## Directions

We are located at the 6th floor of the G.O. Jones Building on the Mile End Campus, midway between Stepney Green and Mile End Tube stations, approximately 15-20 minutes from central London on the Central or District lines. If exiting Stepney Green tube station, turn left and walk along the Mile End Road for approximately 300 metres. The G.O. Jones (Physics) building is to the right of the main college building, which is fronted by a clocktower and lawn. If exiting Mile End tube station, turn left and walk approximately 300 metres until you are opposite the main college building. A more detailed description can be found here.

## Seminars at Queen Mary University of London

Found at least 20 result(s)

### 03.12.2020 (Thursday)

#### Topologically Ordered Matter and Why You Should be Interested

Regular Seminar Steven Simon (Oxford)

 at: 14:00 QMWroom zoom abstract: Abstract: In two dimensional topologically ordered matter, processes depend on gross topology rather than detailed geometry. Thinking in 2+1 dimensions, particle world lines can be interpreted as knots or links, and the amplitude for certain processes becomes a topological invariant of that link. While sounding rather exotic, we believe that such phases of matter not only exist, but have actually been observed in quantum Hall experiments, and could provide a route to building a quantum computer. Possibilities have also been proposed for creating similar physics in systems ranging from superfluid helium to topological superconductors to semiconductor-superconductor junctions to quantum wires to spin systems to graphene to cold atoms. Please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk for the zoom link.

### 26.11.2020 (Thursday)

Regular Seminar Paul Heslop (Durham University)

 at: 14:00 QMWroom Zoom abstract: For zoom link please email s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13:30. Abstract: I will discuss 2 recent results arising out of the recent resurgence in concrete tests / predictions of AdS/CFT over the last few years. The first is the precise identification of the CFT operators dual to single particle supergravity states (based on 2007.095395) and the second is a forthcoming work explicitly relating four-point correlators to a string effective action on AdSxS.

### 23.11.2020 (Monday)

#### Lonti 2020:Witten diagrams and the Mellin transform in AdS/CFT

Regular Seminar Congkao Wen (QMUL)

 at: 10:30 QMWroom Online abstract: This is the live session included as part of the LonTI lecture on Witten diagrams and the Mellin transform in AdS/CFT. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.

### 19.11.2020 (Thursday)

#### Cutkosky Rules and Unitarity (Violation) in D-instanton Amplitudes

Regular Seminar Ashoke Sen (Harish-Chandra Research Institute)

 at: 14:00 QMWroom Zoom abstract: In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the proof of unitarity is somewhat different; we need to sum over only those cut diagrams for which all the world-sheet boundaries ending on some particular D instanton lie on the same side of the cut. By working with the closed string effective action, obtained after integrating out the open string modes, we prove that the D-instanton amplitudes actually satisfy these cutting rules, provided the effective action is real. The violation of unitarity in the closed string sector of two dimensional string theory can be traced to the failure of this reality condition. In the critical superstring theory, multi-instanton and multi anti-instanton amplitudes satisfy the reality condition. Contribution to the amplitudes from the instanton anti-instanton sector satisfies the reality condition if we make a specific choice of integration cycle over the configuration space of string fields, whereas contribution due to the non-BPS D-instantons will need to either vanish or have an overall real normalization in order for it to give real contribution. (please email jung-wook.kim AT qmul.ac.uk for the zoom link)

### 12.11.2020 (Thursday)

#### Celestial Primaries and their Memories

Regular Seminar Sabrina Pasterski (Princeton)

 at: 14:00 QMWroom Zoom abstract: (for Zoom link please email Silvia Nagy s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13.30) ABSTRACT: A universal relationship between asymptotic symmetries, QFT soft theorems, and low energy observables has reinvigorated attempts at flat space holography. We will begin by introducing a map from 4d S-matrix elements to 2d correlators in a putative dual Celestial CFT, and then re-examine the IR triangle from the perspective of our Celestial CFT.

### 05.11.2020 (Thursday)

#### Stringy resurgence: modular graph functions and Poincare series

Regular Seminar Daniele Dorigoni (Durham University)

 at: 15:00 QMWroom Zoom abstract: Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link. Abstract:In string theory SL(2,Z) invariant functions, such as modular graph functions or coefficient functions of higher derivative corrections, are ubiquitous. Using a representation in terms of PoincarÃ© series we can combine different methods for asymptotic expansions and obtain the complete perturbative and non-perturbative expansion. In the case of the higher derivative corrections, these terms have an interpretation in terms of perturbative string loop effects and pairs of instantons/anti-instantons. There will also be a pre-seminar for the students which will begin at 2:30 pm.

### 29.10.2020 (Thursday)

#### From Quantum Field Theory to Quantum Gravity and the Sachdev-Ye-Kitaev model

Regular Seminar Adrian Tanasa (Univ. Bordeaux)

 at: 14:00 QMWroom Zoom - instructions in the abstract abstract: Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link Abstract: In the first part of this talk I will briefly introduce 0-dimensional Quantum Field Theory (QFT) and Matrix Models, which are known to be a succesfull discrete geometrical, QFT approach to 2D Quantum Gravity. I will then move on to Tensor Models, seen as natural QFT generalization of the celebrated Matrix Models. In the next part of the talk I will present the Sachdev-Ye-Kitaev model, which is known to be a toy model for holography, as well as the relations of this SYK model with various Tensor Models. Finally, I will present some recent results on these topics (various diagrammatic results but also the study of the effect of non-Gaussian average over the SYK random couplings).

### 15.10.2020 (Thursday)

#### Covariant phase space with boundaries (please email p.agarwal AT qmul.ac.uk for the zoom link)

Regular Seminar Daniel Harlow (MIT)

 at: 15:00 QMWroom Zoom abstract: The Hamiltonian formulation of mechanics has many advantages, but its standard presentation destroys manifest covariance. This can be avoided by using the "covariant phase formalism" of Iyer and Wald, but until recently this formalism has suffered from several ambiguities related to boundary terms and total derivatives. In this talk I will present a new version of the formalism which incorporates boundary effects from the beginning. This eliminates all ambiguities, and leads to an algorithmic procedure for covariantly constructing the phase space and Hamiltonian of any Lagrangian field theory. It also allows us to confirm that the Poisson bracket in covariant phase space is indeed equivalent to an old proposal of Peierls for computing Poisson brackets covariantly. Along the way I'll illustrate the formalism using various examples. Based on work with Jie-qiang Wu.

### 14.10.2020 (Wednesday)

Polygon Seminar Anatoly Dymarsky (U. Kentucky)

 at: 15:00 QMWroom Zoom abstract: There is a deep relation between classical error-correcting codes, Euclidean lattices, and chiral 2d CFTs. We show this relation extends to include quantum codes, Lorentzian lattices, and non-chiral CFTs. The relation to quantum codes provides a simple way to solve modular bootstrap constraints and identify interesting examples of conformal theories. In particular we construct many examples of physically distinct isospectral theories, examples of "would-be" CFT partition function -- non-holomorphic functions satisfying all constraints of the modular bootstrap, yet not associated with any known CFT, and find theory with the maximal spectral gap among all Narain CFTs with the central charge c=4. At the level of code theories the problem of finding maximal spectral gap reduces to the problem of finding optimal code, leading to "baby bootstrap" program. We also discuss averaging over the ensemble of all CFTs associated with quantum codes, and its possible holographic interpretation. The talk is based on arXiv:2009.01236 and arXiv:2009.01244.

### 01.10.2020 (Thursday)

#### BPS counting with exponential networks (email p.agarwal AT qmul.ac.uk for the zoom link))

Regular Seminar Pietro Longhi (ETH Zurich)

 at: 14:00 QMWroom Zoom abstract: Spectral networks compute certain enumerative invariants associated with Hitchin systems, by focusing on the interplay of certain geometric and combinatorial data within them. In physics, spectral networks count BPS states of class S theories through 2d-4d wall crossing. I will describe a 3d-5d uplift of this based on exponential networks, that computes generalized Donaldson-Thomas invariants of toric Calabi Yau threefolds.

### 24.09.2020 (Thursday)

#### Neural Networks and Quantum Field Theory (please email p.agarwal AT qmul.ac.uk for the zoom link)

Regular Seminar Jim Halverson (Northeastern University in Boston)

 at: 14:00 QMWroom Zoom abstract: We propose a theoretical understanding of neural networks in terms of Wilsonian effective field theory. The correspondence relies on the fact that many asymptotic neural networks are drawn from Gaussian processes, the analog of non-interacting field theories. Moving away from the asymptotic limit yields a non-Gaussian process and corresponds to turning on particle interactions, allowing for the computation of correlation functions of neural network outputs with Feynman diagrams. Minimal non-Gaussian process likelihoods are determined by the most relevant non-Gaussian terms, according to the flow in their coefficients induced by the Wilsonian renormalization group. This yields a direct connection between overparameterization and simplicity of neural network likelihoods. Whether the coefficients are constants or functions may be understood in terms of GP limit symmetries, as expected from 't Hooft's technical naturalness. General theoretical calculations are matched to neural network experiments in the simplest class of models allowing the correspondence. Our formalism is valid for any of the many architectures that becomes a GP in an asymptotic limit, a property preserved under certain types of training.

### 28.05.2020 (Thursday)

#### From Scattering Amplitudes to Results in General Relativity (email p.agarwal AT qmul.ac.uk for the zoom link)

Regular Seminar Emil Bjerrum-Bohr ( Niels Bohr Institute)

 at: 14:00 QMWroom Zoom abstract: Gravity is a fundamental theory of physics, but so weak, that we still know very little about it. A new exciting development is that the Laser Interferometer Gravitational-Wave Observatory (LIGO) can now measure the effects when massive black holes collide in the Universe. This has stimulated many new and interesting studies of gravitational interactions. I will in this talk discuss recent computational advances and discuss how to derive results for observables in general relativity from amplitudes.

### 21.05.2020 (Thursday)

#### Some remarks on the interface of arithmetic geometry and quantum field theory (email p.agarwal AT qmul.ac.uk)

Regular Seminar Minhyong Kim (University of Oxford)

 at: 14:00 QMWroom Zoom abstract: Arithmetic geometry is the study *arithmetic schemes*, mathematical structures that have simultaneously an arithmetic and a geometric structure. The prototype is the so-called *spectrum of the integers* which is a geometric object on which the integers form the ring of functions. I will explain some of the difficult and classical problems that arise in their study, and how ideas of physics, especially topological quantum field theory, may be helpful.

### 14.05.2020 (Thursday)

Regular Seminar Matthias Gaberdiel (ETH Zurich)

 at: 14:00 QMWroom Zoom abstract: String theory on AdS3 x S3 x T4 with one unit of NS-NS flux is argued to be exactly dual to the symmetric orbifold of T4 in the large N limit. The string theory background can be described in terms of a solvable world-sheet theory. This allows one to compute the complete single-string spacetime spectrum and thereby demonstrate that it agrees with the that of the symmetric orbifold of T4. Furthermore, the structure of the symmetric orbifold correlators can be reproduced from the world-sheet perspective.

### 07.05.2020 (Thursday)

#### The Precision Frontier in LHC Simulations (please email p.agarwal AT qmul.ac.uk for a link to the zoom meeting)

Regular Seminar Frank Krauss (Durham University)

 at: 14:00 QMWroom Zoom abstract: In my talk, I will introduce concepts relevant for simulation of LHC physics. I will highlight some of the challenges when going to the level of precision necessary to match experimental accuracy.

### 30.04.2020 (Thursday)

#### Color Confinement and Bose-Einstein condensation (please email p.agarwal AT qmul.ac.uk for a link to the zoom meeting))

Regular Seminar Masanori Hanada (University of Surrey)

 at: 14:00 QMWroom Zoom abstract: We propose a unified description of two important phenomena: color confinement in large-N gauge theory, and Bose-Einstein condensation (BEC). We focus on the confinement/deconfinement transition characterized by the increase of the entropy from N^0 to N^2, which persists in the weak coupling region. Indistinguishability associated with the symmetry group --- SU(N) or O(N) in gauge theory, and S_N permutations in the system of identical bosons --- is crucial for the formation of the condensed (confined) phase. We relate standard criteria, based on off-diagonal long range order (ODLRO) for BEC and the Polyakov loop for gauge theory. The constant offset of the distribution of the phases of the Polyakov loop corresponds to ODLRO, and gives the order parameter for the partially-(de)confined phase at finite coupling. Furthermore we show the numerical evidence for this phenomenon at strong coupling, by using the Yang-Mills matrix model as a concrete example and solving it numerical via lattice simulation. This talk is based on a series of papers, especially "Color Confinement and Bose-Einstein Condensation" by Hanada, Shimada and Wintergerst, 2001.10459 [hep-th] and "Partial Deconfinement at Strong Coupling on a Lattice' by Bergner, Bodendorfer, Funai, Hanada, Rinaldi, Schaefer, Vranas and Watanabe to appear (should be in hep-th by the talk).

### 23.04.2020 (Thursday)

#### De Sitter horizons and holographic bulk reconstruction (please email p.agarwal AT qmul.ac.uk for a link to the zoom meeting))

Regular Seminar Damian Galante (King's College)

 at: 14:00 QMWroom Zoom abstract: Cosmological (or de Sitter) horizons behave qualitatively different to black hole horizons and this poses a challenging problem in the context of holography. In this talk, I will discuss a novel construction to probe de Sitter horizons using the usual tools of the AdS/CFT correspondence. I will further explore ongoing efforts to reconstruct the bulk metric in two dimensions from the dual quantum mechanical correlators in the boundary.

### 16.04.2020 (Thursday)

#### 5d SCFTs and BPS quivers (Please email p.agarwal AT qmul.ac.uk for the zoom link to the meeting)

Regular Seminar Cyril Closset (Oxford)

 at: 14:00 QMWroom Zoom abstract: I will explore aspects of the Coulomb-branch physics of five-dimensional superconformal field theories (SCFT). More precisely, I will consider the 5d SCFT on a circle, and describe the general structure of the Coulomb-branch BPS states as encoded in a "5d BPS quiver," which can be computed from standard string-theory geometric-engineering techniques. The interplay between 4d and 5d BPS quivers will play a central role in our story.

### 23.03.2020 (Monday)

#### TBA

Informal Seminar Severin Bunk (Hamburg University)

 at: 10:30 QMWroom GO Jones 516 abstract:

### 12.03.2020 (Thursday)

#### Cancelled

Regular Seminar Valya Khoze (Durham University)

 at: 14:00 QMWroom GO Jones 610 abstract: