EUROSTRINGS 2025 - COST Action Theory-Challenges General Meeting

25 Aug 2025, 08:00 → 28 Aug 2025, 18:20 Europe/Stockholm

Auditorium 5 (Albano Building 2)

Pawel Caputa, Michele Del Zotto (Uppsala University), Magdalena Larfors (Uppsala University), Pietro Longhi (Uppsala university), Anton Nedelin (King's College London), Niels Obers (Niels Bohr Institute), Alessandro Sfondrini (Padua University), Watse Sybesma (University of Cambridge), Maxim Zabzine (Uppsala university), Konstantin Zarembo (Stockholm University)

Scope

Eurostrings is a series of annual conferences gathering researchers from all over Europe and elsewhere, working on string theory, gauge/gravity duality, quantum gravity and quantum field theories, and the relations among them. Previous Eurostrings conferences were held in Southampton, Gijon, Lyon, London, Milano, Leuven, Cambridge.

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Themes and program schedule

The conference will feature both review and research talks reflecting recent developments in research on String Theory. 

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Invited speakers

Review talks:
Sameer Murthy (King's College London)
Sakura Schafer-Nameki (Oxford University)
Roberto Tateo (University of Turin)

Plenary talks:
Agnese Bissi (ICTP Trieste/Uppsala University)
Lorenz Eberhardt (Amsterdam University) 
Yolanda Lozano (University of Oviedo)
Andre Lukas (Oxford University)
Martin Sasieta (Brandeis University)
Oliver Schlotterer (Uppsala University)
Fiona Seibold (DESY)
Andy Svesko (King's College London)
Irene Valenzuela (CERN)
Balt van Rees (Ecole Polytechnique) 
Benoit Vicedo (University of York)
Ziqi Yan (Nordita)

Contributed talks:
Ankit Aggarwal (TU Wien)
Guillermo Arias-Tamargo (Imperial College)
Erica Bertolini (Dublin Institute for Advanced Studies)
Ilija Buric (Trinity College Dublin)
Franz Ciceri (École normale supérieure, Lyon)
Andrea Dei (Chicago University)
Davide Fioravanti (University of Bologna)
Jackson Fliss (Cambdirge University)
Julius Grimminger (Oxford University)
Romuald Janik (Jagiellonian University)
Falk Hassler (University of Wrocław)
Emil Have (Niels Bohr Institute)
Troels Harmark (Niels Bohr Institute)
Johan Henriksson (CERN)
Jani Kastikainen (Wurzburg University)
Maria Knysh (Vrije Universiteit Brussel)
Ziwen Kong (DESY)
Yixuan Li (University of Padua)
Jeremy Mann (King's College London)
Victor Mishnyakov (Nordita)
Pierluigi Niro (SISSA)
Alexia Nix (University of Iceland)
Davide Polvara (Hamburg University)
Bo Sundborg (Stockholm University)
Fridrich Valach (Charles University)

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Outreach public lecture

The Role of Science in Times of Geopolitical Uncertainties

Title: Impact of Geopolitics on COST
Speaker: COST Director Ronald De Bruin

Title: Science at the Crossroads: Promises and Perils
Speaker: ISC President-elect Robbert Dijkgraaf

Date: Tuesday August 26 
Click here for registration and further information.

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Satellite event

The meeting will be combined with a 1-day Fest for Joe Minahan on Friday, where the talks will be centered around Joe's research interests. Participants at Eurostrings are invited to attend the Friday talks, at no extra cost.

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Dates and Venue

Aug 25-28, Auditorium 5, Albano Campus building 2, Stockholm, Sweden.

Note: this event will be livestreamed on the Action's YouTube Channel:

   https://www.youtube.com/@TheoryChallenges

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Registration

Registration for this event is now closed.

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Advisory Committee

Pablo Bueno, Roberto Emparan, Daniel Grumiller, Henrik Johansson, Elias Kiritsis, Charlotte Kristjansen, Yolands Lozano Gomez, Fernando Marchesano, Ricardo Monteiro, Sara Pasquetti, Silvia Penati, Michela Petrini, Boris Pioline, Jan Plefka, Andrea Puhm, Diego Rodriguez Gomez, Henning Samtleben, Koenraad Schalm, Andreas Stergiou, Antoine Van Proeyen.

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The COST Action

The aim of the COST Action "Fundamental Challenges in Theoretical
Physics" is to develop a comprehensive approach for studying
strongly-interacting systems in classical and quantum physics. The
Action brings together theoretical and mathematical physicists with
expertise in quantum field theory, string theory, gravity, geometry and
information theory, establishing the first network of this kind centred
around Europe. You can join the action by clicking here.

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COST Leadership

Alessandro Sfondrini (Action Chair), Piotr Sułkowski (Action Vice-chair), Diego Rodriguez-Gomez, Predrag Dominis Prester, Nicolaos Toumbas, Martin Cederwall, Riccardo Borsato, Nils Carqueville.

 

Sponsored by:

                             

   

Monday 25 August

1 Registration

2 Welcome

3 Recent Progress on Generalized Symmetries

Speaker: Sakura Schafer-Nameki (University of Oxford)

4 Computing Yukawa couplings from string theory

I will discuss how to compute Yukawa couplings in realistic heterotic string models, using machine learning techniques. More specifically, I will explains how training of neural networks can be used to find the main geometrical ingredients of string theory Yukawa couplings, namely approximate Ricci-flat metric on Calabi-Yau manifolds, Hermitian Yang-Mill connections and harmonic bundle-valued forms. The techniques are illustrated for a specific string model with a low-energy standard model spectrum.

Speaker: Andre Lukas (University of Oxford)

11:10 Coffee break

5 Evaluating one-loop string amplitudes

I will explain a general technique that evaluates one-loop string amplitudes exactly in terms of an infinite series originating from certain Lorentzian singularities in moduli space. It is based on a non-holomorphic extension of the Rademacher procedure that applies to any integral of a modular function (with certain boundedness conditions). I will then discuss the concrete example of the one-loop four-graviton scattering amplitude for type II superstrings and the physics we can extract from these methods. This talk is based on joint work with M.M. Baccianti, J. Chandra, T. Hartman and S. Mizera.

Speaker: Lorenz Eberhardt (University of Amsterdam)

6 AdS3/CFT2 and defect CFTs

I will discuss recent interpretations of AdS3 solutions as holographic duals of surface defect CFTs. One solution will be interpreted as an extension of ABJM to the massive case, in which one of the external directions becomes an energy scale and generates a flow towards an AdS3 space. A second solution will be related to surface defects embedded in 6d (1,0) CFTs living in D6-NS5-D8 brane intersections. In this second example we will find an interesting connection with the phenomenon of deconstruction.

Speaker: Yolanda Lozano (University of Oviedo)

13:00 Lunch break

7 N-body problem in AdS at large spin

Quantum field theory in Anti de Sitter space (AdS) is a useful framework to study conformal field theories (CFTs). In this context, I will focus on the spectrum of lowest-energy N-particle states at fixed spin, which exhibit universal properties in the large-spin limit. In the absence of interactions, the states are bound by the AdS curvature, and have a degeneracy similar to the Landau levels of particles in a magnetic field. In perturbation theory, the degeneracy is lifted by a quantum mechanical N-body Hamiltonian on the hyperbolic disk. Using the theory of Berezin-Toeplitz quantization and cross-checks with exact diagonalization, I will show that the large-spin limit is semiclassical, with explicit predictions for the density of states and lowest-lying energies. As an outlook, I will comment on how this semiclassical description can be derived for general CFTs. Based on 2412.12328 with Petr Kravchuk and further work in progress.

Speaker: Jeremy Mann (King's College London)

8 Integral Identities from Symmetry Breaking of Conformal Defects

Symmetry-breaking is an innate nature of defects. There is a distinguished set of defect operators that keeps track of the symmetries in the parent conformal field theory broken by the defect insertion, such as the tilt operators and displacement operators. We find identities of such defect operators between their 2-pt functions and integrated 4-pt functions (and higher ones), based on either the geometric properties of the defect conformal manifold which is the symmetry-breaking coset, or the Lie algebra of corresponding broken symmetry generators. I will demonstrate these integral identities in the case of the 1/2 BPS Maldacena-Wilson loop in N = 4 SYM as an example.

Speaker: Ziwen Kong (DESY)

9 Holographic duality from Howe duality: Chern-Simons gravity as an ensemble of code CFTs

Recent advances indicate that 3d gravity may be dual not to a single CFT but to an average over an ensemble of CFTs. We consider a concrete ensemble of CFTs deriving from error-correcting codes via a lattice construction. The very same ensemble also arises from 3d abelian Chern-Simons theory by the gauging of maximal subgroups of the bulk one-form symmetry. Remarkably, the ensemble average over such CFTs agrees with "Chern-Simons gravity," a bulk theory summed over 3d topologies sharing the same boundary, i.e. a Poincaré series akin to that in semiclassical gravity. Here we relate this correspondence to Howe duality, a mathematical framework concerning the representations of two commuting groups. This framework is known to be behind Siegel-Weil formulas underpinning other instances of holography by averaging. Using recent mathematical results from Howe duality for finite fields, we are able to rigorously prove the duality between the code CFT ensemble and Chern-Simons gravity, exhibiting a proof valid at any genus and central charge.

Speaker: Johan Henriksson (CERN)

15:30 Coffee break

10 Non-invertible symmetries of Non-Linear Sigma Models

Global symmetries can be generalised to transformations generated by topological operators, including cases in which the topological operator does not have an inverse. A family of such topological operators are intimately related to dualities via the procedure of half-space gauging. In this work we discuss the construction of non-invertible defects based on T-duality in two dimensions, generalising the well-known case of the free compact boson to any Non-Linear Sigma Model with Wess-Zumino term which is T-dualisable. Our approach allows us to include target spaces without non-trivial 1-cycles, does not require the NLSM to be conformal, and when it is conformal it does not need to be rational; moreover, it highlights the microscopic origin of the topological terms that are responsible for the non-invertibility of the defect. An interesting class of examples are Wess-Zumino-Witten models, which are self-dual under a discrete gauging of a subgroup of the isometry symmetry and so host a topological defect line with Tambara-Yamagami fusion. Time permitting, I'll discuss the target space interpretation of these defects, and their fate in String Theory.

Speaker: Guillermo Arias-Tamargo (Imperial College London)

11 Aspects of QED in 2+1 dimensions

QED in 2+1 dimensions is among the simplest and yet very rich examples of strongly interacting gauge theories, arising in many physical contexts. When the number of electrons is large, the theory is known to flow to a symmetry-preserving interacting CFT at low energies, but there is evidence that this scenario is excluded below some critical value of the number of electrons. Focusing on the case of two electrons, we argue that the theory must then spontaneously break its U(2) global symmetry to a U(1) subgroup via the condensation of monopole operators. This gives rise to a non-linear sigma model with target space a squashed three-sphere, equipped with a theta term required by anomaly matching. Finally, I will also discuss how this scenario is consistent with deformations of supersymmetric QED with eight supercharges. Based on 2410.05366 with Thomas Dumitrescu and Ryan Thorngren, and on work in progress with Thomas Dumitrescu, Ken Intriligator, and Orr Sela.

Speaker: Pierluigi Niro (SISSA)

17:00 Poster session - Reception

Tuesday 26 August

12 Near-extremal black holes and their microstates

Speaker: Sameer Murthy (King's College London)

13 Finite boundaries in gravity

Boundaries play a foundational role in gravity. In this talk, I will review the novelty of finite timelike boundaries, particularly in the context of gravitational thermodynamics. Specifically, I will demonstrate how finite Dirichlet boundaries resolve prior confusions about the thermal description of the de Sitter static patch. Then I will show that finite conformal boundaries, where the conformal class of the boundary induced metric and the trace of the extrinsic curvature are fixed, yield new kinds of horizon thermodynamics. Notably, systems with cosmological horizons are rendered thermally stable, while the entropy for near-extremal black holes features new scaling laws at low-temperature. Moreover, the effective two-dimensional dilaton-gravity characterizing deviations away from extremality is not JT gravity, and the effective description of a dynamical conformal boundary in 3D gravity looks like Schwarzian theory coupled to one-dimensional quantum gravity.

Speaker: Andrew Svesko (King's College London)

11:10 Coffee break

14 Multiparticle states in CFTs

In this talk discusses the treatment of multi-trace operators in conformal field theories, with a focus on N=4 SYM. We present constraints on four-point functions of protected, double-, and single-trace operators in the large central charge limit. Particular attention is given to the triple-trace sector of the correlator, along with its holographic interpretation.

Speaker: Agnese Bissi (ICTP & Uppsala University)

15 Rigorous results for the lightcone and modular bootstrap

We discuss how to extract mathematically precise predictions for the large spin OPE data in d-dimensional non-rational CFTs, either from crossing symmetry of four-point functions (for d > 2) or from modular invariance (for d = 2).

Speaker: Balt van Rees (Ecole Polytechnique)

13:00 Lunch break

16 Exploring Black Hole Hilbert Spaces through the Gravity Path Integral

The construction of an infinite family of microstates for double-sided black holes in general relativity with a negative cosmological constant has opened a new avenue for investigating black hole properties. These microstates, characterized by shells of matter located behind the horizon, provide a powerful framework for probing the structure of the black hole Hilbert space, including its dimensionality. Using this approach, we demonstrate the factorization of the Hilbert space associated with double-sided black holes, examine out-of-equilibrium fluctuations of black holes, and discuss corrections arising from matter coupled to gravity.

Speaker: Maria Knysh (Vrije Universiteit Brussel (VUB))

17 The Statistics of BPS Chaos

Black hole microstates, considered collectively as an ensemble, are believed to exhibit properties of quantum chaos, and in particular eigenvalue repulsion. The extent of the repulsion characterises how ‘strong’ the chaos is. In this talk, I will focus on the example of the microstates of a supersymmetric black holes with macroscopic horizon, namely the D1-D5-P system. I will explain how the ability to find ‘strong’ or ‘weak’ chaos is related to how the microstates are organised into some particular subgroups, and to the logarithmic corrections of the entropy. Finally, I will show how this organisational problem translates into a statistical-mechanics problem and discuss the physical implications. (Work in progress with N. Ceplak, S. Massai and M. Shigemori.)

Speaker: Yixuan Li (University of Padua)

18 Coulomb Branch of N=4 SYM and Integrability

We study the main properties of N=4 SYM theory at a special point on the Coulomb branch, which corresponds to a U(N) to U(N-1) x U(1) symmetry breaking pattern. We investigate several general questions, using this theory as a toy model: renormalization of operators and one-point functions, convergence of the OPE, and constraints on OPE data. Moreover, in the protected sector, we check the holographic prescription by computing one-point functions at strong coupling and matching them with the perturbative calculation.

Speaker: Victor Mishnyakov (Nordita)

15:30 Coffee break

19 Ising model, gravity and evading the black hole information paradox

We show that the Ising model CFT can be used to obtain some clear insights into 3D (quantum) gravity with matter. We review arguments for the existence of its holographic description, and analyze the time dependence of perturbations of the theory at high temperature, which would correspond to throwing matter into a black hole in the dual gravitational picture. After an initial exponential damping - consistent with absorption by the black hole - the signal remarkably re-emerges again, apparently at odds with the expected black hole behaviour. We use the exact solvability of the Ising model CFT to deduce the behaviour of the bulk matter fields which is responsible for this remergence and thus allows for evading the black hole information paradox.

Speaker: Romuald Janik (Jagiellonian University)

20 Minimal areas from entangled matrices

The geometrization of quantum information lies at the core of holography and of quantum gravity more broadly. In this talk I will illustrate how the entanglement entropy of certain subsystems in matrix quantum mechanics can give rise to a minimization and counting problem exhibiting many similarities to the Ryu-Takayanagi formula. In particular, in states where a non-commutative geometry emerges from semiclassical matrices, the subsystem determines a reduced state which is the sum of density matrices corresponding to distinct spatial subregions, the areas of which count the dimension of maximally entangled edge modes. I will further show how this sum can be dominated by a subregion of minimal boundary area. Central to this result is a notion of coarse-graining that controls the proliferation of highly curved and disconnected non-geometric subregions in the sum.

Speaker: Jackson Fliss (University of Cambridge)

21 Black holes in Higher Spin AdS_4/CFT_3

Higher spin AdS/CFT is intriguing: The phase transition in the boundary theory has been interpreted as a mysterious Planck scale transition in the bulk, rather than as a Hawking-Page transition between blackbody radiation and a black hole. A rich spectrum of heavy operators in the boundary theory have often been overlooked, but we find that the heavy states are closely related to the phase transition.
Independently of these observations, we try a new picture which recovers the duality of the boundary phase transition with a Hawking-Page transition at the AdS scale.

Speaker: Bo Sundborg (Stockholm University)

22 The Role of Science in Times of Geopolitical Uncertainties

Speakers: Robbert Dijkgraaf, Ronald De Bruin

Wednesday 27 August

23 TTbar-like flows and links to string theory

We review a class of integrable irrelevant deformations in two-dimensional field
theories, focusing on TTbar-like flows and their geometric interpretations.
Some of these flows can be exactly solved at the finite-volume spectrum level using
hydrodynamic-type equations, which are closely connected to Nambu–Goto strings and
Jackiw–Teitelboim gravity.
We then discuss how related flow equations emerge in effective field theories of
nonlinear electrodynamics and specific modified gravity models in higher dimensions.

In these cases, exact solvability is generally lost; nevertheless, the TTbar
framework remains a valuable structural guide, suggesting geometric-flow
interpretations and links to Born–Infeld-type actions.

Speaker: Roberto Tateo (Università degli Studi di Torino)

24 Integrable deformations of AdS3 strings

Free strings on backgrounds such as AdS3xS3xT4 and AdS3xS3xS3xS1 can be described by integrable sigma models, which admit a very rich landscape of integrable deformations. In this talk I will focus on TsT, trigonometric and elliptic deformations which preserve some amount of supersymmetry and interpolate between well-known integrable setups, including AdS2 backgrounds. I will present the deformed geometry and check that the S-matrix encoding the scattering of excitations on the string worldsheet is compatible with factorisation.

Speaker: Fiona Seibold (EPFL)

11:10 Coffee break

25 A variational formulation of the Hitchin system

I will present a variational formulation of the Hitchin system on a compact Riemann surface C of arbitrary genus, allowing simple poles in the Higgs field at finitely many points. The hierarchy of time flows is described within the framework of Lagrangian multiforms, which I will briefly review. Adapting Hitchin’s construction — via symplectic reduction of the space of stable holomorphic structures on a principal G-bundle P \to C — to this variational setting naturally produces a multiform version of the action of 3d mixed BF theory with defects, a lower-dimensional analogue of the celebrated 4d semi-holomorphic Chern–Simons theory. Working directly in holomorphic local trivialisations of principal G-bundles yields a simple 1d action that unifies several well-known integrable hierarchies — rational and elliptic Gaudin, including elliptic spin Calogero–Moser — within a single variational framework. This is based on joint work in progress with V. Caudrelier, D. Harland and A. A. Singh.

Speaker: Benoit Vicedo (University of York)

26 A BPS Road to Holography and Matrix Theory

I will discuss recent progress on a framework that unifies BPS decoupling limits in string theory and M-theory, which gives a new perspective on AdS/CFT and matrix theories. This perspective naturally involves non-Lorentzian geometries. I will show how this framework implies generalizations of AdS/CFT, as well as a correspondence between finite-N matrix theory and non-Lorentzian supergravity.

Speaker: Ziqi Yan (Nordita)

13:00 Lunch break

27 Panel on Funding

15:30 Coffee break

28 On the string theory of a single NS5-brane

I will present a worldsheet formulation of string theory in the background of a single decoupled NS5-brane, which is a particularly simple example of ``little string'' holography. The worldsheet theory involves a gauged Wess-Zumino-Witten model for the group coset G/H, where G=PSU(1,1|2)×R^{5,1} and H=U(1)×U(1). A variant of the embedding of H into G describes a background that interpolates between the fivebrane throat in the UV and AdS3 in the IR, which is dual to the (single trace) TTbar-deformed symmetric product orbifold. Well-known difficulties with a worldsheet theory for n_5=1 fivebranes are bypassed by the incorporation of an extra constraint on the dynamics. Along the way, we construct a map between the supergroup formulation of the n_5=1 worldsheet theory and the more conventional RNS worldsheet formalism.

Speaker: Andrea Dei (University of Chicago)

29 Holographic thermal coefficients, KMS condition and black holes

Conformal two-point functions at finite temperature are constrained by the Kubo-Martin-Schwinger (KMS) condition, which expresses periodicity in Euclidean time. Together with the conformal block decomposition, the KMS condition has recently been used to formulate a thermal bootstrap program, leading to various results in the Ising and O(N) models. We show how the KMS condition may be used to obtain double-trace thermal coefficients in holographic theories. The result passes several checks, including a comparison with solutions to the Klein-Gordon equation on the planar AdS black hole. The talk is based on joint works with Ivan Gusev and Andrei Parnachev, 2505.10277 + 2508.08373.

Speaker: Ilija Buric (Trinity College Dublin)

30 Holographic confining theories on space-times with constant positive curvature

Confinement is the phenomenon where quarks at low energies cannot propagate freely, but are confined into bound states of hadrons. At large temperatures hadrons break apart in a transition to a deconfined phase. Such transitions can also be induced by the curvature of the background spacetime, even at zero temperature. In this talk, I investigate curvature induced confinement transitions in QFTs living on positively curved space-times (de Sitter space) using holography. The holographic model consists of Einstein-scalar gravity where the bulk scalar field is assigned a potential that diverges exponentially at large field values. Acceptable interior boundary conditions are defined by requiring the existence of an uplift to a regular solution of higher-dimensional Einstein gravity. We find a competition of two types of saddles and a phase transition between them. We argue that when the leading exponent of the potential is above a certain bound, the transition is first-order, while below the bound, it is higher-order. The talk is based on arXiv:2502.04036 with Elias Kiritsis and Francesco Nitti.

Speaker: Jani Kastikainen (University of Würzburg)

17:05 Break

31 The generalized Cartan Geometry of α'-corrections

α'-corrections appear as higher-derivative correction in the low-energy effective action of string theory and at the same time as loop-corrections in two dimensional σ-models. Despite their importance, we just start to understand their effects on integrability and dualities in string theory. While generalized geometry has been proven central to analyse both at the leading order, a full set of comparable tools is missing for α'-corrections. Currently the most advance approach is the generalized Bergshoeff-de Roo identification (gBdRi) but it is lacking a geometric interpretation which so far has been crucial to understand integrable string models and the web of dualities connecting them. I my talk I will rectify this situation by showing that the gBdRi can be derived from a suitable extension of the Cartan Geometry, which unifies all generalized dualities and their underlying gauged E-models as homogeneous spaces in generalized geometry.

Speaker: Falk Hassler (University of Wrocław)

32 New developments in N=1 D=10 supergravity

We present a full Batalin-Vilkovisky formulation of N=1 D=10 supergravity coupled to Yang-Mills multiplets, in the background independent component field formalism coming from generalised geometry. This is a joint work with Julian Kupka and Charles Strickland-Constable.

Speaker: Fridrich Valach (Charles University, Prague)

19:00 Dinner

Thursday 28 August

33 The CFT Distance Conjecture and Non-Critical Strings

Speaker: Irene Valenzuela (CERN + IFT Madrid)

34 ER for typical EPR

What do the typical entangled states of two black holes look like? Do they contain semiclassical interiors? We approach these questions constructively, providing ensembles of states which densely explore the black hole Hilbert space. The states contain very long Einstein-Rosen (ER) caterpillars: wormholes with large numbers of matter inhomogeneities. Distinguishing these ensembles from the typical entangled states of the black holes is hard. We quantify this by deriving the correspondence between a microscopic notion of quantum randomness and the geometric length of the wormhole. This formalizes a "complexity = geometry'' relation.

Speaker: Martin Sasieta (Brandeis University)

11:20 Coffee break

35 Boundary energy-momentum tensors for asymptotically flat spacetimes

I will discuss the construction of boundary energy-momentum tensors for asymptotically flat spacetimes, which relies on considering the most general allowed conformal Carrollian geometry on future null infinity. I will describe holographic renormalisation of Einstein gravity in such spacetimes, and demonstrate how the variation of the on-shell renormalised Einstein-Hilbert action gives rise to an energy-momentum-news complex in four bulk spacetime dimensions. This complex satisfies a number of Ward identities: the diffeomorphism Ward identity gives rise to covariant Bondi loss equations, while Carroll boosts are anomalous.

Speaker: Emil Have (Niels Bohr Institute)

36 Quasi-topological mass generation for 3D Linearized Gravity

In this talk I will present a new mass generation mechanism for linearized gravity in three spacetime dimensions, which consists of a lower-dimensional Chern-Simons-like term added to the invariant action. The propagators of the gauge fixed massive action show a massive pole and a good massless limit. Moreover, I will show that, as the Topological Massive Gravity model of Deser, Jackiw and Templeton, this theory displays one propagating massive DoF, which can be traced back to the transverse part of the spatial Ricci tensor. Finally, the action of this linearized massive gravity is characterized by an algebraic structure formed by a set of Ward operators, which uniquely determine the theory

Speaker: Erica Bertolini (Dublin Institute for Advanced Studies)

37 Holography for the IKKT matrix model

Holographic dualities that relate type II strings on near-horizon Dp brane geometries to super Yang-Mills theories with sixteen supercharges in p+1 dimensions provide non-conformal generalizations of the famous AdS/CFT correspondence. For the extremal case p=-1, this suggests a holographic duality for the IKKT matrix model -- super Yang-Mills theory reduced to zero dimensions. Despite intriguing and highly non-trivial results in the IKKT model, this duality has remained largely unexplored so far. In this talk, I will consider the lowest supermultiplet of gauge invariant operators of the model and identify its states with the lowest Kaluza-Klein fluctuations of (Euclidean) IIB supergravity on the D(-1) instanton background. I will explain how to construct its holographic bulk realization as a one-dimensional maximal supergravity with 32 supercharges and local SO(10) invariance, capturing the full non-linear dynamics. By analyzing the bulk Killing spinor equations, I will present a general class of half-supersymmetric solutions, which typically break SO(10), and discuss their uplifts to IIB supergravity and, furthermore, to pp-waves in twelve dimensions. These results provide a minimal setup for conducting precision tests of holography involving Einstein gravity.

Speaker: Franz Ciceri (École normale supérieure, Lyon)

13:05 Lunch break

38 GenHET

39 Near-extremal quantum field theories

Near-extremal black holes exhibit universal features such as the near-extremal behaviour of entropy and black hole energy as a function of temperature. These are captured by Jackiw-Teitelboim (JT) gravity in the bulk. Is it possible to see this universality emerging purely from the dual QFT side? We answer this question in the affirmative through three examples of two-dimensional QFTs: 2d CFTs, Warped CFTs, and Carrollian CFTs. We describe the regimes of these theories in which the aforementioned universal behaviour is observed. We compare and contrast it to the universal Cardy regime of these theories and present new results on modular matrices of these theories.

Speaker: Ankit Aggarwal (Vienna University of Technology (TU Wien))

40 Recent developments in AdS3/CFT2 integrability

Although the AdS3/CFT2 duality has been investigated since the early days of holography, it has only been realised in recent years that AdS3/CFT2 is amenable to integrability techniques. This allows for the non-perturbative study of the dynamics of superstrings propagating in different maximally supersymmetric AdS3 backgrounds, allowing information on the dual theories to be extracted. I will present a review talk on the last advancements of integrability methods for the study of this correspondence. This will include the results reviewed in 2312.12930 and the more recent discovery of the S-matrices of AdS3 superstrings supported by a mixture of Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz fluxes: 2306.17553, 2402.11732, 2501.05995.

Speaker: Davide Polvara (University of Hamburg)

41 Gravitational solitons and non-relativistic string theory

We explore the non-relativistic string theory (NRST) limit of type II string theory and its action on gravitational solitons. As a start, we exhibit in detail that the NRST limit is T-dual to a discrete lightcone limit and can be viewed as a near-BPS limit. This also clarifies the nature of multi-string states of NRST and its connection to matrix string theory. We consider the NRST limit of the fundamental string soliton, confirming the recent finding that it corresponds to a relativistic near-horizon background, which we argue is the manifestation of a strong coupling phase of the NRST worldvolume theory. Furthermore, we consider the NRST limit of a class of D-branes as well as the NS5-brane. This reveals that they become gravitational solitons in NRST, as they are sourced torsional string Newton-Cartan (TSNC) geometries. Finally, for the NRST D-brane solitons we show that a further decoupling limit leads to new holographic correspondences between multicritical matrix theories and NRST in curved TSNC backgrounds.

Speaker: Troels Harmark (Niels Bohr Institute)

15:40 Coffee break

42 Higgsing 5d SCFTs - From Geometry, Branes, and Quivers

5d SCFTs can be constructed in String theory via two main approaches. 1) Geometric engineering in M-theory on local Calabi-Yau threefolds (CY3s). 2) As a worldvolume theory on five-brane webs ending on seven-branes in Type IIB String Theory. The possible Higgsings of 5d SCFTs are well understood in the second construction, using branes and so called magnetic quivers. From the geometry side, however, they are much less understood. For 5d SCFTs where both constructions are available, we will show how specific deformations of the CY3 map to turning on moduli for specific branes in the brane web, thus exploring every symplectic leaf in the Higgs branch of the 5d SCFT. This provides a step in understanding the Higgs branch of a 5d SCFT from a purely geometric perspective.

Speaker: Julius Grimminger (University of Oxford)

43 N=2 Chern-Simons-matter theories and Precision Holography

During this talk we will explore the behaviour of the vacuum expectation value of a 1/2-BPS Wilson loop in two broad classes of $\mathcal{N}=2$ Chern-Simons-matter theories beyond leading order. The first class has a dual AdS$_4$ solution in massive type IIA supergravity, while the second class of SCFTs are dual to AdS$_4\times SE_{7}$ solutions in M-theory. The goal of this talk will be to study the holographic counterpart of the Wilson loop operator. In the type IIA limit this is given by the partition function of a fundamental string, while in the M-theory limit its holographic dual is given by the partition function of a probe M2-brane wrapping an M-theory circle direction. Studying these limits will allow us to make a prediction for the sub-leading behaviour of the Wilson loop operator in a large class of Chern-Simons-matter theories, from holography.

Speaker: Alexia Nix (University of Iceland)

44 The importance of being Exact: gauge, integrability, black holes physics and their correspondence

Schroedinger-like equations (Sle) in one dimension have been playing a mayor rôle in modern theoretical physics. In fact, they enter many concrete and even experimental problems in higher dimensions, usually as a reduction, and are suitable for powerful semi-classical analysis since the very beginning of Quantum Mechanics when this method has started shading light on the deep meaning of quantisation. In this respect, one of the most important appearance of Sle equations (of Heun-type, with regular and irregular singularities) occurs, in recent times, in the theory of General Relativity (GR) perturbation by scalars or tensor excitations: with particular relevance for Black Holes (BHs) and their scattering, as they produce ultimately Gravitational Waves. In specific, what matters for theoretical understanding and experimental data is the spectrum of the so-called Quasi Normal Modes (QNMs), the characteristic frequencies of a gravitational object, like a BH. Actually, important is also the computation of the associated wave-functions and Floquet functions, being the latter associated to the Love numbers. A very new method for this investigation has become, more and more, the use of the Nekrasov-Shatashvily partition functions of susy gauge theories. Moreover, it has been shown to be captured by a deep integrability structure encompassing the (direct and inverse) monodromy problem of the Sle. The originality and efficiency of these new powerful idea and method will be described in computing exactly QNMs — via new thermodynamic Bethe Ansatz equations —, the related eigen-functions and the Floquet perturbations. As a byproduct these Sle are produced as limit of the isospectral Painlevé flow to the pole.

Speaker: Davide Fioravanti (INFN and University of Bologna)

17:15 Break

45 Integration on higher-genus Riemann surfaces and string amplitudes

Perturbative calculations in particle physics, gravity and string theory greatly benefit from the spaces of (elliptic) polylogarithm functions which organize iterated integrals on the sphere and the torus. This talk is dedicated to recent generalizations of polylogarithm functions to Riemann surfaces of arbitrary genus. String amplitudes and the Green functions in their conformal-field-theory description are shown to suggest natural building blocks for higher-genus polylogarithms. The resulting function spaces close under integration on the surface and thereby appear suitable for both string-amplitude and Feynman-integral computations. The subject of higher-genus polylogarithms stimulates and draws from rewarding exchange between algebraic geometry and high-energy physics.

Speaker: Oliver Schlotterer (Uppsala University)

46 Conclusion