# “Strings, CFT & Integrability”

## Fall Semester 2018

Organised by: Matthias Gaberdiel, Blagoje Oblak, Hagen Münkler

day

date

date

time

venue

venue

speaker

title

title

Thu

16.08.

11:00

HIT E41.1

Kiryl Pakrouski (Princeton)

“Spectrum of O(4)^3 Majorana Tensor Model: SYK-like system without disorder”

Tue

25.09.

11:30

HIT E41.1

Agnese Bissi (Uppsala University)

“Analytic conformal boostrap and its applications”

Wed

03.10.

11:00

HIT E41.1

Piotr Tourkine (CERN)

“New twisted string theories”

abstract (click to view)
Twistor strings have undergone a renewal of interest since the discovery of the Cachazo-He-Yuan formalism for scattering amplitudes in field theory in 2013. These formulae deeply challenge the way we think about scattering amplitudes in quantum field theory and are neatly explained by the so-called ambitwistor string, a cousin of the old twistor string. The existence of these remarkable formalisms, which I shall present to you during the talk, called for a connection to good old string theory. The answer to this question is now understood: it relies on counter-intuitive limits and crucially, the existence of a different quantization for string theory, which we called “twisted strings”. The first part of the talk will be concerned on making that connection to string theory clear. In the second part of the talk, I’ll report on recent results obtained with Eduardo Casali on the winding modes of these twisted strings. They give rise to new exotic target space theories, naively non unitary, but exhibiting features half way between string and field theory. In particular, they are T-duality symmetric. (click to hide)

Wed

10.10.

11:00

HIT E41.1

Rob Klabbers (Humboldt University)

“Holographic correlators finally cracked”

abstract (click to view)
In this talk I will discuss recent advances in the computation of four-point functions of 1/2 BPS operators in N=4 SYM using AdS/CFT. These are the simplest dynamical correlation functions and their study goes back to the early days of AdS/CFT research. Not long ago the proposition of a closed formula in Mellin space for the strong-coupling limit of these four-point functions rekindled interest in them, as further results could disprove or corroborate the conjectured formula. I will discuss how one can compute the strong-coupling limit of these correlation functions using the supergravity action through the AdS/CFT correspondence. I will in particular explain how the algorithm was recently improved to allow for the computation of virtually any correlator of 1/2 BPS operators. Moreover, I will explain how to go from these coordinate space results to Mellin space and back. (click to hide)

Wed

17.10.

11:00

HIT E41.1

Pietro Longhi (ETH Zurich)

“BPS counting in five dimensions with lagrangian defects”

Wed

24.10.

11:00

HIT E41.1

Ruben Monten (CEA Saclay)

“Higher spin quantum gravity in de Sitter space”

Wed

31.10.

11:00

HIT E41.1

Roberto Tateo (INFN Turin)

“TTbar-deformed classical and quantum field theories”

abstract (click to view)
Surprising links between the deformation of 2D quantum field theories induced by the composite $T \bar{T}$ operator, effective string models and the AdS/CFT correspondence, have recently emerged. I will discuss various classical and quantum aspects of this special irrelevant perturbation, including its geometrical interpretation at classical level. (click to hide)

Wed

07.11.

11:00

HIT E41.1

Ben Gripaios (University of Cambridge)

“Topological Actions and Differential Cohomology”

Wed

14.11.

11:00

HIT E41.1

Enrico Brehm (AEI Golm)

“Universal results on matrix elements in CFT from modular covariance”

Tue

20.11.

11:30

HIT E41.1

Falk Hassler (University of Oviedo)

“Poisson-Lie T-Duality in Double Field Theory”

abstract (click to view)
A formulation of Double Field Theory is presented which makes Poisson-Lie T-duality manifest. It allows to identify the doubled space with a Drinfeld double and provides a powerful tool to extract the transformation of the metric, B-field, dilaton and R/R potentials under Poisson-Lie T-duality. Its application to integrable deformations is discussed. (click to hide)

Thu

22.11.

16:00

HIT J 53

Giulio Salvatori (University of Milan)

“Positive geometries for 1-loop Integrands”

abstract (click to view)
In past years we have witnessed remarkable progresses in the computation of scattering amplitudes. On the one hand, these progresses allowed to compute amplitudes that seemed previously intractable. On the other hand, they exposed remarkable mathematical structures, intimately tied to the S-matrix, and which offer non conventional understandings of the latter. An example of these new ideas is the Amplituhedron, a sort of polytope that encodes in the combinatorial structure of its boundaries the analytical properties of the S-matrix for N=4 SYM. Remarkably, similar objects - called generalised Associahedra - have been recently individuated for the much simpler bi-adjoint scalar field theory, up to 1-loop level. The aim of this talk is to give a self-contained introduction to these new developments. First, we will give a review of polytopes and their canonical differential forms. Then we will see how 1-loop integrands can be obtained from the differential form of Associahedra. As an application of this approach, we will discuss a new recursive formula inspired by geometry, which would be difficult to prove - let alone imagine - using standard methods of Quantum Field Theory. (click to hide)

Mon

26.11.

11:30

HIT E41.1

Du Pei (Aarhus University & Caltech)

“6d (1,0) theory, 4-manifolds and topological modular forms”

Wed

28.11.

11:00

HIT E41.1

Benjamin Basso (ENS Paris)

“Continuum limit of fishnet graphs and AdS sigma model”

abstract (click to view)
I will talk about the thermodynamical limit of planar fishnet graphs in 4d. Using techniques developed for studying scaling dimensions of single trace operators in N=4 SYM, I will argue that fishnet graphs are described in the continuum limit by the 2d AdS5 non-linear sigma model. (click to hide)

Wed

05.12.

11:00

HIT E41.1

Fabian Ruehle (University of Oxford)

“SU(3) structure and Calabi-Yau manifolds”

Wed

12.12.

11:00

HIT E41.1

Daniel Medina Rincon (ETH Zurich)

“Holographic Wilson loops: Quantum string corrections”

abstract (click to view)
In the gauge-string correspondence Wilson loops have a known physical description at both sides, making them ideal probes for the duality. Localization has lead to predictions at all orders in the coupling for certain Wilson loop configurations in supersymmetric field theories. String calculations at strong coupling have proved surprisingly difficult and have only been successful at leading order and, in very rare cases, next-to-leading order in perturbation theory. I will present recent progress in the string theory computation of Wilson loops in N=4 and N=2* SYM theories, and their matching with predictions from localization. (click to hide)

Wed

19.12.

11:00

HIT E41.1

Daniele Dorigoni (Durham University)

“Cheshire cat resurgence in supersymmetric QM and QFT”

abstract (click to view)
We start by reviewing some background material on Borel transform and resurgent analysis, emphasising their importance in standard perturbation theory for physical observables. We then specialise our discussion to some simple supersymmetric quantum mechanical model, showing how resurgence can be applied also in the case of a truncating, or even vanishing perturbative expansion in a nice example of what is called Cheshire cat resurgence. We continue with a two-dimensional quantum field theory example studying the prototypical CP^{N-1} model with N=(2,2) supersymmetry. After having computed the two-sphere partition function of this model via susy-localisation we show how Cheshire cat resurgence appears also in this quantum field theory example, allowing us to reconstruct non-perturbative physics even in the case of a truncating perturbative expansion. (click to hide)

last modified: Thu, 20 Dec 2018, 15:02 CET