# “Strings, CFT & Integrability”

## Spring Semester 2017

Organised by: Niklas Beisert, Matthias Gaberdiel, Mahdi Godazgar, Christoph Keller and Blagoje Oblak

day

date

date

time

venue

venue

speaker

title

title

Thu

23.02.

Wellington Galleas (ETH Zürich)

Talks in Mathematical Physics: “Partition function of the elliptic gl₂ SoS model as a single determinant”

abstract (click to view)
Partition functions of vertex models with domain-wall boundaries have appeared in a variety of contexts ranging from enumerative combinatorics to the study of gauge theories. The six-vertex model is the prototype model where such boundary conditions were adopted and, in that case, the model's partition function admits a compact representation in terms of a single determinant. Such representation has led to a number of developments in the field but seemed to be restricted to the six-vertex model. The next natural candidate for this study is the elliptic gl₂ Solid-on-Solid (SoS) model but, despite all efforts, the results suggested single determinantal representations did not exist. This problem has only been recently solved with the help of special functional equations originating from the dynamical version of the Yang-Baxter algebra. In this talk I will discuss this problem and show how families of single determinantal representations for the elliptic SoS model's partition function can be derived in a constructive manner. (click to hide)

Wed

01.03.

14:00

HIT J 53

Monica Guica (CEA Saclay)

“Towards a background-independent construction of the bulk field in AdS₃”

Wed

08.03.

14:00

HIT E41.1

Pietro Longhi (Uppsala university)

“Wall crossing invariants from spectral networks”

abstract (click to view)
In presence of defects the Hilbert space of a quantum field theory can change in interesting ways. Surface defects in 4d N=2 theories introduce a class of 2d-4d BPS states, which the original 4d theory does not possess. For theories of class S, spectral networks count 2d-4d BPS states, and through the 2d-4d wall-crossing phenomenon the 4d BPS spectrum can be obtained. Adopting this physical viewpoint on spectral networks, I will illustrate some recent and ongoing developments based on this framework, with applications to the study of 4d N=2 BPS monodromies and their relations to specialisations of the superconformal index. (click to hide)

Wed

15.03.

14:00

HIT E41.1

Jens Hoppe (KTH Stockholm)

“Quantized Minimal Surfaces”

abstract (click to view)
Concerns solutions of the equation [Xₖ,[Xₖ,Xₘ]]=0 (click to hide)

Wed

22.03.

14:00

HIT E41.1

Jacob Bourjaily (Niels Bohr Institute)

“Stratifying On-Shell Cluster Varieties”

abstract (click to view)
There exists a deep correspondence between a class of physically important functions—called "on-shell functions"—and certain (cluster variety) subspaces of Grassmannian manifolds, endowed with a volume form that is left invariant under cluster coordinate transformations. These are called "on-shell varieties" (which may or may not include all cluster varieties). It is easy to prove that the number of on-shell varieties is finite, from which it follows that the same is true for on-shell functions. This is powerful and surprising for physics, because these on-shell functions encode complete information about perturbative quantum field theory.

In this talk, I describe the details of this correspondence and how it is constructed and give the broad physics motivations for obtaining a more systematic understanding of on-shell cluster varieties. I outline a general, brute-force strategy for classifying these spaces; and describe the results found by applying this strategy to the case of Gr(3,6). (click to hide)

In this talk, I describe the details of this correspondence and how it is constructed and give the broad physics motivations for obtaining a more systematic understanding of on-shell cluster varieties. I outline a general, brute-force strategy for classifying these spaces; and describe the results found by applying this strategy to the case of Gr(3,6). (click to hide)

Wed

29.03.

14:00

HIT E41.1

Marc Magro (ENS Lyon)

“The twist function of an integrable sigma-model”

abstract (click to view)
I shall review the relevance of the twist function for a whole family of integrable sigma-models. In particular, I will show how this function is related to the computation of both local and non-local conserved charges. (click to hide)

Wed

05.04.

14:00

HIT E41.1

Ali Seraj (IPM Tehran)

“Multipole charges in electrodynamics and the vacuum moduli space”

abstract (click to view)
We introduce multipole charges as the Noether charges associated with a subclass of gauge symmetries of Maxwell theory. We show that in a static configuration, these charges are proportional to the electric multipole moments which uniquely specify the system. Moreover, the conservation laws impose infinite number of constraints over the radiation in electrodynamics. The presence of multipole symmetries implies that the vacuum of gauge theory is not unique, but instead an infinite dimensional moduli space, the adiabatic motion on which generates well known solutions of the theory. (click to hide)

Wed

12.04.

14:00

HIT E41.1

James Bonifacio (University of Oxford)

“Constructing and constraining massive spin-2 scattering amplitudes”

abstract (click to view)
I will first review a procedure for constructing tree-level scattering amplitudes for spinning particles. Considering the case of a self-interacting massive spin-2 particle, I show that the four-point amplitudes with the highest cutoff correspond to the known ghost-free massive gravity theories, even allowing for arbitrary derivative interactions and parity-odd terms. This demonstrates that $\Lambda_3$ is a model-independent bound on the strong coupling scale in effective theories of a self-interacting massive spin-2 field. I also remark on possible generalisations to higher spins and additional fields. Lastly, I will discuss how the scattering amplitudes of massive spin-2 theories are constrained by analytic dispersion relations, assuming the existence of a UV-completion that satisfies the usual S-matrix analyticity conditions. (click to hide)

Wed

26.04.

14:00

HIT E41.1

Hjalmar Rosengren (Chalmers university)

“Combinatorics of elliptic lattice models”

Wed

03.05.

14:00

HIT E41.1

Michal Heller (AEI, Potsdam)

“Towards complexity for QFT states: a cMERA study”

Wed

10.05.

14:00

HIT E41.1

Petr Horava (UC Berkeley)

“Nonrelativistic Naturalness, Aristotelian Spacetime and the Higgs Mass Hierarchy”

Wed

24.05.

14:00

HIT E41.1

Prem Kumar (University of Swansea)

“Scrambling time and Lyapunov exponent for higher spin perturbations”

Wed

14.06.

14:00

HIT E41.1

Didina Serban (CEA Saclay)

“Correlation functions from integrability”

abstract (click to view)
The talk will review the computation of the three point function of gauge-invariant operators in the

planar N=4 SYM theory using integrability-based methods.

The structure constant can be decomposed, as proposed by Basso, Komatsu and Vieira, in terms of two hexagons, which can be understood as form factors of twist fields introducing a curvature defect. One of the main challenges in this approach is to perform the sum over virtual particles emitted and absorbed by the hexagons in different channels. I will discuss a method to perform these sums, the contributions currently accessible, the comparison with the results obtained by semiclassics. (click to hide)

planar N=4 SYM theory using integrability-based methods.

The structure constant can be decomposed, as proposed by Basso, Komatsu and Vieira, in terms of two hexagons, which can be understood as form factors of twist fields introducing a curvature defect. One of the main challenges in this approach is to perform the sum over virtual particles emitted and absorbed by the hexagons in different channels. I will discuss a method to perform these sums, the contributions currently accessible, the comparison with the results obtained by semiclassics. (click to hide)

last modified: Fri, 14 Jul 2017, 14:55 CEST