## 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)

### 22.02.2019 (Friday)

#### Hecke relations and Galois symmetries in Rational Conformal Field Theories and Modular Tensor Categories

Exceptional Seminar Jeff Harvey (The University of Chicago)

 at: 11:30 QMWroom 610 abstract: I will discuss some old and new relations between the characters, modular data and braiding and fusing matrices of rational conformal field theories and their associated modular tensor categories. These relations involve concepts from number theory which I will explain in the talk.

### 21.02.2019 (Thursday)

#### tba

Regular Seminar Marco Meineri (EPFL, Lausanne)

 at: 14:00 QMWroom G O Jones 610 abstract: tba

### 14.02.2019 (Thursday)

#### How logarithms are born

Regular Seminar Melissa van Beekveld (IMAPP Njimegen)

 at: 14:00 QMWroom G O Jones 610 abstract: I will show how large logarithms arise in a perturbative calculation and how resummation solves the issue of having these large logarithms. If there is some time left, I want to show some recent progress that we have made on pinning down the origin of the next-to-leading class of logarithms.

### 31.01.2019 (Thursday)

#### Field theory of gapped momentum states

Regular Seminar Kostya Trachenko (QMUL)

 at: 14:00 QMWroom G O Jones 610 abstract: Understanding most basic thermodynamic properties of liquids such as energy and heat capacity turned out to be a long-standing problem in physics [1]. Landau&Lifshitz textbook states that no general formulas can be derived for liquid thermodynamic functions because the interactions are both strong and system-specific. Phrased differently, liquids have no small parameter. Recent results have opened a new way to understand liquid thermodynamics on the basis of collective modes (phonons) as is done in the solid state theory. There are important differences between phonons in solids and liquids, and we have recently started to understand and quantify this difference. One striking difference is the emergence of a gap in the liquid phonon spectrum in the reciprocal space [2]. This brings an interesting question of what kind of field theory describes this gap. We recently proposed a two-field Lagrangian which accounts for dissipation and predicts the gap in momentum space [3]. The dissipative and mass terms compete by promoting gaps in k-space and energy, respectively (when bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.) I will also discuss the recent attempt to canonically quantize this theory where I attempted to describe quantum dissipation which has been of interest recently. The Hamiltonian is quantized in terms of particles and antiparticles as in the complex scalar field theory and has the energy spectrum with the gap in momentum space. Finally, I will discuss the emergence of ultraviolet and infrared cutoffs in this theory due to dissipation. [1] K. Trachenko and V. V. Brazhkin, Collective modes and thermodynamics of the liquid state, Reports on Progress in Physics 79, 016502 (2016). [2] C. Yang, M. T. Dove, V. V. Brazhkin and K. Trachenko, Physical Review Letters 118, 215502 (2017). [3] K. Trachenko, Physical Review E 96, 062134 (2017).

### 24.01.2019 (Thursday)

#### The Uses of Lattice Topological Defects

Regular Seminar Paul Fendley (Oxford)

 at: 14:00 QMWroom G O Jones 610 abstract: I give an overview of work with Aasen and Mong on topological defects in two-dimensional classical lattice models, quantum spin chains and tensor networks. The partition function in the presence of a topological defect is invariant under any local deformation of the defect. By using results from fusion categories, we construct topological defects in a wide class of lattice models, and show how to use them to derive exact properties of field theories by explicit lattice calculations. In the Ising model, the fusion of duality defects allows Kramers-Wannier duality to be enacted on the torus and higher genus surfaces easily, implementing modular invariance directly on the lattice. In other models, the construction leads to generalised dualities previously unknown. A consequence is an explicit definition of twisted boundary conditions that yield the precise shift in momentum quantization and for critical theories, the spin of the associated conformal field. Other universal quantities we compute exactly on the lattice are the ratios of g-factors for conformal boundary conditions

### 17.01.2019 (Thursday)

#### 4D scattering equations, Monte Carlo methods, and conformal supergravity

Regular Seminar Joseph Farrow (Durham U.)

 at: 14:00 QMWroom G O Jones 610 abstract: I will introduce the framework of 4D scattering equations for calculating tree level super amplitudes in a variety of different theories, including Einstein supergravity and super Yang-Mills theory. I will discuss my work on numerical solutions to these equations by Monte Carlo methods, and work with Arthur Lipstein on calculating N=4 conformal supergravity amplitudes in this framework.

### 13.12.2018 (Thursday)

#### Genus-One String Amplitudes from Conformal Field Theory

Regular Seminar Luis Fernando Alday (Oxford)

 at: 14:00 QMWroom G O Jones 610 abstract:

### 05.12.2018 (Wednesday)

#### Graphene and Boundary Conformal Field Theory

Triangular Seminar Christopher Herzog (KCL)

 at: 15:00 QMWroom Fogg Lecture Theatre abstract: The infrared fixed point of graphene under the renormalization group flow is a relatively under studied yet important example of a boundary conformal field theory with a number of remarkable properties. It has a close relationship with three dimensional QED. It maps to itself under electric-magnetic duality. Moreover, it along with its supersymmetric cousins all possess an exactly marginal coupling -- the charge of the electron -- which allows for straightforward perturbative calculations in the weak coupling limit. I will review past work on this model and also discuss my own contributions, which focus on understanding the boundary contributions to the anomalous trace of the stress tensor and their role in helping to understand the structure of boundary conformal field theory.

### 05.12.2018 (Wednesday)

#### How to Build the Thermofield Double State

Triangular Seminar Diego Hofman (Amsterdam)

 at: 16:30 QMWroom Fogg Lecture Theatre abstract: Given two copies of any quantum mechanical system, one may want to prepare them in the thermofield double state for the purpose of studying thermal physics or black holes. However, the thermofield double is a unique entangled pure state and may be difficult to prepare. We propose a local interacting Hamiltonian for the combined system whose ground state is approximately the thermofield double. The energy gap for this Hamiltonian is of order the temperature. Our construction works for any quantum system satisfying the Eigenvalue Thermalization Hypothesis.

### 29.11.2018 (Thursday)

#### Walking, weakly first order phase transitions and complex CFTs

Regular Seminar Bernardo Zan (EPFL Lausanne)

 at: 14:00 QMWroom G O Jones 610 abstract: I will discuss walking behavior in gauge theories and weakly first order phase transition in statistical models. Despite being phenomena appearing in very different physical systems, they both show a region of approximate scale invariance. They can be understood as a RG flow passing between two fixed points living at complex couplings, which we call complex CFTs. By using conformal perturbation theory, knowing the conformal data of the complex CFTs allows us to make predictions on the observables of the walking theory. As an example, I will discuss the two dimensional Q-state Potts model with Q>4.

### 22.11.2018 (Thursday)

#### Holographic relative entropy in infinite-dimensional Hilbert spaces

Regular Seminar Monica Kang (Harvard)

 at: 14:00 QMWroom G O Jones 610 abstract: Quantum error correction provides a convenient setup where bulk operators are defined only on a code subspace of the physical Hilbert space of the conformal field theory. I will first reformulate entanglement wedge reconstruction in the language of operator-algebra quantum error correction with infinite-dimensional physical and code Hilbert spaces. I will streamline my proof that for infinite-dimensional Hilbert spaces, the entanglement wedge reconstruction is identical to the equivalence of the boundary and bulk relative entropies. I will discuss its implications for holographic theories with the Reeh-Schlieder theorem.

### 15.11.2018 (Thursday)

#### Free Field Realizations from the Higgs Branch

Regular Seminar Carlo Meneghelli (Oxford)

 at: 14:00 QMWroom G O Jones 610 abstract: To any four-dimensional N=2 super-conformal field theory (SCFT) one can canonically associate a two-dimensional vertex operator algebra (VOA). This provides a powerful framework for the analysis of SCFTs and leads to surprising predictions for a large new class of VOAs. In this talk I will present remarkable free field realizations of the relevant VOAs which mirror the effective field theory description of the corresponding four dimensional theory on the Higgs branch of its moduli space of vacua.

### 01.11.2018 (Thursday)

#### Twisted BRST quantization and localization in supergravity

Regular Seminar Sameer Murthy (KCL)

 at: 14:00 QMWroom G O Jones 610 abstract: Supersymmetric localization is a powerful technique to evaluate a class of functional integrals in supersymmetric field theories. It reduces the functional integral over field space to ordinary integrals over the space of solutions of the off-shell BPS equations. The application of this technique to supergravity suffers from some problems, both conceptual and practical. I will discuss one of the main conceptual problems, namely how to construct the fermionic symmetry with which to localize. I will show how a deformation of the BRST technique allows us to do this. As an application I will then sketch a computation of the one-loop determinant of the super-graviton that enters the localization formula for BPS black hole entropy.

### 25.10.2018 (Thursday)

#### Lessons from CFTs on nontrivial manifolds

Regular Seminar Anastasios Petkou (Aristotle University of Thessaloniki)

 at: 14:00 QMWroom G O Jones 610 abstract: Even if one knows everything for a conformal field theory on the infinite plane, new data are required to place the same theory in finite geometries. This is a physically relevant question for finite-temperature/finite-size critical systems. I will show in this talk how to apply an OPE inversion formula to thermal two-point functions of bosonic and fermionic CFTs in general odd dimensions. This allows us to analyze in detail the operator spectrum of these theories. The main result is that nontrivial thermal CFTs arise when the thermal mass satisfies an algebraic transcendental equation that ensures the absence of an infinite set of operators from the spectrum. The solutions of these gap equations for general odd dimensions are in general complex numbers and follow a particular pattern. I will argue that this pattern unveils the large-N vacuum structure of the corresponding theories at zero temperature.

### 17.10.2018 (Wednesday)

#### Non-planar Scattering Amplitude - Wilson Loop Duality

Regular Seminar Alexander Tumanov (Tel Aviv U.)

 at: 11:30 QMWroom G O Jones 610 abstract: Higher order corrections in the 1/N expansion to scattering amplitudes come from the diagrams with higher genus. One way to address these non-trivial topologies is to view them as planar objects glued into non-planar configurations. They can then be "cut" across all the cycles of the corresponding Riemann surface, fixing the momentum flowing in each cycle. This procedure results in a planar object that belongs to a representation of the modular group of the Riemann surface in question. Various techniques developed for the planar amplitudes can be generalized to these cut non-planar ones. We will investigate the scattering amplitude — Wilson loop duality, specifically focusing on the case of the first non-planar correction, 1/N double trace amplitude, which has the topology of a cylinder. It’s dual space interpretation is a correlator of two infinite Wilson lines subject to a periodicity constraint. We will confirm this duality by a weak coupling perturbative calculation and a strong coupling string worldsheet one. This will allow us to construct the non-planar loop integrands and the BCFW recursion relation they satisfy, as well as to find an interpretation of the dual conformal symmetry in the non-planar sector, which was previously thought to be broken by 1/N corrections. Lastly, we will discuss this result in the framework of the Wilson Loop OPE approach, which allows one to compute expectation values of Wilson loops at any value of the coupling in the form of an expansion around the collinear limit. We claim that this approach can be directly applied to cut non-planar scattering amplitudes, as well as the N=4 SYM form factors, whose dual space interpretation is remarkably similar to the one of the 1/N amplitude correction.

### 17.10.2018 (Wednesday)

#### Aspects of de Sitter spacetimes

Triangular Seminar Dionysios Anninos (Amsterdam)

 at: 15:00 QMWroom Fogg Lecture Theatre abstract: We overview some aspects of asymptotically de Sitter spacetimes at the classical and quantum level. We discuss some features of the late time de Sitter wavefunction. We briefly touch upon some properties of the relation between de Sitter space and Euclidean conformal theories, broadly referred to as the dS/CFT correspondence. Finally, time permitting, we will discuss some similarities and differences between the cosmological dS horizon and a more standard black hole horizon.

### 11.10.2018 (Thursday)

#### Some lessons from/for Supergravity in AdS4/CFT3

Regular Seminar Costantin Bachas (ENS Paris)

 at: 14:00 QMWroom G O Jones 610 abstract: I will first review the AdS4/SCFT3 correspondence with N=4 supersymmetry. I will then focus on two special aspects which are important in exploring the string landscape: (1) The existence of N=2 moduli and their fate in gauged supergravity; (2) Special degeneration limits for which the low-energy limit is a theory of bigravity or massive gravity.

### 04.10.2018 (Thursday)

#### Disconnected gauge theories

Regular Seminar Diego Rodriguez-Gomez (Oviedo U.)

 at: 14:00 QMWroom G O Jones 610 abstract: Disconnected gauge groups have been, at least comparatively, very poorly studied. Yet they may hide very interesting Physics. Recently, a class of gauge theories based on a particular type of disconnected gauge groups, namely principal extensions, has been introduced. Interestingly, such theories naturally implement the gauging of charge conjugation. In this talk, we will describe such construction and study aspects of its Physics. A particularly spectacular by-product of the construction is that these theories have non-freely generated Coulomb branches, thus providing the first counterexample of the long standing standard lore that Coulomb branch are all freely generated.

### 27.09.2018 (Thursday)

#### Amplitudes and hidden symmetries in supersymmetric Chern-Simons matter theories

Regular Seminar Karthik Inbasekar (Tel Aviv U.)

 at: 14:00 QMWroom G O Jones 610 abstract: Chern-Simons theories coupled to fundamental matter have a wide variety of applications ranging from Quantum Hall effect to Quantum gravity via AdS/CFT. These theories enjoy a strong weak duality that has been tested to a very good accuracy via large N computations, such as thermal partition functions, and S matrices. Supersymmetric Chern-Simons theories are equally interesting since they have a self duality and relate to non-supersymmetric theories via RG flows. In the N=2,3 supersymmetric Chern-Simons matter theories, the four point amplitude computed to all orders in the 't Hooft coupling is not renormalised! It is a unique situation in a quantum field theory that the scattering amplitude doesn't receive loop corrections. This indicates the presence of powerful symmetry structures within the theory. This also suggests that higher point amplitudes may be easier to compute using four point amplitudes as building blocks. These higher point amplitudes not only serve as a testing tool for duality but also a probe into the symmetry structure of the theory. As a first step towards this goal, we begin by computing arbitrary n point tree level amplitudes in the N=2 theory via BCFW recursion relations. We then show that the four point tree level amplitude enjoys a dual superconformal symmetry. Since the all loop four point amplitude is tree level exact, it follows that the dual superconformal symmetry is exact to all loops. This is in contrast to highly supersymmetric examples such as N=4 SYM and N=6 ABJM, where the dual superconformal symmetry is in general anomalous. Furthermore, we show that the superconformal and dual superconformal symmetries generate an infinite dimensional Yangian symmetry for the four point amplitude. If these symmetries persist to higher point amplitudes, this suggests that the N=2 superconformal Chern-Simons matter theory may be integrable.

### 20.09.2018 (Thursday)

#### Entanglement branes in a two-dimensional string theory

Regular Seminar Gabriel Wong (Fudan U)

 at: 14:00 QMWroom G O Jones 610 abstract: What is the meaning of entanglement in a theory of extended objects such as strings? To address this question we consider the spatial entanglement between two intervals in the Gross-Taylor model, the string theory dual to two-dimensional Yang-Mills theory at large N. The string diagrams that contribute to the entanglement entropy describe open strings with endpoints anchored to the entangling surface, as first argued by Susskind. We develop a canonical theory of these open strings, and describe how closed strings are divided into open strings at the level of the Hilbert space. We derive the Modular hamiltonian for the Hartle-Hawking state and show that the corresponding reduced density matrix describes a thermal ensemble of open strings ending on an object at the entangling surface that we call an E-brane.