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## Seminars at

Found at least 20 result(s)

### 22.04.2021 (Thursday)

#### Lattice nonlinear Schroedinger equation: history and open problems.

Journal Club Vladimir Korepin (YITP Stony Brook)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: The model has many names: Lieb-Liniger, Bose gas with delta interaction and nonlinear Schroedinger. A limiting case is called Tonks-Girardeau. It is solvable by algebraic Bethe ansatz. We shall use notations of quantum inverse scattering method. Applications will be mentioned. ----- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed.

### 01.04.2021 (Thursday)

#### Affine Gaudin models and integrable sigma-models

Journal Club Sylvain Lacroix (University of Hamburg)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: In this talk, I will discuss how the formalism of affine Gaudin models can be used to construct new integrable sigma-models. I will start by reviewing the construction of affine Gaudin models and their interpretation as integrable two-dimensional field theories. I will then explain how well-chosen realisations of these models give integrable coupled sigma model on an arbitrary number of copies of a Lie group G^N as well as integrable coset models on the quotient of G^N by a diagonal subgroup. In particular, I will discuss application of the latter construction to T^11 manifolds. --- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.

### 29.03.2021 (Monday)

#### Lonti: A crash course on the superconformal index

Regular Seminar Costis Papageorgakis (QMUL)

 at: 11:15 Otherroom Online abstract: This is the live session included as part of the LonTI lecture on the Superconformal Index. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.

### 25.03.2021 (Thursday)

#### Confining or Not?

Journal Club Igor Klebanov (Princeton University)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: The problem of Color Confinement in Yang-Mills theory is one of the deepest problems in theoretical physics. There is convincing numerical evidence from Lattice Gauge Theory, yet the proof of Confinement in Asymptotically Free theories has not been found. I will briefly introduce the Confinement problem and review some results on large N theories using the gauge/gravity duality. I will then discuss two-dimensional SU(N) theory coupled to an adjoint Majorana fermion. I will show that, when the adjoint mass is sent to zero, the spectrum retains a mass gap but the confinement disappears. Using the Discretized Light-Cone Quantization, I will discuss the spectrum of color singlet states and exhibit certain threshold states. Similar threshold states are also present in a model with a massless adjoint and a massive fundamental fermion. They provide new evidence for the lack of confinement. When the adjoint mass is turned on, the theory becomes confining, and the spectrum of bound states becomes discrete. ---- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com/registration.html. The link will be emailed.

### 22.03.2021 (Monday)

#### Lonti: Entanglement in 1+1D Quantum Field Theory

Regular Seminar Olalla Castro Alvaredo (City)

 at: 11:15 Otherroom online abstract: This is the live session included as part of the LonTI lecture on Entanglement in 1+1D Quantum Field Theory. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D. I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT). The talk will be structured into three main parts: First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields. Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain. Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.

### 22.03.2021 (Monday)

#### Lonti: A crash course on the superconformal index

Regular Seminar Costis Papageorgakis (QMUL)

 at: 10:00 Otherroom Youtube abstract: This recorded tutorial is available via youtube at https://youtu.be/L-C6Xx0uI3c. The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.

### 18.03.2021 (Thursday)

#### TTbar-deformed conformal field theories out of equilibrium

Journal Club Takato Yoshimura (Tokyo Institute of Technology)

 at: 11:00 Otherroom Zoom, instructions in abstract abstract: In this talk I will discuss the universal properties of transport phenomena in TTbar-deformed conformal field theories. TTbar-deformed CFTs are exactly solvable and admit a number of approaches, each of which is seemingly unrelated. Amongst them, for our purpose, which is to study transport phenomena in TTbar-deformed CFTs, we make use of the following: integrability and holography. I will apply these two approaches to study non-equilibrium steady states and Drude weights, finding perfect agreement. I will also discuss a curious connection between TTbar-deformed CFTs and an integrable cellular automaton model called the Rule 54 chain. ------- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.

### 15.03.2021 (Monday)

#### Lonti: Gravity and black holes in AdS

Regular Seminar Toby Wiseman (IC)

 at: 11:15 Otherroom Online abstract: This is the live session included as part of the LonTI lecture on Gravity and black holes in AdS. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.

### 15.03.2021 (Monday)

#### Lonti: Entanglement in 1+1D Quantum Field Theory

Regular Seminar Olalla Castro Alvaredo (City)

 at: 10:00 Otherroom Youtube abstract: This tutorial is available via youtube at https://youtu.be/zU-BRF6xLik. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D. I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT). The talk will be structured into three main parts: First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields. Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain. Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.

### 11.03.2021 (Thursday)

#### Lefschetz thimbles in sigma models

Journal Club Nikita Nekrasov (Stony Brook U., SCGP)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: Two dimensional sigma models describe (harmonic) maps of Riemann surfaces to Riemannian manifolds. I will present the motivations to study the complexification of this problem. I will present the novel approach, developed in my work with Igor Krichever, allowing to construct essentially all twisted complexified harmonic maps of two-torus to spheres and projective spaces. -- Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.

### 08.03.2021 (Monday)

#### Lonti: From spin chain to AdS/CFT with Mathematica

Regular Seminar Nikolay Gromov (KCL)

 at: 12:15 Otherroom Online abstract: This is the live session included as part of the LonTI lecture on "From spin chain to AdS/CFT with Mathematica". Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. â€‹In this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system. Some examples are given with simple Mathematica code. We also discuss applications to AdS/CFT correspondence.

### 08.03.2021 (Monday)

#### Lonti: Gravity and black holes in AdS

Regular Seminar Toby Wiseman (IC)

 at: 10:00 Otherroom Youtube abstract: The release of the youtube video for the London Theory institute seminar series available at https://youtu.be/jtfmWDrC370. Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.

### 04.03.2021 (Thursday)

#### Ten dimensional hidden symmetry of N=4 SYM

Journal Club Frank Coronado (McGill University)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: I will present a generating function for the loop-integrands of all four-point functions of protected single-trace operators in $\mathcal{N}=4$ SYM. This function enjoys a ten-dimensional symmetry that combines spacetime and the internal R-charge symmetries. By considering a 10D light-like limit I will establish a relationship between the simplest four-point correlators (octagons) and four-particle amplitudes. --- Part of the London Integrability Journal Club. If you are a new participant, please register using the form at integrability-london.weebly.com. The link will be emailed.

### 01.03.2021 (Monday)

#### Lonti: From spin chain to AdS/CFT with Mathematica

Regular Seminar Nikolay Gromov (KCL)

 at: 10:30 Otherroom Youtube abstract: The release of the youtube video for the London Theory institute seminar series https://youtu.be/jTRQTwBX9ek. In this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system. Some examples are given with simple Mathematica code. We also discuss applications to AdS/CFT correspondence. Some derivations are formulated in the form of step-by-step exercises. They can be solved either with Mathematica or by hand. A quick introduction to Mathematica is provided in a separate video.

### 25.02.2021 (Thursday)

#### Integrable E-models, 4d Chern-Simons theory and affine Gaudin models

Journal Club Benoit Vicedo (University of York)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: Two-dimensional integrable field theories are characterised by the existence of infinitely many integrals of motion. Recently, two unifying frameworks for describing such theories have emerged, based on four-dimensional Chern-Simons theory in the presence of surface defects and on Gaudin models associated with affine Kac-Moody algebras. I will explain how these formalisms can be used to construct infinite families of two-dimensional integrable field theories. The latter can all naturally be formulated as so-called E-models, a framework for describing Poisson-Lie T-duality in sigma-models. The talk will be based on the joint work [arXiv:2008.01829] with M. Benini and A. Schenkel and [2011.13809] with S. Lacroix. ---- Please register using the form at integrability-london.weebly.com if you are a new participant. The link will be emailed.

### 18.02.2021 (Thursday)

#### Conformal Fourier Analysis and Gaudin Integrability

Journal Club Volker Schomerus (Desy)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: Conformal partial wave expansion provide Fourier-like decompositions of correlation functions in Conformal Field Theory. Despite their fundamental importance, conformal partial waves remain poorly understood, at least beyond the case of four local fields. In the last few years, a deep relation with integrable quantum mechanical models has emerged. It offers a wealth of powerful new algebraic methods to study and construct conformal partial waves e.g. for general supermultiplets, non-local (line-, surface-) operators and multi-point correlation functions. In my talk I will use ideas from harmonic analysis of the conformal group to embed conformal partial waves into the framework of Gaudin integrable models and then discuss several concrete ramifications as trigonometric and elliptic Calogero-Sutherland models. The latter are relevant for multi-point blocks of scalar fields. ----- Part of London Integrability Journal Club. Please register at integrability-london.weebly.com/registration.html if you are a new participant.

### 11.02.2021 (Thursday)

#### Modeling finite-entropy states with free fermions

Journal Club Oleksandr Gamayun (University of Amsterdam)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: The behavior of dynamical correlation functions in one-dimensional quantum systems at zero temperature is now very well understood in terms of linear and non-linear Luttinger models. The "microscopic" justification of these models consists in exactly accounting for the soft-mode excitations around the vacuum state and at most a few high-energy excitations. At finite temperature, or more generically for finite entropy states, this direct approach is not strictly applicable due to the different structure of soft excitations. To address these issues we study the asymptotic behavior of correlation functions in one-dimensional free fermion models. On the one hand, we obtain exact answers in terms of Fredholm determinants. On the other hand, based on "microscopic" numerical resummations, we develop a phenomenological approach that provides results depending only on the state-dependent dressing of the scattering phase. Our main example will be the sine-kernel and correlation functions in XY model. -------------------- Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.

### 04.02.2021 (Thursday)

#### Wilson-'t Hooft lines as transfer matrices

Journal Club Junya Yagi (Tsinghua)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: Supersymmetric gauge theories in four dimensions have various interrelated connections to quantum integrable systems. I will present a new correspondence which identifies Wilson-'t Hooft lines in N=2 circular quiver theories with transfer matrices of trigonometric systems. I will explain how this correspondence is related to Costello's 4d Chern-Simons theory and other similar correspondences. This is based on my joint work with Kazunobu Maruyoshi and Toshihiro Ota. -------------------- Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.

### 28.01.2021 (Thursday)

#### 2D dilaton-gravity, matrix models, and the minimal string

Journal Club Gustavo Turiaci (UC Santa Barbara)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: In the first part of this talk I will review the recent realization that a large class of two-dimensional theories of dilaton-gravity in asymptotically AdS space are holographically dual to a random matrix model. In this description the matrix represents a random boundary Hamiltonian, and its probability distribution depends on the dilaton potential in a specific way. In the second part of the talk I will explain the relation between two-dimensional dilaton-gravity and the minimal string theory. -------------------- Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.

### 21.01.2021 (Thursday)

#### Overlaps and Fermionic Dualities for Integrable Super Spin Chains

Journal Club Charlotte Kristjansen (Niels Bohr Institute Copenhagen)

 at: 15:15 Otherroom Zoom, instructions in abstract abstract: The $\mathfrak{psu}(2,2|4)$ integrable super spin chain underlying the AdS/CFT correspondence has integrable boundary states which describe set-ups where $k$ D3-branes get dissolved in a probe D5-brane. Overlaps between Bethe eigenstates and these boundary states encode the one-point functions of conformal operators and are expressed in terms of the superdeterminant of the Gaudin matrix that in turn depends on the Dynkin diagram of the symmetry algebra. The different possible Dynkin diagrams of super Lie algebras are related via fermionic dualities and we determine how overlap formulae transform under these dualities. As an application we show how to consistently move between overlap formulae obtained for $k=1$ from different Dynkin diagrams. -------------------- Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.