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## Seminars at

Found at least 20 result(s)

### 16.07.2020 (Thursday)

#### t.b.a.

Journal Club Sergei Lukyanov (Rutgers)

 at: 15:00 Otherroom Zoom, instructions in abstract abstract: t.b.a. ------------------------ Part of London Integrability Journal Club. New participants please register at integrability-london.weebly.com to receive the link. (Registration is needed only once).

### 15.07.2020 (Wednesday)

#### D0-brane matrix model and holography

Journal Club Masanori Hanada (University of Surrey)

 at: 11:00 Otherroom Virtual abstract: The D0-brane matrix model (the BFSS matrix model and the BMN matrix model) can describe various objects including type IIA black zero-brane, M-theory black hole, M2-branes and M5-branes. We study this theory from several different angles. We put the emphasis on the importance of the dynamics of eigenvalues of matrices, and more generally, color degrees of freedom. Furthermore we explain how the Euclidean theory can be studied by using the Monte Carlo method, and discuss the future directions. If you have a good idea we can test it on computer together! Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for link to the meeting.

### 09.07.2020 (Thursday)

#### Solving the Yang-Baxter equation

Journal Club Marius de Leeuw (Trinity College Dublin)

 at: 15:00 Otherroom Zoom, instructions in abstract abstract: The Yang-Baxter equation is an important equation that appears in many different areas of physics. It signals the presence of integrable structures which appear in topics ranging from condensed matter physics to holography. In this talk I will discuss a new method to find all regular solutions of the Yang-Baxter equation by using the so-called boost automorphism. The main idea behind this method is to use the Hamiltonian rather than the R-matrix as a starting point. I will demonstrate our method by classifying all solutions of the Yang-Baxter equation of eight-vertex type. I will also consider certain 9x9 and 16x16 solutions and give new integrable models in all of these cases. As a further application, I will discuss all integrable deformations of R-matrices that appear in the lower-dimensional cases of the AdS/CFT correspondence. -------------------------- Part of London Integrability Journal Club. New participants please register at integrability-london.weebly.com for the link. (Registration is only needed once).

### 08.07.2020 (Wednesday)

#### Remarks on the complex SYK model

Journal Club Grigory Tarnopolsky (Harvard)

 at: 15:00 Otherroom Virtual abstract: In this talk I will discuss new properties of the complex SYK model in comparison with the Majorana one. I’ll mostly focus on spectrum of operators and the effective low energy action of the complex SYK model. In this case the conserved U(1) charge contributes a compact scalar field to the effective action in addition to the Schwarzian term. Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for link to the meeting.

### 25.06.2020 (Thursday)

#### Exact g-functions

Journal Club Joao Caetano (Simons Center)

 at: 15:00 Otherroom Zoom, instructions in abstract abstract: The g-function is a measure of degrees of freedom associated to a boundary of two-dimensional quantum field theories. In integrable theories, it can be computed exactly in a form of the Fredholm determinant, but it is often hard to evaluate numerically. In this paper, we derive functional equations---or equivalently integral equations of the thermodynamic Bethe ansatz (TBA) type---which directly compute the g-function in the simplest integrable theory; the sinh-Gordon theory at the self-dual point. The derivation is based on the classic result by Tracy and Widom on the relation between Fredholm determinants and TBA, which was used also in the context of topological string. As a side result, we present multiple integrals of Q-functions which we conjecture to describe a universal part of the g-function, and discuss its implication to integrable spin chains. ------------------------- Part of London Integrability Journal Club. New participants please register at integrability-london.weebly.com to receive the link.

### 24.06.2020 (Wednesday)

#### A review of SYK and attempts at a bulk dual

 at: 15:00 Otherroom Virtual abstract: Most recent discussions of holography in AdS_2/CFT_1 have focused on the Schwarzian and JT gravity. However, the AdS dual of SYK is expected to, in addition, contain an infinite tower of massive fields. The interactions for these fields are in principle fixed by the SYK correlation functions. We review the construction of all-point correlation functions in SYK. We comment on the difficulties in finding a coherent description of the bulk tower of fields. Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for link to the meeting.

### 17.06.2020 (Wednesday)

#### A new observable to decode emergent gravity

Journal Club Josephine Suh (Caltech)

 at: 17:00 Otherroom Virtual abstract: I review the emergence of JT gravity from the SYK model, and the calculation of correlation functions in JT gravity. I motivate the need for a new observable distinct from entanglement entropy to fully decode emergent gravity, and propose as such an observable a quantum generalization of the entropy of multiple measurements on a dynamical system. Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for link to the meeting.

### 12.06.2020 (Friday)

#### Discussion about replica wormholes and ensembles

Journal Club Douglas Stanford (Stanford)

 at: 16:30 Otherroom Virtual abstract: The goal is to have a general discussion about replica wormholes and the black hole information problem. To start things off, we will discuss the question of whether an ensemble interpretation is necessary for the replica wormhole computations of the entropy. Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for link to the meeting. NOTE THAT THE TIME/DATE OF THE TALK HAS BEEN CHANGED.

### 11.06.2020 (Thursday)

#### Fishnet CFT: TBA and Non-compact Spin Chain

Journal Club Gwenael Ferrando (ENS Paris)

 at: 15:00 Otherroom online, instructions in abstract abstract: The fishnet CFT is a non-unitary CFT of two matrix complex scalar fields interacting via a single quartic potential. The chiral nature of the interaction strongly constrains the Feynman diagrams arising at each order in perturbation theory, those that survive are of fishnet type. In this talk, I will present the TBA equations for the conformal dimensions of multi-magnon local operators in this theory. I will emphasize the need to diagonalize suitable graph-building operators in order to determine the asymptotic data, dispersion relation and S matrix, on which the TBA relies. A dual version of the TBA equations, relating D-dimensional graphs to two-dimensional sigma models, will also be examined. The last part of the talk will be devoted to the presentation of the underlying non-compact spin chain and of additional results regarding diagonalization of graph-building operators. --------------------- Part of London Integrability Journal Club. New participants please register at integrability-london.weebly.com for the link.

### 04.06.2020 (Thursday)

#### Crossing equations for mixed flux AdS3/CFT2 (UNUSUAL TIME)

Journal Club Olof Ohlsson Sax (NORDITA)

 at: 15:00 Otherroom Zoom, instructions in abstract abstract: I will give an overview of recent progress in understanding string theory in AdS3 backgrounds with a mixture of Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz three-form flux. Such theories are integrable, but provide many features not encountered in the more familiar case of pure Ramond-Ramond flux. In this talk I will explore the analytic structure of the dispersion relation of the world-sheet excitations and how it relates to the crossing equations of the two-particle S matrix. Determining the dressing phases of the mixed flux S matrix is the next major step in using integrability to the AdS3/CFT2 correspondence. -------- Part of London Integrability Journal Club. New participants please register at integrability-london.weebly.com to receive the link.

### 03.06.2020 (Wednesday)

#### From bulk reconstruction to Berry phases and back

Journal Club Bartlomiej Czech (IAS, Tsinghua U.)

 at: 15:00 Otherroom Virtual abstract: The first half of the talk will be a review of the main ingredients of bulk reconstruction: the Ryu-Takayanagi formula and subregion duality, the JLMS theorem, error correction and the complexity conjecture. The second half will be about my recent and current work on "modular Berry phases"--a type of Berry phase which characterizes the entanglement structure of a quantum state. We will see that the bulk curvature in AdS is (up to an integral transform) a special case of the modular Berry phase, though the concept has many other applications which we may or may not discuss. Part of the Black Hole Information Paradox Journal Club. Please email damian.galante@kcl.ac.uk for Zoom link to the meeting.

### 28.05.2020 (Thursday)

#### Boundary states, overlaps, nesting and bootstrapping AdS/dCFT

Journal Club Tamas Gombor (Wigner Research Center, Budapest)

 at: 14:00 Otherroom Zoom, instructions in abstract abstract: Recently there have been renewed interest and relevant progress in calculating overlaps between periodic multiparticle states and integrable boundary states. They appear in quite distinct parts of theoretical physics including statistical physics and the gauge/string duality. I will give a summary of known overlap formulas and analyze the connection between selection rules and symmetries. I will introduce a nesting procedure for boundary states which provides the factorizing overlaps for higher rank algebras automatically. This method can be used for the calculation of the asymptotic all-loop 1-point functions in AdS/dCFT. In doing so I will present the solutions of the YBE for the K-matrices with centrally extended su(2|2) symmetry and the generic overlaps of the corresponding boundary states. Based on 2004.11329 ------------------------- Part of London Integrability Journal Club. Please register at integrability-london.weebly.com/ for the zoom link

### 21.05.2020 (Thursday)

#### Integrable Field Theories with an Interacting Massless Sector

Journal Club Ines Aniceto (University of Southampton)

 at: 14:00 Otherroom Zoom, instructions in abstract abstract: Integrability techniques have played a major role in the study the AdS/CFT correspondence, providing an accurate description of different string theoretic observables beyond the weak or strong coupling perturbation theory. However, the case of string on certain AdS_3 backgrounds provided new challenges in the form of massless excitations. Difficulties in incorporating these into the integrable description have led to disagreements concerning the energy of massive physical states. In general integrable theories, massless and massive sectors can generally be treated separately. We know this cannot be the case in AdS_3, but a full TBA description of the interaction between the sectors is yet to be found. Surprisingly, such a description can found in a family of integrable field theories — homogeneous sine-Gordon models. Here, one can take a double scaling limit of the adjustable parameters and zoom into a regime described by a TBA where the massless sector does not decouple and contributes to the energy of massive particles at the same order as for which the Bethe ansatz would suffice in a massive theory. ------- Part of London Integrability Journal Club. Please register at integrability-london.weebly.com for the link.

### 15.05.2020 (Friday)

#### Wilson loops as Matrix Product States (NOTE UNUSUAL TIME AND DAY)

Journal Club Shota Komatsu (IAS)

 at: 14:00 Otherroom Zoom, instructions in abstract abstract: In his paper in 1979, Polyakov envisaged a possibility of reformulating the gauge theory as a Principal Chiral Model defined on a space of loops and discussed "the loop-space integrability". This idea, together with a closely related idea of the loop equation, led to numerous important results in matrix models and 2d gauge theories, but its application to four-dimensional gauge theories had only limited success. Now, after 50 years, we have a concrete example of integrable four-dimensional gauge theory, N=4 SYM. However integrability in N=4 SYM is formulated mostly in terms of local operators, although important progress has been made in constructing the Yangian for the Wilson loops. In this talk, I will present a framework which would bridge these two distant notions of integrabililty. The key player in the story is a correlation function of a local operator and the Wilson loop. I reformulate the gauge-theory computation of this observable as an overlap between an energy eigenstate of a spin chain and a matrix product state (MPS). Unlike standard MPS's discussed in the literature, our MPS has infinite bond dimensions in order to accommodate infinite dimensionality of the space of loops. It provides an "intertwiner" between integrable structures of the local operators and the Wilson loops, and in particular implies the existence of a special set of deformations of the Wilson loop which satisfy the QQ-relation. I will also explain how to formulate a nonperturbative bootstrap program based on the results obtained in this framework and compute the correlator of the circular BPS Wilson loop and general non-BPS operators at finite coupling, emphasizing the relation to and the difference from other observables that were computed by a similar approach. ----------------- Part of London Integrability Journal Club. Please register using the form at integrability-london.weebly.com

### 07.05.2020 (Thursday)

#### Completeness of Bethe equations

Journal Club Dmytro Volin (Uppsala University)

 at: 10:00 Otherroom Zoom, instructions in abstract abstract: We review a proof of bijection between eigenstates of the Bethe algebra and solutions of Bethe equations written as a Wronskian quantisation condition or as QQ-relations on Young diagrams. Furthermore, it is demonstrated that the Bethe algebra is maximal commutative and it has simple spectrum every time it is diagonalisable. The proof covers rational gl(m|n) spin chains in the defining representation with the famous Heisenberg spin chain being a particular subcase. The proof is rigorous (no general position arguments are used). We do not rely on the string hypothesis and moreover we conjecture a precise meaning of Bethe strings as a consequence of the proposed proof. A short introduction with necessary facts about polynomial rings will be given at the beginning of the talk. Based on 2004.02865 NOTE: Part of London Integrability Journal Club. Please register at integrability-london.weebly.com to participate.

### 06.05.2020 (Wednesday)

#### A personal bird eye view of fuzzballs

Journal Club Rodolfo Russo (QMUL)

 at: 15:00 Otherroom Virtual abstract: There are indications that "traditional" GR physics at the horizon and usual assumptions of locality cannot provide a consistent description of black holes. The fuzzball paradigm suggests that "traditional" GR physics at the horizon should be relaxed and that string theory provides the right degrees of freedom to have a non-trivial structure at the scale of the horizon. I'll review how this idea has emerged from the analysis of the Strominger-Vafa black hole and its implication for the AdS3/CFT2 duality. For link to the meeting, please email damian.galante@kcl.ac.uk.

### 30.04.2020 (Thursday)

#### Computing scalar products in the Bethe Ansatz

Journal Club Juan Miguel Nieto Garcia (University of Surrey)

 at: 10:00 Otherroom Zoom, instructions in abstract abstract: Computing scalar products is a non-trivial problem in the context of the Algebraic Bethe Ansatz. In this talk I comment about the different problems one encounter and how to easily compute recurrence relations for scalar products, even beyond SU(2). I will also present a possible explanation for the existence of determinant representations of the scalar products. NOTE: Part of London Integrability Journal Club. Please register at integrability-london.weebly.com

### 23.04.2020 (Thursday)

#### Exact results with defects: an overview

Journal Club Lorenzo Bianchi (QMUL)

 at: 10:00 Otherroom Zoom, instructions in abstract abstract: I will give a summary of recent progress in the computation of exact results in the presence of superconformal defects, focusing on a special class of defect correlators. Along the way, I will comment on the possibility of using integrability and propose various future directions. NOTE: to receive the link please fill the registration form at integrability-london.weebly.com

### 22.04.2020 (Wednesday)

#### A status report on the island formula from the perspective of 2d CFT at large central charge

Journal Club Tarek Anous (University of Amsterdam)

 at: 15:00 Otherroom Virtual abstract: I will give an informal review of some of the recent developments on reproducing the page curve in semi-classical gravity. I will then compare and contrast these results to older results from the study of holographic 2d CFT with sparse spectra and large central charge. In these quantum systems, there is a natural understanding of the CFT duals of the bulk semiclassical classical saddles that are responsible for evading information loss. I will end with some cautionary remarks explaining why I believe it is too early to declare the information problem "solved". For Zoom link please contact damian.galante at kcl.ac.uk

### 16.04.2020 (Thursday)

#### A review of the AdS/CFT Quantum Spectral Curve

Journal Club Fedor Levkovich-Maslyuk (ENS Paris)

 at: 10:00 Otherroom online seminar abstract: I will give an introduction to the Quantum Spectral Curve in AdS/CFT. This is an integrability-based framework which provides the exact spectrum of planar N = 4 super Yang-Mills theory (and of the dual string model) in terms of a solution of a Riemann-Hilbert problem for a finite set of functions. I review the underlying QQ-relations starting from simple spin chain examples, and describe the special features arising for AdS/CFT. I will also present some pedagogical examples to show the framework in action. Lastly I will briefly discuss its recent applications for correlation functions. Based on the review arXiv:1911.13065. NOTE: online seminar using Zoom. Please register to the mailing list on integrability-london.weebly.com to participate.