“QFT, Strings and Beyond” – Autumn Semester 2024

Wed

25.09.

15:00

HIT E41.1

Julius Julius (Harish-Chandra Research Institute and ENS Paris)

“Unmixing sub-leading Regge trajectories of N=4 Super-Yang-Mills”

abstract (click to view) This talk is based on arXiv:2409.07529 (https://arxiv.org/abs/2409.07529). We will study the conformal field theory data (CFT-data) of planar 4D N=4 Super-Yang-Mills theory in the strong 't Hooft coupling limit. This regime explores the physics of massive short strings in the flat-space limit of the dual AdS. We focus on the CFT-data of the massive short strings exchanged in the operator product expansion (OPE) of the four-point function dual to the Virasoro-Shapiro amplitude. This CFT-data arranges itself into Regge trajectories in the flat-space limit. Using inputs from recent advances in the computation of the AdS Virasoro-Shapiro amplitude, integrability, and a stipulation based on analyticity of the CFT-data in spin, we are able to fix all the CFT-data on the four unique sub-leading Regge trajectories, at leading non-trivial order, as a function of the string-mass level. One of our predictions is that one of the four unique sub-leading Regge trajectories decouples from the OPE in the flat-space limit. This hints at an emergent selection rule in the flat-space limit, similar to our previous results in arXiv:2310.06041 (https://arxiv.org/abs/2310.06041). Our procedure should be applicable in a variety of similar setups like for the AdS Veneziano amplitude or in ABJM. (click to hide)

Wed

02.10.

15:00

HIT E41.1

Andrea Guerrieri (CERN)

“Bootstrapping non-perturbative gravity amplitudes”

abstract (click to view) The goal of the S-matrix Bootstrap program is to use the full power of the
constraints of causality, crossing, and unitarity to explore the space of
physical non-perturbative scattering amplitudes. In this talk, I will
review the Bootstrap of graviton scattering amplitudes in maximally
supersymmetric theories in dimensions greater or equal than nine in
and https://arxiv.org/abs/2212.00151. In
doing so, I will discuss the numerical setup, and show the numerical
results obtained, providing evidence for the uniqueness of String Theory. I
will conclude by discussing some preliminary results showing how the
numerical data collected from the Bootstrap are in agreement with the
conjectured asymptotic behaviour of non-perturbative gravity amplitudes. (click to hide)

Wed

09.10.

15:00

HIT E41.1

Jan Troost (ENS Paris)

“Topological Symmetric Orbifolds and String Theories”

abstract (click to view) We compute correlators in topological symmetric orbifolds with gauge group S_N, exactly as well as in a large N expansion. These results prove and refine conjectures about extremal correlators. We argue that their string theoretic interpretation requires a grand canonical perspective which in turn clarifies the identification of string vertex operators. (click to hide)

Wed

16.10.

15:00

HIT E41.1

Barak Gabai (EPFL Lausanne)

“Universal Integrated Constraints for Conformal Defects”

Wed

23.10.

15:00

HIT E41.1

Maximilian Schwick (U. of Geneva)

“Resurgence: Theory and Practice”

abstract (click to view) I will start by giving a pedagogical introduction to resurgence methods, using a minimal example. I will introduce Borel-Laplace summation and highlight its connection to Stokes phenomena, which are mediated by Borel plane singularities. The mechanism that organizes these singularities and makes them tractable is called resurgence.
Thereafter I will apply resurgent methods to Seiberg-Witten theory, based on recent work with Marcos Marino. (click to hide)

Wed

30.10.

15:00

HIT E41.1

Denis Karateev (U. of Geneva)

“Correlation Functions and Trace Anomalies in Weakly Relevant Flows”

abstract (click to view) I will discuss abstract weakly relevant flows in a general number of dimensions, which arguably provide the simplest example of a renormalization group (RG) flow between two non-trivial fixed points. I will compute several two-point correlation functions in position space valid along the whole RG flow. I will then focus on four dimensions and compute the change of the a- and c-trace anomalies along the flow in this theory. (click to hide)

Wed

06.11.

15:00

HIT E41.1

Ilia Gaiur (U. of Geneva)

“Higher Bessel Product Formulas”

abstract (click to view) Higher Bessel functions are the solutions to the quantum differential
equations for $\mathbb{P}^{N-1}$. These functions are connected to the
periods of the Dwork families via the Laplace transform, and the functions
themselves are exponential integrals. In my talk, I will show how product
formulas for these irregular special functions lead to other geometric
differential equations associated with higher-dimensional families of
algebraic varieties. I will discuss the geometric and algebraic properties
of the periods for these families and later provide further perspectives on
these correspondences.
Work in collaboration with V.Rubtsov and D. van Straten. (click to hide)

Wed

13.11.

15:00

HIT E41.1

Sebastian Pögel (PSI Villigen)

“Tackling Apparent Singularities in Calabi-Yau Feynman Integrals: An Integral for 5PM Black Hole Scattering”

abstract (click to view) It is well-known that Calabi-Yau geometries make a prominent appearance in the evaluation of a certain class of Feynman integrals. In this talk, I will review properties of such integrals, explore their associated geometry, and discuss current techniques for their evaluation as an expansion in the dimensional regularization parameter. Going beyond the simplest cases of Calabi-Yau integrals—the Banana integrals—I will examine features that require extensions of established methods, notably the the presence of apparent singularities. I will illustrate these methods through the derivation of an epsilon-factorized differential equation for a specific four-loop integral appearing for the 5PM correction to black hole scattering, which is linked to a Calabi-Yau 3-fold geometry. (click to hide)

Thu

14.11.

12:15

HIT E41.1

Albrecht Klemm (U. Bonn)

“High precision black hole scattering and iterated integrals of Calabi-Yau periods”

abstract (click to view) We explore the functions classes that generalize the multiple polylogarithms occuring in one loop evaluations of Feynman integrals in higher loop calculations. The latter involves iterated integrals of Calabi-Yau n-fold periods. Concretely the deflection angle and the radiative loss in the fifth order post Newtonian approximation of black hole scattering are calculated in terms of K3 and Calabi-Yau threefold periods and their iterated integrals. This is one of
the first examples in which these higher algebra-geometric structures determine
physical observables. (click to hide)

Wed

20.11.

15:00

HIT E41.1

Simon Ekhammar (King's College London)

“Asymptotic Baxter-Bethe Ansatz for Regge Trajectories”

abstract (click to view) Maximally supersymmetric four-dimensional Yang-Mills appear to be
solvable in the planar limit. In particular, the spectrum can be described
using the integrability-based Quantum Spectral Curve (QSC) formalism. While
the QSC was originally introduced to study local operators I will explain
how it can also be applied to horizontal Regge trajectories. I will focus
on the weak coupling limit where the QSC simplifies dramatically and can be
recast as a novel "Asymptotic Baxter-Bethe Ansatz": a set of equations
reminiscent of the Beisert-Eden-Staudacher equations. (click to hide)

Wed

27.11.

15:00

HIT E41.1

Nathan McStay (Cambridge U.)

“Twistors and the tensionless limit”

abstract (click to view) The tensionless limit of string theory on AdS3 x S3 x T4 has provided an explicit, proven example of the AdS/CFT correspondence. In this talk, I will discuss the connections between this string theory and twistor theory, elucidating on the target space interpretation in the tensionless limit. I will discuss how incidence relations can be constructed, presenting a map between twistor space and spacetime. This will allow us to explicitly see how bulk information is encoded in the boundary theory. Namely, we will see how states inserted at the boundary can be used to recover the bulk-boundary propagator. Along the way, I will provide a brief introduction to some of the key concepts in twistor theory and explain their relevance to the AdS/CFT correspondence. This talk is based on 2411.08836 in collaboration with Ron Reid-Edwards. (click to hide)

Wed

04.12.

15:00

HIT E41.1

Ana Lúcia Retore (Durham U.)

“Perturbative Yang-Baxter integrability in isotropic spin chains”

abstract (click to view) The presence of Yang-Baxter integrability in a given model provides a series of powerful tools to study its spectrum and properties. This is the case, for instance, in a series of discrete models called integrable spin chains. Examples include the Hubbard model, the Potts model and the Heisenberg spin chain. For most systems of this type, a particle in a given site of the chain only interacts with the ones in its first neighbour sites; they are called Nearest-Neighbour spin chains. Certain applications in gauge theories and statistical physics, however, require understanding long-range deformations.
In this talk, I will start with an introduction to the Yang-Baxter equation and integrable spin chains. I will then present a procedure to include long-range interactions such that integrability is perturbatively preserved at each order. I will show two examples: the spin-1/2 and the spin-1 isotropic chains, and discuss their properties. (click to hide)

Wed

11.12.

15:00

HIT E41.1

Brandon Rayhaun (YITP Stony Brook)

“On Symmetries, Boundaries, and Entanglement Entropy”

abstract (click to view) How do generalized symmetries act on junction operators which
sit at the intersection of a collection of boundaries and interfaces? I
will discuss the answer to this question in the context of 1+1d QFTs. The
presentation will be organized around the derivation of a symmetry-resolved
version of the Affleck-Ludwig-Cardy formula which controls the asymptotic
density of open string states within individual charge sectors, and also
has applications to entanglement entropy. (click to hide)