New Ways to Higher Points

29 Sept 2025, 09:00 → 2 Oct 2025, 18:00 Europe/Zurich

HU Berlin, Campus Adlershof

Burkhard Eden (Humboldt-University Berlin)

Workshop on CFT, integrability, and localisation

We hope to bring together experts and students working in the above fields with the intention to create synergy. There will be talks in the morning and discussion sessions in the afternoon.

The focus is on higher-point functions in N=4 SYM and beyond, e.g. recent developments in Carrollian physics. Further principal topics will be relations between integrability and localisation, and recent advances in related QFT methods.

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I have no e-mail contact for Rugaya Ali Dafalla Ali (Padua),  Subhadeep Rakshit (Sikkim), and Namitha Suresh (Tübingen). 

About on-site participation, posters, menu choices for the dinner, and participation in the excursion I have set up a questionnaire on google docs:

https://docs.google.com/forms/d/e/1FAIpQLScOxcbB74oHa-_Vesi3bU-9WMVlywWg_xH8DlnUII1Cx9rJXQ/viewform?usp=sharing&ouid=104914328997264443662

Please provide feedback!

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Recordings of most of the talks are available at:

https://moodle.hu-berlin.de/course/view.php?id=137217

You will have to sign up for the Moodle "course". The enrolment key is "newWays". Sorry to be slow on this.

Somehow the recording of Gwenael's and Gabriel's talk on Tuesday crashed. Likewise, on Thursday Romain was recorded, but in the second and third session I found no way to start the recording again.

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Thanks to Tobias we have photos, click below! With a bit of fantasy one can recognise everyone.

 

 

 

 

 

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Monday 29 September

Opening

Welcome, outline of the topics, comments on the organisation

Convener: Dr B. Eden

1 Opening remarks

Speaker: Dr Burkhard Eden (Humboldt-University Berlin)

eden_NWTHP.pdf

10:00 Coffee

Field Theory Methods

Conveners: Dr B. Eden, Dr V. Chestnov

2 Algebraic Structures of Higher-Point Amplitudes

Perturbative higher-point scattering amplitudes present both conceptual and computational challenges. Their Feynman integral building blocks rapidly grow in complexity in multi-scale kinematics, motivating the use of new tools from computational algebraic geometry. Viewing these integrals as twisted period integrals further reveals deep connections to the theory of D-modules and modern mathematics. I will illustrate how these algebraic perspectives enrich our understanding of higher-point functions in Quantum Field Theory.

Speaker: Dr V. Chestnov

chestnov_NWTHP.pdf

3 Correlation functions in N=2 superconformal long-quiver theories

In this talk, I will analysis special correlation functions of chiral primary half-BPS operators in four-dimensional N=2 superconformal circular quiver theories. Supersymmetric localization reduces these observables to matrix integrals which, in the planar limit, can be expressed as certain Fredholm determinants, known in this context as generalized Tracy–Widom distribution. This representation provides analytic control over a wide range of parameters, from weak to strong coupling and in various limits involving the number of nodes and operator dimensions. At strong coupling, the standard semi-classical AdS/CFT expansion breaks down in the long-quiver limit. By systematically including perturbative corrections in inverse ’t Hooft coupling together with an infinite tower of nonperturbative, exponentially suppressed terms, we obtain a remarkably simple closed expression for the correlators. The result displays exponential decay with node separation and admits a natural interpretation in terms of a five-dimensional effective theory. In this framework, we extract the spectrum of excitations propagating along the emergent fifth dimension, finding it to be determined by the zeros of Bessel functions.

Speaker: Dr A. Testa

testa_NWTHP.pdf

11:50 Coffee

Break

4 Associators as calculational tools for scattering amplitudes

Speaker: Dr J. Brödel

broedel_NWTHP.pdf

5 Genus-one coactions from zeta generators

The motivic coaction of multiple zeta values and multiple polylogarithms encodes both structural insights on and computational methods for scattering amplitudes in a variety of quantum field theories and in string theory. I will report on work in progress with Franziska Porkert and Oliver Schlotterer where we propose coaction formulae for iterated integrals over holomorphic Eisenstein series that arise from configuration-space integrals at genus one. Our proposal is motivated by formal similarities between the motivic coaction and the single-valued map of multiple polylogarithms at genus zero that are exposed in their recent reformulations via zeta generators. The proposed genus-one coaction is constructed by analogy with the construction of single-valued iterated Eisenstein integrals via zeta generators at genus one and subjected to various checks.

Speaker: Dr A. Kleinschmidt

kleinschmidt_NWTHP.pdf

6 Analytic Evaluation of Feynman Integrals using Mellin-Barnes Representation

Speaker: Dr S. Banik

banik_NWTHP.pdf

14:20 Lunch

Break

7 Discussion

Speaker: NN

Reception

Welcome event with a surprise. Unfortunately there is no way to fund catering. I will provide some wine and cheese or similar and would encourage everyone else to help a bit, too. There are food stores around the institute.

Tuesday 30 September

Localisation and Integrability

Conveners: Prof. A. Lerda, Prof. M. Frau

8 Aspects of localization - matrix models in N=2 , d=4 SYM theories

Speaker: Prof. M. Billo

billo_NWTHP.pdf

10:00 Coffee

Break

9 Exact results and Integrated correlator in 4d N=2 SCFTs

We consider the four-dimensional N=2 superconformal quiver gauge theory
arising from a Z2 orbifold of N=4 super Yang–Mills. Exploiting
supersymmetric localization, we analyze different types of integrated
correlators. In particular, we obtain exact expressions valid in the
large-N limit of the theory for integrated correlators involving two
Coulomb branch operators and two moment map operators, for the
correlator of four moment map operators, and for correlators involving
multiple coincident Wilson lines and two moment map operators. We then
derive the leading terms of their strong-coupling expansions and compare
our results with those of the maximally supersymmetric theory.

Speaker: Dr A. Pini

pini_NWTHP.pdf

10 Exact Three-Point Functions in N=2 Superconformal Field Theories

We propose an integrability approach for planar three-point functions at finite coupling in N=2 superconformal field theories obtained as Z_K orbifolds of N=4 super Yang-Mills (SYM). Generalising the hexagon formalism for N=4 SYM, we reproduce the structure constants of Coulomb branch operators, previously obtained by supersymmetric localisation, as exact functions of the 't Hooft coupling. Our analysis explains the common physical origin of Fredholm kernels in integrability and localisation, and hints at structures after the resummation in the hexagon formalism. This talk is based on arXiv:2503.07295 written with S. Komatsu and D. Serban.

Speaker: Dr G. Ferrando, G. Lefundes

ferrandoLefundes_NWTHP.pdf

11:50 Coffee

Break

11 1/2 BPS Nahm pole defects in N=4 SYM

Speaker: Prof. C. Kristjansen

kristjansen_NWTHP.pdf

12 Correlation Functions of Multiple Light-like Wilson Loops in N=4 SYM

Scattering amplitudes are dual to polygonal light-like Wilson loops in planar N=4 super Yang-Mills theory. Here we will explore the computation of multiple light-like loops and demonstrate that many techniques familiar from the amplitude/single loop case extend to correlators of multiple loops, in particular one may use supertwistor Wilson loops, BCFW recursion and Q-bar equations to facilitate their computation.

Speaker: Prof. J. Drummond

drummond_NWTHP.pdf

13:40 Lunch

Break

13 Discussion

Excursion

The HU campus is situated at the historical Johannisthal airfield from the early days of aviation. We will visit a number of sites related to aviation research.

14 Excursion

The HU Adlershof campus is situated at the historical Johannisthal airfield. We will visit a number of sites from aviation research.

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Wednesday 1 October

Correlators

Conveners: Prof. J. Drummond, Prof. P. Heslop

15 Heavy-Heavy-Light-Light correlators in N=4 SYM

Speaker: Dr C. Wen

wen_NWTHP.pdf

10:00 Coffee

Break

16 A hidden permutation symmetry of squared amplitudes in N=4/ABJM theory

The squared amplitude has emerged as a remarkable object in both planar N=4 SYM and ABJM theory. In N=4, its duality with Wilson loops and correlators implies that the N-point, L-loop squared amplitude is captured by permutation-invariant f-graphs with N+L points. By analyzing the "cusp limit" of the correlator, we establish a new double-triangle graphical rule that bootstraps f-graph coefficients, allowing us to reach up to 16 points. In ABJM, whether such a duality exists is still unknown. We define the squared amplitude in this setting and show that its integrands can also be packaged into a permutation-invariant generating function with N+L points. Remarkably, this object admits two equivalent descriptions—via planar and bipartite f-graphs. Exploiting this property, together with conjectured graphical rules, we bootstrap the generating function up to 10 points. These results strongly suggest the presence of a correlator dual to the squared amplitude in ABJM.

Speaker: Dr C. Shi

shi_NWTHP.pdf

17 Positive Geometry and Leading Singularities in Correlation Functions

The Correlahedron, introduced by Eden, Heslop, and Mason, provides a positive geometric framework for computing correlation functions in maximally supersymmetric Yang–Mills theory. In this talk, I will review the underlying geometry and present recent developments, particularly the introduction of chambers, which partition the space into regions corresponding to distinct physical contributions. This structure leads to a natural representation of the correlator as a sum over leading singularities multiplied by pure functions. Remarkably, the leading singularities reduce to just six basis elements, related by simple permutations—revealing a surprisingly compact and symmetric structure underlying the correlators.

Speaker: Dr C. Kuo

kuo_NWTHP.pdf

11:50 Coffee

Break

18 Correlators with BPS bound states and the double-particle limit of 5pt Amplitudes in AdS5xS5

Speaker: Dr F. Aprile

aprile_NWTHP.pdf

19 Adventures at Five Points

I will consider correlation functions of five scalar BPS
operators in N=4 SYM theory from various perspectives, and
present recent results on their computation.

Speaker: Dr T. Bargheer

bargheer_NWTHP.pdf

20 The AdS4 × CP3 Virasoro-Shapiro Amplitude

I will present the derivation of the AdS Virasoro-Shapiro amplitude for the scattering of gravitons in type IIA string theory on AdS4xCP3. This is achieved by combining the structure of the OPE in the AdS/CFT dual ABJM theory with an ansatz for the amplitude as a string worldsheet integral over single-valued polylogarithms. 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 dimensions of the exchanged massive string operators, some of which have been independently computed using integrability. We also predict the strong coupling dimensions of some operators which have not been previously studied using integrability.

Speaker: Dr T. Hansen

hansen_NWTHP.pdf

14:20 Lunch

Break

21 Discussion

Dinner

Convener: All!

22 Dinner

We dine at Nolle. Nice art nouveau interior in the very heart of Mitte.

The food deal is a small starter (the same for everyone), and a main dish and a desert that you will be able to choose from a restricted menu. Iced water will be supplied. Drinks and - if you want to make them nervous, additional food - are not covered by the conference funding; the rules are unfortunately very restrictive. I do in fact have more money, but helas, I must not invest it ...

A questionnaire about your choice of dishes and some other points should have gone out to you.

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Thursday 2 October

Carrollian Physics, Integrability

Conveners: Prof. C. Kristjansen, Prof. Z. Bajnok

23 Towards a Flat Space Carrollian Hologram from AdS/CFT

Carrollian holography suggests that gravity in (D+1)-dimensional asymptotically flat spacetime is dual to a D-dimensional Carrollian CFT living at null infinity. I will review the current status of flat space holography and explain how this picture arises from the AdS/CFT correspondence. In particular, I will show that taking the flat space limit in the bulk corresponds to a Carrollian limit at the boundary, which allows us to derive explicit examples of flat space holograms.

Speaker: Dr R. Ruzziconi

ruzziconi_NWTHP.pdf

10:00 Coffee

Break

24 High-energy string theory and tensionless strings

Speaker: Dr S. Stieberger

stieberger_NWTHP.pdf

25 Towards a Flat Space Hologram from AdS_4/CFT_3

Speaker: Dr A. Lipstein

lipstein_NWTHP.pdf

11:50 Coffee

Break

26 Relative twisted cohomology in QFT and localization

Speaker: Dr A. Pokraka

pokraka_NWTHP.pdf

27 Dressing factors for mixed-flux AdS3× S3× T4 superstrings

It has been known for some years that strings on AdS3 × S3 × T4 can be described by an integrable family of non-linear sigma models with two free parameters: the string tension and the ratio between Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz fluxes. After fixing a light cone gauge it is possible to describe the worldsheet fluctuations of these strings in terms of particles whose S-matrix can be obtained through the so-called bootstrap approach. This S-matrix is almost entirely fixed through symmetry considerations up to certain scalar functions called dressing factors. These functions are fundamental to understanding the particle content of the theory, comprising both fundamental particles and bound states, and ultimately finding the energy levels of the string through the (Thermodynamic) Bethe Ansatz equations. In this talk I will present recent proposals for the dressing factors of this model, and I will discuss their analytic properties.

Speaker: Dr D. Polvara

polvara_NWTHP.pdf

13:40 Lunch

Break

28 Discussion