implemented in higher-dimensions.

Speaker: Tim Adamo

Adamo_ES24.pdf

14:30 Lessons from light-cone formulation for physics at null infinity

Considering the simple case of 2D massless scalar fields in the light-cone formulation, we shall explore several subtleties that arise when setting up the canonical formulation on a single or on two intersecting null hyperplanes. Our analysis is particularly well-suited for a consistent treatment of zero modes, matching conditions (akin to the antipodal map for asymptotic symmetries), and infinite-dimensional global and conformal symmetries. We shall also comment on some aspects of the light-cone formulation that are relevant to Carrollian field theories, which have garnered attention in recent years in the context of flat-space holography. This talk is based on Arxiv:2401.14873 and some ongoing works.

Speaker: Sucheta Majumdar (Centre de Physique Théorique, Marseille)

Eurostrings_Majumdar.pdf

14:50 w(1+infinity) Algebra with a Cosmological Constant and the Celestial Sphere

It is shown that there exists a simple deformed version of Strominger’s infinite-dimensional w(1+infinity) algebra of soft graviton symmetries, which we conjecture to arise in spacetimes with a nonvanishing cosmological constant. The deformed algebra contains a subalgebra generating SO(1,4) or SO(2,3) symmetry groups of dS4 or AdS4, depending on the sign of the cosmological constant. The transformation properties of soft gauge symmetry currents under the deformed w(1+infinity) are also discussed.

Speaker: Dr Bin Zhu (University of Edinburgh)

Eurostrings24_Bin_Zhu.pdf

15:10 Operator product expansion in carrollian CFT

I will present new progress in constructing a general operator product expansion for carrollian CFTs, and discuss its realization within carrollian correlation functions dual to massless scattering amplitudes. The establishment of a carrollian OPE is crucial to a bootstrap formulation of carrollian conformal field theory in general, and would appear primordial at a conceptual level as well as for developing predictive tools that do not rely on previously known amplitudes.

Speaker: Mr Kevin Nguyen (Université Libre de Bruxelles)

KevinNguyen_talk.pdf

14:00 → 15:30 Parallel sessions: Holography (applied) II

Convener: [Convener: Michal Heller]

14:00 Holographic timelike entanglement entropy: prescription and application

Holographic entanglement entropy has significantly advanced our understanding of the emergence of spacetime and paved a way for other sharp geometric proxies of the bulk such as holographic complexity. In the course of the past two years, it was proposed that a promising complementary proxy of the bulk, sensitive in particular to the emergence of the bulk time, is given by an analytic continuation of the (holographic) entanglement entropy to timelike separated boundary subregions. In my talk I will discuss the bulk prescription for computing this timelike entanglement entropy based on intrinsically complex extremal surfaces and present its applications to black hole spacetimes, in particular as a probe of black hole singularity and as a new way of quantifying entanglement production in quenches.

Speaker: Michal P. Heller (Ghent University)

michal_heller-eurostrings-2024.pdf

14:30 The dynamics of first-order phase transitions in holographic theories

First-order phase transitions are somewhat neglected by theorists in favor of their second-order counterparts. Yet they contain rich physics, and are of importance in everything from condensed matter physics to (perhaps) early-universe cosmology.

I will discuss the dynamics of first-order transitions at strong coupling, using holographic duality. First, I describe how to construct effective actions which can be used to compute all quasi-equilibrium parameters relevant for bubble nucleation. Second, I discuss computations of the terminal velocity of expanding bubbles. Lastly, I focus on the case where bubble nucleation is suppressed, allowing the system to reach the edge of metastability, the spinodal point. Spinodals harbor critical phenomena akin to those of second order transitions, including diverging relaxation times which disrupt adiabatic evolution. I explain how this is realized in a simple holographic setup.

Speaker: Oscar Henriksson (Åbo Akademi University)

Eurostrings 2024 Southampton Henriksson.pdf

Eurostrings 2024 Southampton Henriksson.pptx

14:50 Carroll Gravity, BKL Dynamics and Holography

While Carroll geometry has exciting applications in the context of flat space holography, we can also consider ultra-local Carroll limits in gravity itself. At first, this may seem like an esoteric thing to do, compared to for example the non-relativistic expansion of gravity. However, Carroll limits in GR turn out to give remarkable simplifications. In this talk, I will connect these limits to BKL limits of gravity, which similarly describe similarly solvable yet rich chaotic dynamics in the vicinity of singularities. These limits have recently reappeared in the context of AdS/CFT, and I will reproduce some of those models from matter-coupled Carroll gravity. Finally, I will discuss some ongoing work on how Carroll limits of gravity can be used to go beyond existing near-singularity limits.

Speaker: Gerben Oling (University of Edinburgh)

oling-eurostrings-2024.pdf

15:10 Black Hole Singularity from OPE

Eternal asymptotically AdS black holes are dual to thermofield double states in the boundary CFT. It has long been known that black hole singularities have certain signatures in boundary thermal two-point functions related to null geodesics bouncing off the singularities (bouncing geodesics). In this talk I will discuss the manifestations of black hole singularities in the dual CFT.

By decomposing the boundary CFT correlator of scalar operators using the Operator Product Expansion (OPE) and focusing on the contributions from the identity, the stress tensor, and its products, I will show that this part of the correlator develops singularities precisely at the points that are connected by bulk bouncing geodesics. Black hole singularities are thus encoded in the analytic behavior of the boundary correlators determined by multiple stress tensor exchanges. Furthermore, I will show that in the limit where the conformal dimension of the operators is large, the sum of multi-stress-tensor contributions develops a branch point singularity as predicted by the geodesic analysis. I will then argue that the appearance of complexified geodesics, which play an important role in computing the full correlator, is related to the contributions of the double-trace operators in the boundary CFT.

Speaker: Nejc Čeplak (Trinity College Dublin)

CeplakNejcEurostringsv4.pdf

CeplakNejcEurostringsv5.pdf

14:00 → 15:30 Parallel sessions: Supergravity I

Convener: [Convener: Dario Martelli]

14:00 Localization in Supergravity

Equivariant localization is a powerful method for performing integrals using fixed point theorems.
Recently it has been applied to compute various holographic observables in supergravity without the need for solving any of the supergravity field equations.
In particular the on-shell action takes a prticularly simple form depending only on topological data.
I will discuss applications of these techniques in various setups.

Speaker: Alice Luscher (University of Oxford)

Eurostring_Slides (1).pdf

14:30 Wilson Loops and Spherical Branes

In this talk, I will focus on the study of 1/2-BPS Wilson loop operators in maximally supersymmetric Yang Mills theories on (p+1)-dimensional spheres. The gravity duals to these theories are given by the backreacted geometry of spherical Dp-branes and our aim is to compute the holographic Wilson loops in these backgrounds up to next-to-leading order in the large ’t Hooft coupling expansion. This is achieved by evaluating the partition function of a probe fundamental string in these backgrounds up to one loop order, from the string theory perspective, and by comparing this to the vacuum expectation value of the supersymmetric Wilson loop from the field theory side.

Speaker: Alexia Nix (University of Iceland)

Eurostrings2024_AlexiaNix.pdf

14:50 Exploring thermal black holes in a precise AdS_5/CFT_4 setup

Starting from 1810.11442 it was discovered that the dominant supersymmetric Euclidean AdS_5 black hole saddle is non-extremal (but complex, thus avoiding no-go theorems). If extremality is further imposed it becomes the standard supersymmetric and extremal (real) BPS saddle. At leading order in large N the thermodynamics of this saddle is recovered holographically by computing the superconformal index of the dual 4d field theory.

I will describe a novel limit towards the vicinity of the BPS point, characterized by two independent parameters: small physical temperature (T) and a small deviation from supersymmetry (ε). In the near-horizon limit the supergravity saddle becomes an exact solution to the equations of motion, further it solves the Killing spinor equation to first order in ε, and to all orders in T. I will then discuss the thermodynamic properties of this near-extremal, near-horizon limit and derive its super-Schwarzian mode. Depending of progress, I will also discuss how the super-Schwarzian mode is encoded holographically, and how, despite the supersymmetry breaking, one can still retain calculational control in the dual field theory to first order in ε.

If time permits, I will also relate this discussion to recent ongoing work on odd-dimensional equivariant localization in supergravity.

Speaker: Vasil Radoslavov Dimitrov (Unito Torino)

slides.pdf

15:10 Exotic Spheres, Kaluza-Klein Formalism and Supergravity

Exotic spheres are seven-dimensional, compact manifolds, which have been shown (through a non-constructive existence theorem) to admit numerous Sasaki-Einstein metrics. Hence, they are suitable candidates for compactifications of M-theory, but have never been considered in this context due to the lack of a suitable description. In this talk, I will discuss metrics on exotic spheres viewed as non-principal S^3 bundles over S^4, i.e. Milnor's bundles, summarising what was found in arXiv:2309.01703 (J. High Energ. Phys. 2023, 100 for the published version) and some ongoing work with David Berman and Martin Cederwall. I will outline the importance of these manifolds in differential geometry, and then present in detail an explicit Kaluza-Klein metric for one of the exotic spheres. I will discuss its properties, in terms of geometric quantities and physical energy conditions, then comment on its relation to 7-dimensional Euclidean gravity and its role in supergravity theories. Finally, I will discuss some interesting extensions of this work, which lies within a little-explored, but potentially fruitful, territory.

Speaker: Tancredi Schettini Gherardini (Queen Mary University of London)

Presentation - Tancredi Schettini Gherardini.pdf

14:00 → 15:30 Parallel sessions: Symmetries

14:00 On classical integrability of heterotic strings

A novel classically integrable model is proposed. It is a deformation of the two-dimensional principal chiral model, embedded into a heterotic σ-model. This is inspired by the bosonic part of the heterotic σ-model and its recent Hamiltonian formulation of the heterotic σ-model in terms of O(d,d+n)-generalised geometry. Classical integrability is shown by construction of a Lax pair and a classical R-matrix. Latter is almost of the canonical form with twist function and solves the classical Yang-Baxter equation.

Speaker: David Osten (University of Wroclaw)

Heterotic Integrability Eurostrings David Osten.pdf

14:30 Categorical-Symmetry Resolved Entanglement in CFT

We propose a symmetry-resolved entanglement for categorical non-invertible generalized symmetries (CaT-SREE) in (1+1)-dimensional CFTs. The definition parallels that of group-like invertible symmetries employing the concept of symmetric boundary states with respect to a categorical symmetry. Our examination extends to rational CFTs, where the behavior of CaT-SREE mirrors that of group-like invertible symmetries. This includes instances of the breakdown of entanglement equipartition at the next-to-leading order in the cutoff expansion. The findings shed light on the interplay between categorical symmetries, entanglement, and boundary conditions in (1 + 1)-dimensional CFTs.

Speaker: Arpit Das

Eurostrings24_AD.pdf

14:50 W-symmetries, anomalies and heterotic backgrounds with SU holonomy

It has been known that 2-dimensional supersymmetric sigma models admit symmetries generated by covariantly constant forms. For target spaces manifolds $M^n$ whose holonomy is included in $U(\frac{n}{2})$, $SU(\frac{n}{2})$, $Sp(\frac{n}{4})$, $Sp(\frac{n}{4}) \cdot Sp(1)$, $G_2 (n=7)$ and Spin(7)$(n=8)$, these symmetries close as a W-algebra. In heterotic sigma models, these symmetries are anomalous due to the presence of chiral worldsheet fermions in the action and must be cancelled to preserve the geometric interpretation of the theory.

In this talk, I will consider sigma models with target spaces (10-dimensional) supersymmetric heterotic backgrounds with $SU(2)$ and $SU(3)$ holonomy. I will present the W-algebra generated by the covariantly constant forms of the theory, pointing out that it closes under the inclusion of additional generators which are identified. Requiring the chiral anomalies to satisfy the Wess-Zumino consistency conditions at one-loop in perturbation theory, I will provide their explicit expressions. Finally, I will discuss the cancellation of the anomalies at the same loop level either by adding suitable finite local counterterms in the sigma model effective action or by assuming a plausible quantum correction to the transformations.

Based on arXiv:2305.19793 with G. Papadopoulos and E. Perez-Bolanos.

Speaker: Mr Loukas Grimanellis (King's College London)

Eurostrings 2024.pdf

15:10 The Harry Dym hierarchy and AdS_3 General Relativity

The novel connection between the asymptotic dynamics of 2+1 General Relativity with Integrable Systems has been studied recently due the possibility to explore holography beyond conformal symmetry. In this regard, we construct a set of suitable boundary conditions for the gravitational field which deforms those of Brown-Henneaux using negative powers of the central charge. Through a recursive method , we construct a novel infinite tower of conserved charges in involution under Poisson bracket. The boundary dynamics corresponds to the equations belonging to the Harry Dym hierarchy. For the simplest case, the theory admits black hole solutions such as the BTZ black hole.

Speaker: Francisco Reyes (Universidad de Santiago de Chile)

Harry Dym Eurostrings 2024.pdf

15:30 → 16:00 Coffee break

16:00 → 17:30 Plenary session

Convener: [Chair: David Vegh]

16:00 Tuning Ramond-Ramond flux for AdS3 strings

Studying strings on backgrounds with RR fluxes quantitatively is very challenging. A perfect arena to make progress is that of AdS3 geometries, where one may start from better-understood NSNS backgrounds and gently switch on RR fluxes.

I will review the recent (and not-so-recent) progress in this direction, obtained by a combination of integrability, worldsheet CFT and dual CFT techniques at various points of the moduli space, including at two distinct "tensionless" points.

Speaker: Alessandro Sfondrini (University of Padova)

sfondrini.pdf

16:30 Algebraically special holography

I will discuss algebraically special solutions of four-dimensional gravity in the context of holography. These are exact solutions of the field equations that contain a number of arbitrary transverse functions subject to non-linear constraints. In the case of negative cosmological constant, the configuration space defined by such solutions is not compatible with standard Dirichlet boundary conditions, resulting in a modified holographic dictionary. I will discuss the variational problem for algebraically special solutions, its holographic interpretation, and its connection with the thermodynamics of accelerating AdS black holes.

Speaker: Ioannis Papadimitriou (National and Kapodistrian University of Athens (GR))

2024.09.03 - eurostrings.pdf

17:00 A new index for a new black hole

In 2012.08530 a supersymmetric black hole with spindle horizon was constructed, displaying some striking new features and opening up at least two lines of investigations. Firstly, prompted by the new black hole in the past three years several new supergravity solutions based on orbifolds have been constructed in the literature. Moreover, via holography, these results motivated the study of supersymmetric field theories defined on orbifolds. This program was initiated in 2303.14199, where a new index, unifiying and generalising the superconformal and topologically twisted indices, was introduced and named the spindle index. The recent paper 2404.07173 analyses the large N limit of the spindle index thus deriving the microstates of a very general class of supersymmetric, rotating and accelerating black holes. This completes the costruction of the first example of a holographic duality involving supersymmetric field theories defined on orbifolds with conical singularities.

Speaker: Dario Martelli (Università di Torino and INFN Torino)

Eurotrings2024_seminar.pdf

Wednesday 4 September

09:00 → 10:00 Review talk

Convener: [Chair: Silvia Penati]

09:00 Cosmological correlators: symmetries, singularities, synergies

This talk will review some of the background and recent developments in cosmological correlators. We discuss the role of symmetries, and singular kinematic limits revealing a surprising connection to flat-space scattering amplitudes. These connections have inspired new approaches based on amplitudes ideas including the cosmological bootstrap. At the same time, the action of bulk de Sitter isometries as boundary conformal transformations makes natural the use of ideas from conformal field theory and holography.

Speaker: Paul McFadden

Eurostrings_McFadden.pdf

10:00 → 10:30 Plenary session

Convener: [Chair: Silvia Penati]

10:00 Towards de Sitter holography from quantum information

TBD

Speaker: Shira Chapman (Ben Gurion University)

ShiraChapman_Eurostrings.pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Parallel sessions: Amplitudes

Convener: [Convener: Oliver Schlotterer]

11:00 Integration on higher-genus Riemann surfaces from and for string amplitudes

In this talk, multiloop string amplitudes are discussed as a rewarding laboratory to develop integration techniques on higher-genus Riemann surfaces. I will review a string-amplitude inspired generalization of the Brown-Levin elliptic polylogarithms and their Kronecker-Eisenstein integration kernels to arbitrary genus. The key ingredients are convolutions of Arakelov Green functions on genus-g surfaces which transform as tensors under the modular group Sp(2g, Z). Our higher-genus integration kernels simplify the spin-structure summations in the RNS formulation of multiloop string amplitudes and the low-energy expansion of moduli-space integrals. The recent Fay identities among the higher-genus kernels play a key role in the development of more general integration algorithms relevant to precision calculations for particle colliders or gravitational-wave experiments and to mathematical classifications of period integrals on higher-genus surfaces.

Speaker: Oliver Schlotterer (Uppsala University)

Eurostrings_OS.pdf

11:30 Non-planar integrated correlator in $\mathcal{N}=4$ SYM

Integrated correlator of four superconformal stress-tensor primaries in $SU(N)$ $\mathcal{N}=4$ super Yang-Mills (SYM) theory in the perturbative limit takes a remarkably simple form, where the $L$-loop coefficient is given by a rational multiple of $\zeta(2L+1)$. In this talk, we extend the previous analysis of expressing the perturbative integrated correlator as a linear combination of periods of $f$-graphs, graphical representations for loop integrands, to the non-planar sector at four loops. At this loop order, multiple zeta values make their first appearance when evaluating periods of non-planar $f$-graphs, but cancel non-trivially in the weighted sum. The remaining single zeta value, along with the rational number prefactor, makes a perfect agreement with the prediction from supersymmmetric localisation.

Speaker: Shun-qing Zhang

eurost_zhang.pdf

11:50 A double copy from twisted (co)homology at genus one

We study the twisted (co)homology of a family of genus-one integrals — the so called Riemann-Wirtinger integrals. These integrals are closely related to one-loop string amplitudes in chiral splitting where one leaves the loop-momentum, modulus and all but one puncture un-integrated. While not actual one-loop string integrals, they share many properties and are simple enough that the associated twisted (co)homologies have been completely characterized. We use the intersection index — an inner product on the vector space of allowed contours — to derive a double-copy formula for the closed-string analogues of Riemann-Wirtinger integrals (one-dimensional integrals over the torus). These intersection indices form a genus-one KLT-like kernel defining bilinears in meromorphic Riemann-Wirtinger integrals that are equal to their complex counterparts.

Speaker: Andrzej Pokraka

Genus1DC.pdf

12:10 Non-analytic terms of string amplitudes from partial waves

Despite recent progress in the evaluation of 4pt string amplitudes, not much is known about the coefficients in their low energy expansion beyond genus 1. I will describe a simple method, based on the partial-wave decomposition of the tree-level amplitude, which predicts the leading logarithmic discontinuity at any order in \alpha' and any genus. Based on WIP with Yu-tin Huang and Michele Santagata.

Speaker: Mr Hynek Paul (KU Leuven)

Eurostrings_Hynek_Paul.pdf

11:00 → 12:30 Parallel sessions: Black holes and quantum information

Convener: [Convener: Julian Sonner]

11:00 Chaos, Complexity and Black Holes

Speaker: Julian Sonner (Universite de Geneve (CH))

EurostringsSonner.pdf

11:30 Entanglement Entropy via replica trick and theories with islands in higher dimensional curved backgrounds.

Entanglement entropy quantifies the degree of entanglement between two quantum systems or between two subregions in a QFT and hence is an important tool to understand the quantum system. Certain tricks (Replica) and holographic duals (Ryu-Takayanagi Area) have been used to calculate this measure. However, its study in dimensions > 2 has been mostly limited to flat backgrounds and CFT vacuum states in specific subregions due to technical as well as conceptual difficulties. I will present our work trying to bridge this gap, by calculating the EE for a CFT state in a subregion in higher dimensional curved backgrounds using the replica trick. In the presence of gravity, the quantum corrections to the black hole entropy is crucial in resolving the information paradox. Recently, its study in 2 dimensions led to the island proposal as a potential correction required to preserve unitarity in black hole evaporation. We will use our result for EE in higher dimensional black hole background, to discuss if islands exist in higher dimensions (d > 2) and obtain constraints on the QFT spectrum for islands to exist.

Speaker: Arvind Shekar (University of Southampton)

Arvind_Eurostrings slides.pdf

11:50 On the Backreaction of Dirac Matter in JT Gravity and SYK Model

We model backreaction in AdS$_2$ JT gravity via a proposed boundary dual Sachdev-Ye-Kitaev quantum dot coupled to Dirac fermion matter and study it from the perspective of quantum entanglement and chaos. The boundary effective action accounts for the backreaction through a linear coupling of the Dirac fermions to the Gaussian-random two-body Majorana interaction term in the low-energy limit. We calculate the time evolution of the entanglement entropy between graviton and Dirac fermion fields for a separable initial state and find that it initially increases and then saturates to a finite value. Moreover, in the limit of a large number of fermions, we find a maximally entangled state between the Majorana and Dirac fields in the saturation region, implying a transition of the von Neumann algebra of observables from type I to type II. This transition in turn indicates a loss of information in the holographically dual emergent spacetime. We corroborate these observations with a detailed numerical computation of the averaged nearest-neighbor gap ratio of the boundary spectrum and provide a useful complement to quantum entanglement studies of holography.

Speaker: Chen-Te Ma (Iowa State University)

20 mins.pdf

12:10 Bulk quantum corrections for non-spatial holographic entanglement

We introduce a generalized entanglement entropy, known as entwinement, in 2d CFTs measuring entanglement between non-spatially organized degrees of freedom. Its holographic dual is at leading order given by the area of codimension two surfaces winding around black hole horizons or naked singularities. We study bulk quantum corrections to this formula, generalizing results by Faulkner, Lewkowycz and Maldacena. Finally, we comment on implications for bulk geometry reconstruction from entanglement.

Speaker: Marius Gerbershagen

Eurostrings2024Gerbershagen.pdf

11:00 → 12:30 Parallel sessions: Cosmological bootstrap

Convener: [Convener: Massimo Taronna]

11:00 Holographic Correlators for all Lambdas

In this talk I will review recent efforts to put holographic correlators in maximally symmetric space-times on the same footings, upon analytic continuation to Euclidean AdS space. I will focus mainly on the dS example which played a key role for Cosmological Bootstrap. I will discuss in detail the analytic continuation introduced and how this continuation imply a map between perturbative expansion of in-in dS correlators and EAdS correlators, commenting also on their analyticity properties. Towards the end I will also close the circle mentioning some ongoing efforts to revisit celestial holography via hyperbolic EAdS and dS slicings.

Speaker: Massimo Taronna (University of Naples Federico II and INFN)

Eurostrings 2024 - Taronna.pdf

11:30 Hidden Simplicity of Cosmological Correlators

Cosmological observations suggest that the early universe was approximately described by a de Sitter geometry. In this background, the natural observables are in-in correlators, which can be computed by squaring the wavefunction of the Universe. Surprisingly, it turns out that in-in correlators are often much simpler than wavefunction coefficients and are closely related to scattering amplitudes in flat space. In this talk, I will make these statements more precise and describe new approaches which make the simplicity of in-in correlators manifest.

Speaker: ARTHUR,ELIAS LIPSTEIN (Durham University)

eurostrings_Lipstein.pdf

11:50 Cosmological Correlators From Flat Space Feynman Integrals

In this talk, I introduce a novel relationship between cosmological correlators and flat space Feynman diagrams in momentum space. Focusing on Witten diagrams in de Sitter space with heavy internal lines and light external legs, I introduce the Massive Flat Space (MFS) limit. In this limit, (i) the external energies entering the bulk-to-boundary propagators are sent to zero, (ii) the mass of the internal heavy lines is sent to infinity, while (iii) the product of the external energies and the mass remains fixed. Under these conditions, I derive a master equation that expresses the (off-shell) n-point correlator in the MFS limit as a contact diagram in de Sitter space, with a vertex factor corresponding to the amputated n-point graph in flat space. As a non-trivial application of this master equation, I provide analytical solutions to the one-loop bubble diagrams that contribute to inflationary correlators, in scenarios where the inflaton perturbations exhibit a reduced speed of sound.

Speaker: Sadra Jazayeri (Imperial College London)

Eurostring24 (1).pdf

12:10 [cancelled] Loops in (anti)de Sitter

After recalling the role of the topology of the de Sitter and anti de Sitter manifold in determining the main properties of Quantum Field Theories on such backgrounds, we will show how space configuration calculations allow to compute loop integrals in such maximally symmetric spacetimes. In particular, we will show how a remarkable Källén-Lehmann formula allows to compute banana integrals up to two loops on an (anti)de Sitter background.

Speaker: Sergio Luigi Cacciatori (Università degli Studi dell'Insubria, Department of Science and High Technology)

11:00 → 12:30 Parallel sessions: Holography (flat) II

11:00 Asymptotic symmetries and logarithmic soft theorems

In the last few years, a remarkable link has been established between the soft theorems and asymptotic symmetries of quantum field theories: soft theorems are Ward identities of the asymptotic symmetry generators. In particular, the tree-level subleading soft theorems are the Ward identities of the subleading asymptotic symmetries of the theory, for instance divergent gauge transformation in QED and superrotation in gravity. However, it is known that the subleading soft theorems receive quantum corrections with logarithmic dependence on the soft photon/graviton energy. It is therefore natural to ask how the quantum effects affect the classical (tree-level) symmetry interpretation. In this talk, we explore this question in the context of scalar QED and perturbative gravity. We show that the logarithmic soft theorems are the Ward identities of subleading asymptotic symmetries that arise from relaxed boundary conditions which take long-range interactions into account.

Speaker: Sangmin Choi (University of Amsterdam)

Sangmin Choi.pdf

11:30 Logarithmic soft graviton theorems from superrotation Ward identities

The study of infrared structure of gauge and gravity theories has gained renewed interest in recent years. This was possible after the seminal works of Strominger et al. unraveling relations between the so-called soft theorems and asymptotic symmetries. For the case of gravity theory, these relations also helped pave the way for celestial holography. In the last decade, these relations have been studied extensively and understood well at tree level. In this talk, I will present our work 2309.11220 where we extend this relation to one loop level. At this level, already for the soft theorem ambiguities appear. We resolve this ambiguity by noticing an equivalence between infrared corrections and newly found logarithmic corrections to soft theorems. We then present how the loop corrections can be related to the superrotation Ward identities thus confirming the relation at all orders in perturbation theory.

Speaker: Shreyansh Agrawal

Presentation_Eurostrings.pdf

11:50 Eikonal amplitudes on the celestial sphere

Celestial scattering amplitudes for massless particles are Mellin transforms of momentum-space scattering amplitudes with respect to the energies of the external particles, and behave as conformal correlators on the celestial sphere. However, there are few explicit cases of well-defined celestial amplitudes, particularly for gravitational theories: the mixing between low- and high-energy scales induced by the Mellin transform generically yields divergent integrals. In this talk, I will describe the results of a recent paper(in coll. with Tim Adamo, Wei Bu and Bin Zhu) where we argue that the most natural object to consider is the gravitational amplitude dressed by an oscillating phase arising from semi-classical effects known as eikonal exponentiation. This leads to gravitational celestial amplitudes which are analytic, apart from a set of poles at integer negative conformal dimensions, whose degree and residues we characterize. I'll also present the large conformal dimension limits, and provide an asymptotic series representation for these celestial eikonal amplitudes. Our investigation covered two different frameworks, related by eikonal exponentiation: 2→2 scattering of scalars in flat spacetime and 1→1 scattering of a probe scalar particle in a curved, stationary spacetime. These provide data which any putative celestial dual for Minkowski, shockwave or black hole spacetimes must reproduce. I'll finally comment on dispersion and monodromy relations that these celestial amplitudes obey and mention the Carrollian situation.

Speaker: Piotr Tourkine (CNRS, LAPTh, Annecy)

Eurostrings 2024 - Tourkine.pdf

12:10 Amplitudes and celestial OPEs around curved backgrounds

I will present the construction of tree-level amplitudes and chiral algebras around curved gauge theory backgrounds and space-times. Gluon two-point amplitudes around a self-dual dyon and graviton two-point amplitudes around self-dual Taub-NUT can be constructed by direct integration of the classical action. Twistor methods allow to extend the construction for MHV amplitudes at all multiplicity and these can be used to infer the celestial OPE around these backgrounds. More generally, I will outline the computation of the celestial chiral algebra around quaternionic Taub-NUT space-time, which includes AdS_4, Eguchi-Hanson, self-dual Taub-NUT and Burns space-times as particular cases.

Speaker: Giuseppe Bogna

eurostrings_slides.pdf

11:00 → 12:30 Parallel sessions: Swampland

Convener: [Convener: Miguel Montero]

11:00 Emergent geometry in string theory

Towers of light states are ubiquituous in string theory, either due to excitations of the fundamental string or Kaluza-Klein excitations of (dually) large internal spaces. Does this picture hold in non-geometric phases? Via worldsheet methods, I will present some recent results to the effect that it does.

Speaker: Ivano Basile (LMU)

Basile_Eurostrings_2024.pdf

11:30 Holography for KKLT: Anatomy of a Flow

Flux compactifications that give three- or four-dimensional Anti-de-Sitter vacua with a parametrically-small negative cosmological constant are supposed to be ubiquitous in String Theory. However, the 1+1 and 2+1 dimensional CFT duals to such vacua should have a very large central charges and rather unusual spectra. Furthermore, there are various swampland conjectures that such vacua should not exist. In this talk, I will explain how we construct brane configurations that source the would-be AdS vacua coming out of these flux compactifications, and identify certain UV AdS geometries that these systems of branes source. These place upper bounds on the possible values of the cosmological constants of the scale-separated AdS vacua.

Speaker: Yixuan Li (MPI Munich)

Eurostrings 2024 - Yixuan Li.pdf

11:50 S-folds: new N=4 D=4 consistent truncation of Type IIB and N=2 black-hole solutions

Exceptional Field Theory provides a natural framework to study compactification of 10/11D maximal supergravities. This tool allowed us to build new AdS$_4$ solutions by providing consistent truncations of Type IIB supergravity to $\mathcal{N}=8$ $D=4$ gauged supergravities. In this talk, we will review some AdS$_4 \times S^1 \times S^5$ solutions of Type IIB supergravity called “S-folds” as well as new $\mathcal N$=2 black-hole solutions with such asymptotic geometry. We will show how we can deform these solutions to obtain exactly marginal, stable, non-supersymmetric deformations, in tension with the non-susy AdS conjecture. Finally, we will present a new consistent truncation of Type IIB supergravity to pure $D=4$ $\mathcal{N}=4$ supergravity. This could be used to uplift several families of $D=4$ solutions in the existing literature, so far thought to originate only from a truncation of M-theory on $S^7$.

Speaker: Colin Yannick P Sterckx

Black-holes from type IIB S-folds.pdf

12:10 Dynamics and the Distance Conjecture

A cornerstone of the Swampland program is the Swampland Distance Conjecture (SDC), which postulates the appearance of (exponentially) light towers of states when approaching infinite distance points in moduli space. As such, the conjecture is formulated for adiabatic field displacements, corresponding to trajectories along a geodesic. However, realistic cosmological applications involve time-dependent field configurations and non-geodesic trajectories. In this talk, we will take some small steps towards a generalisation of the SDC to a dynamical setting.
To do so, we will study the cosmology of general, one-modulus asymptotic limits in String Theory, including the flux scalar potential for both the saxion and axion components. Borrowing tools from the theory of dynamical systems, we will be able to make some general statements about these asymptotic trajectories and their relation to the SDC.

Speaker: Filippo Revello (Utrecht University)

Revello_Eurostrings.pdf

12:30 → 14:00 Lunch break

14:00 → 17:00 Excursion: Winchester

18:00 → 22:00 Banquet: bar available from 6pm, seating at 6:30pm, dinner served at 7pm

Thursday 5 September

09:00 → 10:00 Review talk

Convener: [Chair: Nils Obers]

09:00 On recent developments in formal SQFT: a duality perspective

We will overview some of the recent progress in understanding supersymmetric QFT dynamics. Our discussion will be centered around different avatars of the notion of duality.

Speaker: Shlomo Razamat

Eurostrings2024B.pdf

10:00 → 10:30 Plenary session

Convener: [Chair: Nils Obers]

10:00 Elliptic Integrable Models and Their Spectra from Superconformal Indices

In this talk, I will review our recent progress in understanding the intricate relationship between elliptic finite-difference integrable models and 4D superconformal indices. Although this connection has been known for some time, we have recently achieved significant advancements in this area.

I will begin by briefly reviewing how these models arise in superconformal index computations, particularly when surface defects are introduced into 4D gauge theory. I will then discuss several such models that we have recently derived using these constructions. Finally, I will present our novel, physics-inspired approach to deriving the spectra of elliptic integrable models that have not been previously known. If time permits, I will also touch upon the relation of our construction to 5D ramified instantons.

This talk is based on a series of works in collaboration with Shlomo Razamat, Belal Nazzal, and Hee-Cheol Kim.

Speaker: Anton Nedelin (KCL)

eurostrings24_talk_extend.pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Plenary session

Convener: [Chair: Martin Ammon]

11:00 Replica wormholes and generalized Renyi entropies

The notion of generalized (von Neumann) entropy of entanglement plays a central role in the semiclassical island mechanism for information retrieval from black holes. In this talk, I will address the question whether there is a generalized Renyi entropy, for general replica number, within the context of gravity coupled to a radiation bath, by examining the nature of replica wormhole contributions in the simplified framework of JT gravity. I will show that the natural generalization, appearing in certain limits, is the generalized modular entropy whose extremization determines island saddle points for Renyi entropies with general replica number.

Speaker: Prem Kumar (Swansea University)

PK_Eurostringstalk.pdf

11:30 The DGKT scenario and the Weak Gravity Conjecture

I will discuss how generic quantum corrections lift the moduli space of BPS branes in 4d N=1 scale-separated solutions like DGKT. This means that there is a tension between this scenario and the WGC for membranes, which demands the existence of an exactly extremal brane.

Speaker: Miguel Montero (IFT UAM-CSIC)

eurostrings-24-montero.pdf

12:00 Asymptotics for subleading soft theorems at all orders

It is by now well understood how leading soft theorems follow as Ward identities of asymptotic symmetries defined at null infinity. For subleading infrared effects the connection is more subtle, but it turns out that this can be formalised, to all orders in the energy expansion, by adapting the Stuckelberg procedure to construct an extended radiative phase space at null infinity. I will exemplify this with Yang-Mills theory, showing the construction of the extended phase space, as well as the charges corresponding to the subleading soft theorems at all orders. These turn out to satisfy simple recursion relations, and organise themselves into infinite dimensional algebras in certain subsectors.

Speaker: Silvia Nagy

slides - v3.pdf

12:30 → 12:35 Conference photo

12:35 → 14:00 Lunch break

14:00 → 15:30 Parallel sessions: Cosmology (formal, string cosmology)

Convener: [Convener: Viktor Gorbenko]

14:00 Bra-Ket Wormholes in Cosmology

We study a model for the initial state of the universe based on a gravitational path integral that includes connected geometries which simultaneously produce bra and ket of the wave function. We argue that a natural object to describe this state is the Wigner distribution, which is a function on a classical phase space obtained by a certain integral transform of the density matrix. We work with Lorentzian de Sitter Jackiw-Teitelboim gravity in which we find semiclassical saddle-points for pure gravity, as well as when we include matter components such as a CFT and a classical inflaton field. In the regime of large universes our connected geometry dominates over the Hartle-Hawking saddle and gives a distribution that has a meaningful probabilistic interpretation for local observables.

Speaker: Viktor Gorbenko (EPFL - Ecole Polytechnique Federale Lausanne (CH))

Eurostrings 24.pdf

14:30 Constraints on inflation from the gravitational path integral?

A new axiom in QFT due to Kontsevich & Segal (https://arxiv.org/abs/2105.10161) which replaces the usual causality axiom by the requirement that the theory be well-defined on a special set of "allowable" complex metrics, has been suggested by Witten (https://arxiv.org/abs/2111.06514) to be elevated to a criterion in quantum gravity which distinguishes saddle points that could contribute to the semiclassical expansion of the gravitational path integral. In our recent (https://arxiv.org/abs/2305.15440) and ongoing work we explore this proposal in the context of the no-boundary wave function of the universe, finding among others that the criterion selects inflationary histories with a small tensor-to-scalar ratio in their CMB spectrum, in line with observations. This theoretical prior on observations in cosmology could give deep insights into the quantum state of the universe. The point of this talk is to summarize the above and explain what are the open questions.

Speaker: Oliver Janssen (EPFL)

KSW2.pdf

14:50 Charged quantum-corrected black holes in dS3

In this talk, I will present methods to construct exact solution to the semiclassical back-reaction problem in (2+1)-dimensional asymptotically de Sitter spacetime within the formalism of braneworld holography. In particular, starting from an AdS$_4$ C-Metric, I will describe how to construct a black hole solution that localises on an end-of-the-world brane which. From the lower-dimensional perspective, the black hole can be interpreted as the solution to an higher curvature theory of gravity sourced by a CFT. I will, then, allow for electric and magnetic charge in the bulk, and study their counterintuitive effects on the brane, together with the enriched horizon structure of the geometry. We conclude by describing how the thermodynamics of the bulk system doubles as thermodynamics of the brane solution.

Speaker: Emanuele Panella

Panella_quantum_dS3_eurostrings.pdf

15:10 de Sitter Connectivity from Holographic Entanglement

Considering two antipodal observers in de Sitter space, we illustrate how spacetime connectivity between the holographic screens located on the (stretched) horizons emerges from holographic entanglement. To do so, we construct a covariant holographic entanglement entropy prescription in de Sitter space, including quantum corrections. Entanglement wedge reconstruction implies an extension of static patch holography where the exterior region connecting the static patches is included, and reconstructible from the two screens. A phase transition occurs where there is an exchange of dominance between two competing quantum extremal surfaces, leading to a transfer of the encoding of the exterior region from one screen to the other. If time allows it, we will discuss a generalization to closed FRW cosmologies.

Speaker: Victor Franken

Eurostrings_Franken.pdf

14:00 → 15:30 Parallel sessions: Generalized symmetries

Convener: [Convener: Lakshya Bhardwaj]

14:00 Categorical Landau Paradigm

Landau's paradigm for understanding phase diagrams of quantum systems occupies a central place in theoretical physics. Quantum states are organised into phases characterized by patterns of spontaneous breaking of global symmetries. Despite its successes, severe limitations of this paradigm have been uncovered over the last decades with the discovery of an increasing number of phases of matter that cannot be explained within this paradigm. I will advocate that a solution out of this puzzle may be to generalise the Landau paradigm by incorporating spontaneous breaking of generalised symmetries. I will present the results of recent studies on generalised Landau paradigm for non-invertible symmetries that are characterized mathematically using category theory, due to which this generalisation is referred to as the 'Categorical Landau Paradigm'. These studies provide a description of all possible gapped and gapless phases for systems exhibiting such symmetries, fitting them together into a Hasse phase diagram, along with concrete lattice models realising the aforementioned phases in the infrared; thus demonstrating that the categorical Landau paradigm vastly expands the landscape of quantum phases that can be explained theoretically in terms of spontaneous breaking of global symmetries.

Speaker: Lakshya Bhardwaj

Eurostrings 2024.pdf

14:30 Polarization Pairs and Non-invertible Duality Defects across Dimensions

A (2k)-dimensional quantum field theory involving self-dual (k-1)-form gauge fields a priori defines a relative QFT; the partition function is not scalar-valued when evaluated on closed spacetime manifolds. It is necessary to pick a polarization of the intermediate defect group to have a well-defined, or absolute, QFT. Once the polarization is chosen the resulting theory has a (k-1)-form symmetry. If the (k-1)-form symmetry is gaugeable, it is useful to introduce the polarization pair, which resolves an ambiguity under the gauging of the (k-1)-form symmetry. I will introduce the polarization pair and discuss its connection to concepts like the symmetryTFT and non-invertible duality defects. Furthermore, I will discuss how we can use the polarization pair to learn about the structure of non-invertible symmetries "across dimensions". This talk is based on previous and upcoming work with Xingyang Yu and Hao Zhang.

Speaker: Craig Lawrie

2024-09-Eurostrings.pdf

14:50 Gapped phases and phase transitions with categorical symmetries

Recently, the notion of symmetry has been vastly generalised, coming to include what are now known as categorical, or non-invertible symmetries. In this talk, I will present a framework to study gapped infra-red phases of theories that have such categorical symmetries, which relies on the so-called Symmetry Topological Field Theory (SymTFT). This is a (d+1)-dimensional topological theory associated to a d-dimensional theory that neatly encodes its symmetry properties and has emerged as a key tool to study generalised symmetries. After introducing the concept of SymTFT, I will show how we can use it to extract information on the gapped phase, such as the number of vacua, the action of the symmetry on such vacua, and the order parameters. Focusing on (1+1)-dimensions, I will also introduce a generalisation of the SymTFT that allows us to characterise phase transitions between such gapped phases. This framework thus provides a generalised version of the Landau paradigm for symmetries that go beyond the standard group case.

Speaker: Lea Bottini (University of Oxford)

Eurostrings_Bottini.pdf

15:10 Non-Invertible Symmetries, Anomalies and Scattering Amplitudes

We show that crossing symmetry of S-matrices is modified in certain theories with non-invertible symmetries or anomalies. Focusing on integrable flows to gapped phases in two dimensions, we find that S-matrices derived previously from the bootstrap approach are incompatible with non-invertible symmetries along the flow.
We present various examples and show how the preserved non-invertible symmetries give constraints on the S-matrix bootstrap.

Speaker: Christian Copetti (Oxford)

Talk_Strings.pdf

14:00 → 15:30 Parallel sessions: Holography

Convener: [Convener: Shira Chapman]

14:00 Holographic AdS5 correlators for LLM geometries

We use the supergravity technique to compute heavy-heavy-light-light (HHLL) four-point correlation functions of operators in 4D N=4 Super Yang-Mills (SYM) theory. We compute the two-point function of light probe operators in the background of Lin-Lunin-Maldacena (LLM) geometries dual to heavy operators, thus avoiding the use of Witten diagrams. By taking a limit of the HHLL correlators, we also obtain all-light LLLL four-point correlators.

In particular, we consider LLM geometries generated by profiles which are ripple deformations of a circle. These are dual to coherent superpositions of chiral primary operators of N=4 SYM. For the light probe, we use the dilaton field, which is dual to a descendant of a chiral primary.

We perform the analysis of the correlators both in position space and in Mellin space, and use a Ward identity to compare them with known results for all-light four-point correlators of chiral primaries.

Speaker: Alexander Tyukov (University of Southampton)

EuroStrings24_Tyukov.pdf

14:30 Semiclassical black hole microstates

We study infinite families of black hole microstates consisting of wormholes and shells of matter. They are orthogonal at leading order in the saddle point approximation of the Euclidean gravitational path integral, suggesting a dramatic overcounting of the dimension of the microcanonical subspace. However, wormhole contributions in higher moments of the overlaps reveal small off-diagonal components. This non-orthogonality reduces the (naively infinite) dimension of the space spanned by these states to the expected result: the exponential of the Bekenstein-Hawking entropy. In addition, the appearance of null states can be leveraged to provide evidence of factorization of the bulk Hilbert space of gravity with two asymptotically AdS boundaries at the semiclassical level, generalizing previous results in JT gravity to higher dimensions.

Speaker: Mr Juan Hernandez (Vrije Universiteit Brussel)

Hernandez - Eurostrings 2024.pdf

14:50 Nambu-Goto equation from three-dimensional gravity

In this talk, I will demonstrate that the solutions of three-dimensional gravity obtained by gluing two copies of a spacetime across a junction constituted of a tensile string are in one-to-one correspondence with the solutions of the Nambu-Goto equation in the same spacetime up to a finite number of rigid deformations. The non-linear Nambu-Goto equation satisfied by the average of the embedding coordinates of the junction emerges directly from the junction conditions along with the rigid deformations and corrections due to the tension. Therefore, the equivalence principle generalizes non-trivially to the string. Our results are valid both in three-dimensional flat and AdS spacetimes. In the context of AdS_3/CFT_2 correspondence, our setup could be used to describe a class of interfaces in the conformal field theory featuring relative time reparametrization at the interface which encodes the solution of the Nambu-Goto equation corresponding to the bulk junction.

Speaker: Avik Banerjee (University of Crete)

Avik_slides.pdf

15:10 Exploring Cosmic Censorship in a Collider

I present a new mechanism to generate large curvatures in asymptotically AdS spaces, in rather generic boost invariant setups. On the gravity side, curvature invariants grow in an extended region of spacetime in the bulk. When their values hit Plank scale, the classical approximation breaks down and higher curvature corrections should be taken into account. On the gauge theory side, this signals the breakdown of the holographic description of the dual plasma due to finite N, finite coupling corrections. This is one of the rare instances where quantum gravity effects become significant and observable in a sizable region.

Speaker: Javier Subils (ICCUB - Universitat de Barcelona)

Eurostrings2024v2.pdf

14:00 → 15:30 Parallel sessions: Non-relativistic field theories

Convener: [Convener: Jelle Hartong]

14:00 Non-Lorentzian Geometry and String Theory

I will give an introduction to various non-Lorentzian geometries and their appearance in gravity and field theory. I will then make the case for the study of non-Lorentzian string theories both as limits of ordinary string theory and in their own right. This includes generalisations of the Gomis-Ooguri string (both open and closed) and non-relativistic strings that arise for example via near-BPS limits of the AdS/CFT correspondence (known as spin matrix theory).

Speaker: Jelle Hartong (University of Edinburgh)

Southampton_NRstrings.pdf

14:30 Spin Matrix Theories as Conformal Field Theories

Spin Matrix Theories (SMTs) describe the near-BPS limit of $\mathcal{N}=4$ super Yang-Mills theory, which enables us to probe finite-N effects like D-branes and black hole physics. In the last years, we developed a systematic method to construct SMTs for various limits, including the largest possible case with PSU(1,2|3) invariance. This sector is particularly important because it admits dual black hole solutions, and degenerates to all the other possible SMTs when certain letters of the theory are turned off. In this talk, we make progress to formulate the SMT with PSU(1,2|3) invariance in terms of a three-dimensional non-relativistic quantum field theory. We interpret the result as a non-relativistic conformal field theory, and discuss a corresponding version of the state-operator correspondence.

Speaker: Stefano Baiguera (Ben-Gurion University of the Negev)

Baiguera_SMT.pdf

14:50 Butterflies revisited for asymptotically Lifshitz black hole

We explore connections between two salient chaotic features, namely Lyapunov exponent and butterfly velocity, for the class of asymptotically Lifshitz black hole background with arbitrary critical exponent by implementing three different holographic approaches, namely, entanglement wedge method, out of time-ordered correlators (OTOC) and pole-skipping. We present a comparative study where all of the above methods yield exactly similar results for the butterfly velocity and Lyapunov exponent. This establishes equivalence between all three methods for probing chaos in the chosen gravity background. Explicit non-trivial dependencies of OTOC on the arbitrary critical exponent has also been studied. We further derive the eikonal phase approximation and Lyapunov exponent at the turning point of the null geodesic of the background geometry using the classical approach. These are found as functions of critical exponent. Eventually we uncover different scattering scenarios in the near-horizon and near-boundary regimes.

Speaker: Dr Adrita Chakraborty (AGH University of Science and Technology)

Eurostrings 2024 (1).pdf

15:10 A new non-relativistic holography

Formulating holography in spacetimes obtained via a non-relativistic limit, the so-called Newton-Cartan geometries, is a challenging task that nevertheless gives us access to understanding holography in non-Anti de-Sitter spacetimes. In this talk, I will discuss a recently proposed correspondence between non-relativistic string theory in the String Newton-Cartan version of AdS$_5\times$S$^5$ and Galilean Electrodynamics in 3+1 dimensions with scalar fields. This duality was obtained as a particular stringy non-relativistic limit of the well-known AdS$_5$/CFT$_4$ correspondence, and the dictionary involves a precise match of the infinite tower of non-relativistic symmetries. I will discuss possible quantitative tests, in particular the one regarding matching the string spectrum with the scaling dimension of gauge invariant operators. Time permitting, I will summarise the state of the art of integrability in non-relativistic string theory appearing in this new holographic duality.

Speaker: Andrea Fontanella (Trinity College Dublin)

Fontanella.pdf

14:00 → 15:30 Parallel sessions: Supergravity II

14:00 Supersymmetric localization of N = (2,2) theories on a spindle

There has been recent interest in supergravity solutions which display the singularities of a particular 2-orbifold known as a "spindle". In this talk I will discuss the computation of the partition function of N = (2,2) SQFTs on the spindle via the technique of supersymmetric localization. I will explain how this background avoids the classes of 2-manifolds for which direct N = (2,2) localization has previously been considered and discuss and interpret the computation of 1-loop determinants, making comparison between the unpaired eigenvalue method and the "spindle index" of https://arxiv.org/abs/2312.17086. Time permitting, I will discuss connections with supergravity and accelerating black hole solutions. This talk is based on ongoing work with Augniva Ray, Hyojoong Kim, Imtak Jeon and Nakwoo Kim.

Speaker: Aaron Poole (Kyung Hee University)

AP_Eurostrings.pdf

14:30 NUTs, Bolts, and Spindles

We construct $1/4$-BPS, asymptotically locally hyperbolic Euclidean solutions of $d=4$, $\mathcal{N}=2$ gauged supergravity, describing the total space of orbifold line bundles over a spindle. These $U(1) \times U(1)$-invariant solutions are divided into two classes, corresponding to either the twist or the anti-twist on the spindle-bolt, and generalize the spherical bolts found in arXiv:1212.4618. Consequently, the boundary metrics are squashed, branched lens spaces, and our results provide predictions for the large $N$ limit of the corresponding localized partition functions of the dual superconformal theories.

Speaker: Dr Alessio Fontanarossa (University of Turin)

Eurostrings24_Fontanarossa.pdf

14:50 Holography with conical singularities: black hole entropy from SCFT on the spindle.

We present the first example of holographic matching between the index of a SCFT defined on an orbifold with conical singularities and the entropy of supersymmetric AdS black holes. The orbifold in question is the spindle, which is homeomorphic to the sphere but it has orbifold conical singularities at the poles. We show that the large-N limit of the 3d spindle index of holographic Chern-Simons-matter theories matches the entropy function of accelerating AdS$_4$ black holes. We also discuss higher-dimensional generalizations of this setup.

Speaker: Edoardo Colombo

Edoardo Colombo - Eurostrings 2024 (1).pdf

15:10 SO(9) supergravity in the context of matrix model holography

The BFSS proposal can be understood within the framework of gauge/gravity duality: the holographic dual of matrix theory is a compactification of M-theory in an SO(9)-symmetric pp-wave background. I will present the formalism of holographic renormalization for the matter-coupled two-dimensional maximal supergravity, with fluctuations around a D0-brane geometry. I will discuss the generalisation to its supersymmetric SO(p)xSO(9-p) deformations, for all p. As an application, I will discuss computations of two-point functions for fluctuations in both dilaton and axion sector.

Speaker: Mr Alfred Bovon (Lyon University)

Présentation_Eurostrings_2024_Alfred_Bovon.pdf

15:30 → 16:00 Coffee break

16:00 → 17:30 Plenary session

Convener: [Chair: Michela Petrini]

16:00 On the quantum mechanics of old black holes

The Euclidean gravitational path integral involves a sum over topologies. In this talk, we discuss how topology change can be incorporated into the (Lorentzian) Hilbert space description of quantum gravity. Our proposal leaves the semiclassical space of states intact, but modifies the inner product between them giving rise to a plethora of null states. To illustrate the use of this formalism, we construct the black hole interior volume operator in two-dimensional Jackiw-Teitelboim gravity, compute its expectation value at late times, and discuss its relation to holographic complexity.

Speaker: Mark Mezei (University of Oxford)

Eurostrings_mezei.pdf

Eurostrings_mezei.pptx

16:30 Higher-form symmetries and the A-twist

I will discuss recent progress in understanding global aspects of the path integral of 3d (or 4d) supersymmetric gauge theories with four supercharges on compact spaces. For simply-connected (or unitary) gauge groups, the so-called Bethe-vacua method allows one to compute many supersymmetric observables in terms of a lower-dimensional 2d TQFT, the topological A-twist of an effective 2d gauge theory. I will explain how to generalise the A-twist formalism in the case when the gauge group G is not simply connected, which amounts to gauging a 1-form symmetry. This leads us to new results and to simplifications of old results, including for pure Chern-Simons theory. For instance, we will discuss the Witten index of the (SU(N)/Z_r)_K theory for any allowed set of integers N, r and K. We will also discuss compactification on the most general supersymmetric manifolds in 3d and 4d.

Speaker: Cyril Closset

eurostrings-2024-Closset.pdf

17:00 QFT Dynamics from CFT Data

While quantum field theory has given us a successful description of physical phenomena at many different length scales, almost all computations are currently limited to systems which are weakly-coupled. I will present a new theoretical framework for solving general strongly-interacting physical systems, which uses universal short-distance CFT data to numerically compute long-distance QFT observables. After presenting a general framework which can be applied to quantum field theories in any number of dimensions, I will then discuss its application to multiple strongly-coupled systems, focusing in particular on recent results studying non-equilibrium dynamics at finite temperature and nonperturbative scattering.

Speaker: Matthew Walters (Heriot-Watt University)

QFTfromCFT_Eurostrings.pdf

Friday 6 September

09:00 → 10:00 Review talk

Convener: [Chair: Neil Lambert]

09:00 AdS String Amplitudes and their high energy limit

Speaker: Luis Fernando Alday

Eurostrings (3).pdf

10:00 → 10:30 Plenary session

Convener: [Chair: Neil Lambert]

10:00 Scattering amplitudes for Kerr black holes and higher-spin symmetry

In a series of recent works it has become clear that quantum scattering amplitudes can be used to gain useful insights into the dynamics of Kerr black holes. A simple infinite family of three-point amplitudes has been found, which describes the primary gravitational interaction of a black hole with quantum spin s. However, the corresponding family of Compton four-point amplitudes has not yet been established, except for a few low-spin examples. These amplitudes are needed for post-Newtonian and post-Minkowskian calculations of binary black-hole systems. Interestingly, the Kerr three-point amplitudes can be uniquely predicted from the principle of higher-spin gauge symmetry. I will discuss the construction of a family of EFTs with Stuckelberg higher-spin fields, which enjoy massive higher-spin gauge symmetry, and that describe the Compton dynamics of Kerr black holes, including non-minimal interactions. I will also use insights from a chiral-field approach that is particularly helpful in ensuring correct degrees of freedom. A Compton amplitude to all orders in spin is obtained, and I will discuss the matching to explicit GR calculations.

Speaker: Henrik Johansson

EuroStrings2024 (2).pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Plenary session

Convener: [Chair: Koenraad Schalm]

11:00 Phase shift and two-sided geodesics

We discuss the phase shift of a light particle moving in an AdS black hole geometry. We investigate the physics for impact parameter values beyond the critical one where the particle does not return to the boundary.

Speaker: Manuela Kulaxizi

Eurostrings 2024.pdf

Eurostrings 2024 v1.pdf

11:30 Linear dynamical instabilities and the laws of thermodynamics

Phases of matter can be subject to various instabilities. I will show that interacting systems with a hydrodynamic regime at late times and long distances are dynamically stable under linear perturbations provided the matrix of static susceptibilities is positive definite and the second law of thermodynamics is obeyed. The argument holds irrespective of boost symmetries, extends to theories with only approximate or spontaneously broken global symmetries. A concrete example is the Landau instability of superfluids at large superflow, which can be recast as a thermodynamic instability irrespective of any underlying quasiparticle description.

Speaker: Blaise Goutéraux

Eurostrings-2024-GOUTERAUX.pdf

12:00 Bootstrapping relativistic transport from causality

As an effective field theory, relativistic hydrodynamics is fixed by symmetries up to a set of transport coefficients. In this talk, I will explain how microscopic causality leads to the existence of the hydrohedron: a universal convex geometry in the space of transport coefficients that contains every consistent theory of relativistic transport. I will analytically construct cross-sections of the hydrohedron corresponding to bounds on transport coefficients that appear in sound and diffusion modes for theories without stochastic fluctuations, including all large N holographic QFTs.

Speaker: Alexandre Serantes Rubianes (Ghent University)

Eurostrings-talk_Alex-Serantes.pdf

12:30 → 14:00 Lunch break

14:00 → 15:30 Parallel sessions: AI & machine learning

14:00 Non-perturbative Quantum Physics and Deep Learning

After a brief overview of some of the recent developments in the field of Machine Learning and AI, I will discuss the potential use of such techniques in theoretical High Energy Physics with special emphasis on Quantum Field Theory. I will demonstrate relevant concepts with a specific novel application of Neural Operators in the context of S-matrix theory.

Speaker: Costis Papageorgakis (Queen Mary University of London)

Papageorgakis_eurostrings.pdf

14:30 Learning Integrable Models. From numerics to exact result

In my talk, I will introduce a novel AI-based approach to Integrable Models. I will demonstrate how neural networks can be employed to numerically solve the Yang-Baxter equation and discover new integrable spin-chains. The Hamiltonians of these spin-chains form projective varieties, and I will show how, by using the Boost operator construction for conserved charges, we derive their analytical forms from the approximate numerical data obtained by the neural network. Finally, I will briefly discuss the extension of our method to 2D Integrable Quantum Field Theories.

Speaker: Dr Evgeny Sobko (London Institute for Mathematical Sciences)

EuroStrings2024 (1).pdf

14:50 Computation of Fermion Masses and Mixing in Geometric String Compactifications

The talk will outline recent progress in identifying realistic models of particle physics in heterotic string theory, supported by several mathematical and computational advancements which include: analytic expressions for bundle valued cohomology dimensions on complex projective varieties, heuristic methods of discrete optimisation such as reinforcement learning and genetic algorithms, as well as efficient neural-network approaches for the computation of Ricci-flat metrics on Calabi-Yau manifolds, hermitian Yang-Mills connections on holomorphic vector bundles and bundle valued harmonic forms. I will present a proof of concept computation of quark masses in a string model that recovers the exact standard model spectrum.

Speaker: Andrei Constantin

Constantin (1).pdf

15:10 [cancelled] Reinforcement Learning-based numerical approaches for the Conformal Bootstrap

I will discuss stochastic optimisation techniques for numerically solving the crossing equations within the conformal bootstrap programme. This approach is informed by the use of Reinforcement Learning algorithms. I will present results for a 1D line-defect CFT but also highlight its wider applicability.

Speaker: Costis Papageorgakis (Queen Mary University of London)

14:00 → 15:30 Parallel sessions: CFT

14:00 Orbifold Averages

My talk will be based on work done together with Hans Jockers, Joshua
Kames-King, Alexandros Kanargias and Ida Zadeh. We consider toroidal
Z2 orbifold CFT's. If the Z2 acts not on all directions simultaneously
one distinguishes factorisable versus non-factorisable
orbifolds. Their moduli spaces will be discussed. Expressions for
averaged one loop partition functions will be given. The
talk will conclude with speculations about three dimensional theories
as prospective duals to these averaged ensembles.

Speaker: Stefan Forste (Bonn University)

talk.pdf

14:30 Modulated instabilities and the AdS2 point in dense holographic matter

We investigate the effect that a Chern-Simons term has on the phase diagram of quark matter at finite density and temperature. We carried out the complete fluctuation analysis of the chirally symmetric black hole phase of the bottom-up holographic model V-QCD which models the deconfined phase of QCD. We classify all fluctuations and therefore all quasi-normal modes.

We also analyse the fluctuations at the $AdS_2$ IR point, which realizes the quantum critical line of the dual theory at zero temperature and finite density. We computed the dimensions of the fluctuations in the corresponding one-dimensional IR CFT, and showed how the (purely imaginary) QNMs of the black hole phase map to these $AdS_2$ modes as the temperature approaches zero.

As it turns out, the Chern-Simons term in V-QCD introduces a strong Ooguri-Park instability at finite temperature and chemical potential, but only at finite momentum. We finally investigate the region in which the instabilities appear in the phase diagram.

Speaker: JESUS CRUZ ROJAS (APCTP)

QNM_presentation EuroSTRINGS.pdf

14:50 Renormalization of Conformal Correlators and its Implications

Conformal invariance implies strong constraints on the form of correlation functions of gauge invariant operators, and these correlators diverge when their conformal dimensions satisfy certain relations. These divergences and their renormalization has been understood up to three-point functions in general dimension, and for specific dimensions for holographic 4-point function in d=3. Going from odd to even dimensions increases the complexity of the analysis and in this work we discuss how to renormalize holographic 4-point functions in d=4. The analysis shows that new features arise and renormalization may impose constraints on the spectrum of the CFT.

Speaker: Ms Pratyusha Chowdhury (University of Southampton)

Eurostrings_2024_PratyushaChowdhury.pdf

15:10 Constraining boundary conditions in non-rational CFTs

There are many aspects of 2D conformal field theories where we have a good understanding and powerful tools in the rational (RCFT) case, but these don't always apply to non-rational CFTs. As a laboratory to study these distinctions, we revisit conformal boundary states in the compact free boson CFT. At radii which are irrational multiples of the self-dual radius, an exceptional set of boundary states appear (we call them Friedan-Janik states) in the literature, but they have some undesirable properties, including a continuous spectrum of boundary operators and a divergent g-function. We discuss some arguments about how to interpret these boundary states, how they fit with sewing conditions such as the cluster condition, and derive an explicit closed-form expression for the density of states $\rho(h)$ for the boundary operators. This also lets us explore how the spectrum goes from continuous to discrete in certain limits where we expect to recover such behavior.

Speaker: Hassaan Saleem (SUNY Albany)

Eurostrings talk.pdf

14:00 → 15:30 Parallel sessions: Holography (flat) III

14:00 Spinning Massive Amplitudes from the Flat Limit of CFT Correlators

We analyse the flat limit of AdS using the momentum space CFT representation of correlators. We consider an effective field theory of complex massive spin-1 fields interacting with an abelian gauge field on an asymptotically Anti-de Sitter background and implement the holographic renormalization procedure to compute the boundary CFT 3-point function involving a conserved current and two non-conserved operators with the same, but arbitrary, conformal dimension.

This result agrees with the momentum space CFT 3-point function obtained by solving the conformal Ward identities, providing a non-trivial test of the AdS/CFT correspondence. We discuss the flat limit of this theory by taking the AdS radius and operator dimensions to infinity. In this limit, the CFT 3-point function reduces to the flat space 3-point amplitude with an energy-conserving delta function emerging from the flat limit of triple-K integrals.

Speaker: Dr Raffaele Marotta

Eurostring2024v5pptx.pdf

Eurostring2024v5pptx.pptx

14:30 Soft factorization of scattering processes on AdS spacetimes

Scattering amplitudes can be recovered in the AdS/CFT correspondence from CFT correlation functions by taking an infinite radius limit of the AdS spacetime. In this talk, I will discuss the soft factorization of scattering amplitudes in this limit. We first use `classical soft theorems' to establish that soft photon and soft graviton factors involve inverse AdS radius corrections of the known leading flat spacetime soft factors. We then apply the AdS/CFT correspondence to derive the leading inverse AdS radius corrected soft photon factor from the U(1) Ward identity of a CFT. I'll conclude with a discussion on inverse AdS radius corrections of scattering amplitudes about the flat spacetime limit following ongoing work.

Speaker: Karan Fernandes

ES2024_final.pdf

Fernandes_ES2024.pdf

14:50 On-shell Bootstrap for n-gluons and gravitons scattering in (A)dS, Unitarity and Soft limits

We propose an algorithm to recursively bootstrap n-point gluon and graviton Mellin-Momentum amplitudes in (A)dS spacetime using only three-point amplitude. We discover that gluon amplitudes are simply determined by factorization for n ≥ 5. The same principle applies to n-point graviton amplitudes, but additional constraints such as flat space and soft limits are needed to fix contact terms. Furthermore, we establish a mapping from n-point Mellin-Momentum amplitudes to n-point cosmological correlators. We efficiently compute explicit examples up to five points. This leads to the first five-graviton amplitude in AdSd+1.

Speaker: Yuyu Mo (University of Edinburgh)

Eurostring 1.pdf

Eurostring 1.pdf

Eurostring 1.pptx

15:10 Entanglement Rényi entropies in celestial holography

Celestial holography is the conjecture that scattering amplitudes in ($d$+2)-dimensional asymptotically flat spacetimes are dual to correlators of a $d$-dimensional conformal field theory, called the celestial CFT (CCFT). In CFT we can calculate sub-region entanglement Rényi entropies (EREs) from correlators of twist operators, via the replica trick. We argue that CCFT twist operators are holographically dual to cosmic strings or cosmic branes in the ($d$+2)-dimensional spacetime, and that their correlators are holographically dual to the ($d$+2)-dimensional partition function in the presence of these cosmic branes. We compute the EREs of a spherical region of the CCFT's conformal vacuum, finding the form dictated by conformal symmetry.

Speaker: Ronnie Rodgers

rodgers_eurostrings_2024.pdf

14:00 → 15:30 Parallel sessions: QFT II

Convener: [Convener: Christopher Beem]

14:00 Hidden Unitarity in the SCFT/VOA Correspondence

Four-dimensional N=2 superconformal field theories (SCFTs) give rise, via a cohomological construction, to associated vertex operator algebras (VOAs) that have been much investigated in the last decade. A notable feature of this construction is that for unitary parent SCFT, the VOA so realised is non-unitary. In this talk I will describe a novel structure present for these VOAs that encodes unitarity of the parent theory. Like conventional unitarity, this hidden unitarity imposes strong constraints. I will describe efforts to impose this constraint for simple classes of VOAs leading to (conjectural) classification results. [Based on work in progress with Arash Ardehali, Madalena Lemos, and Leonardo Rastelli.]

Speaker: Prof. Christopher Beem (University of Oxford)

CJB Eurostrings 2024.pdf

14:30 Classifying large N limits of multiscalar theories by algebra

We apply our previously developed approach to marginal corrections in QFTs with multiple scalars, which shows that one-loop RG flows can be described in terms of a commutative but non-associative algebra, to various vector, matrix and tensor models in 4D. We show that the algebra can be used to identify the useful scalings of the couplings for taking the large $N$ limit.

Using this method, we classify all large $N$ (and $M$) limits of models such as $O(N)^3$ and the bifundamental model $O(N)\times O(M)$. The algebra identifies these limits without diagrammatic or combinatorial analysis. For a model with $M$ $SU(N)$ adjoint scalars the limits are the standard 't Hooft limit, a ´multi-matrix limit´, a large $M$ finite $N$ limit and two intermediate cases with extra symmetry and no free parameters. The algebraic concepts of subalgebras and ideals are used to characterise the limits. These new limits are yet to be explored at higher loop orders.

Speaker: Nadia Flodgren

Eurostrings2024_Flodgren.pdf

14:50 MTC[M3,G] : 3d Topological Order Labeled by Seifert Manifolds

We propose a correspondence between topological order in 2+1d and Seifert three-manifolds together with a choice of ADE gauge group $G$. Topological order in 2+1d is known to be characterized in terms of modular tensor categories (MTCs), and we thus propose a relation between MTCs and Seifert three-manifolds. The correspondence defines for every Seifert manifold and choice of $G$ a fusion category, which we conjecture to be modular whenever the Seifert manifold has trivial first homology group with coefficients in the center of $G$.
The construction determines the spins of anyons and their S-matrix, and provides a constructive way to determine the R- and F-symbols from simple building blocks.
We explore the possibility that this correspondence provides an alternative classification of MTCs, which is put to the test by realizing all MTCs (unitary or non-unitary) with rank $r\leq 5$ in terms of Seifert manifolds and a choice of Lie group $G$.

Speaker: Jingxiang Wu (University of Oxford)

MTCs.pdf

15:10 Homotopy algebras in hep-th

Symmetries underlie physics. Often, symmetries do not hold exactly but
only "up to homotopy" (often synonymous with "on shell"), and this
corresponds to the mathematical structure of homotopy algebras (e.g.
L∞-algebras). We explore some of the many instances where such structures appear, including colour-kinematics duality, holomorphic twists, the
Keldysh-Schwinger formalism, and the AdS/CFT correspondence, as time
permits, and how to construct recursion formulas using them.

Speaker: Hyungrok Kim (University of Hertfordshire)

slides.pdf

14:00 → 15:30 Parallel sessions: Resurgence & non-perturbative methods II

Convener: [Convener: Ines Aniceto]

14:00 strong-weak resurgent symmetry and the beauty of L-functions

Quantizing the mirror curve to a toric Calabi-Yau threefold gives rise to quantum operators whose fermionic spectral traces produce factorially divergent formal power series in the Planck constant and its inverse. These are conjecturally captured by the Nekrasov-Shatashvili and standard topological string free energies, respectively, via the TS/ST correspondence. Building on the study by C. Rella on the resurgent structure of the first fermionic spectral trace of local P2, we take the perspective of the Stokes constants and their generating functions. We prove that a full-fledged strong-weak resurgent symmetry is at play, exchanging the perturbative/nonperturbative contributions to the holomorphic and anti-holomorphic blocks in the factorization of the spectral trace. This relies on a global net of relations connecting the perturbative series and the discontinuities in the dual regimes, which is built upon the analytic properties of the L-functions with coefficients given by the Stokes constants and the q-series acting as their generating functions. Based on a joint work with C. Rella arXiv:2404.10695.

Speaker: Veronica Fantini (IHÉS)

Eurostring2024--Fantini.pdf

14:30 An algebraic approach to parametric resurgence

Parametric resurgence plays an important role in the study of physical observables, as in most cases correlators will depend on multiple parameters (such as the coupling and gauge group). In this talk I will discuss recent work in algebraic examples of parametric resurgence. We discuss a simple example to elucidate the so-called higher order Stokes phenomena and discuss how a Borel inner-outer matching procedure allows us to view parametric resurgence as a series of non-parametric resurgent problems.

Speaker: Mr Samuel Crew (Imperial college)

Eurostrings Talk.pdf

14:50 Localization and resummation in 2d Yang-Mills

In this talk, I will present the all-orders perturbative expansion of the partition function of 2d Yang-Mills on arbitrary closed surfaces around unstable instantons, i.e. higher critical points of the classical action. I will describe two approaches to this result: through resummation of the lattice partition function, and through non-standard supersymmetric localization. The result of localization is a novel effective action that is itself a distribution rather than a function of the supersymmetric moduli.

Speaker: Dr Rodolfo Panerai (University of Cologne)

Panerai - Eurostrings 2024.pdf

15:10 Strong coupling expansion of determinant observables in supersymmetric gauge theories

A special class of observables in N=4 and N=2 SYM can be expressed as determinants of semi-infinite matrices. At strong coupling, the expansion of these observables are asymptotic. The perturbative coefficients was already determined in the literature. We have established a method to systematically calculate the non-perturbative part as well. It is based on the fact that the elements of the defining matrices are given by truncated Bessel kernels. Their structure provide several constraints to the observables in forms of differential and integral equations. Using them and the analyticity properties of the kernel the entire asymptotic series can be determined.

Speaker: Bercel Boldis (HUN-REN Wigner Research Centre for Physics, Budapest University of Technology and Economics)

presentation_BBoldis.pdf

presentation_BBoldis.pptx

15:30 → 16:00 Coffee break

16:00 → 17:30 Plenary session

Convener: [Chair: Nick Evans]

16:00 A Resurgence of Negativity in Large N Duality

The large N expansion yields an asymptotic series. Standard (exponentially suppressed) nonperturbative corrections associated with this series are driven by eigenvalue tunneling. However there are equally relevant exponentially-enhanced nonperturbative-corrections driven by anti-eigenvalue tunneling, which play a key role in describing the asymptotic properties of the large N expansion, as well as the physics of the large N theory across the complex ’t Hooft-coupling plane. The same holds true for the string theoretic free energy, where there are now both D-branes and negative-tension D-branes contributing to both the asymptotics and the physics of rather generic problems. After discussing these new nonperturbative effects and the role they play, we turn to their consequences. Partition functions of very generic matrix models and non-critical string theories (with arbitrary KdV times) may be written in closed-form (starting off from string equations alone) via the use of resurgence, transseries, and the aforementioned complete nonperturbative contributions. These have the natural form of Nekrasov-Okounkov dual partition functions, and their associated complete Stokes data can be analytically computed (anywhere on the KdV hierarchy). By examining resonant (kernel) directions in the transseries, a (dual) description of topological strings emerges, which allows for the computation of Argyres-Douglas observables again starting-off solely from string equations (both differential/double-scaled and finite-difference/off-critical). These results for the free energy and partition function may open the door to the exact nonperturbative computation of wave-functions and multi-resolvent operators, eventually fully solving large classes of matrix models and non-critical string theories nonperturbatively.

Speaker: Ricardo Pina Schiappa De Carvalho (Universidade de Lisboa (PT))

EUROSTRINGS2024.pdf

16:30 Rényi entropies in the $n\to 0$ limit, entanglement temperatures and holography

In this talk, I will introduce the notion of entanglement temperatures in QFT, a generalization of the Unruh temperatures valid for states reduced onto arbitrary spatial regions. The entanglement temperatures encode the high energy behavior of the state around a point and are determined by the solutions of an Eikonal problem in Euclidean space. I will show that for theories with a UV fixed point, the entanglement temperatures determine the state with a large modular temperature. In particular, I will derive a formula that connects the Rényi entropy in the small Rényi parameter limit and the entanglement temperatures.

In two dimensions, the entanglement temperatures are universal, and so are the associated states. I will show that this fact in conjunction with holography leads to a simple description of the holographic Renyi entropies in the small Rényi parameter. I will comment on the generalization to arbitrary dimension, as well as, open questions and future directions.

Speaker: Cesar Agon

Renyi-0-ET-holo.pdf

17:00 A compendium of logarithmic corrections in AdS/CFT

I will discuss logarithmic corrections to various CFT partition functions in the context of the AdS_4/CFT_3 correspondence for theories arising on the worldvolume of M2-branes. I will use four-dimensional gauged supergravity and heat kernel methods to derive general expressions for the logarithmic corrections to the gravitational on-shell action or black hole entropy for a number of different supergravity backgrounds. I will outline several subtleties and puzzles in these calculations and will show how they provide non-trivial precision tests of the AdS/CFT correspondence. These results have important implications for the existence of scale separated AdS vacua in string theory and for effective field theory in AdS more generally.

Speaker: Nikolay Bobev (KU Leuven Association)

Eurostrings2024.pdf

17:30 → 18:00 Concluding remarks

17:30 Remarks on fpuk

Speaker: Neil Lambert

Presentation.pdf

17:45 Closing remarks

eurostrings-25-slide[2].pdf