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)

10.11.2016 (Thursday)

Twistors and Conformal Higher-Spin Theory

Regular Seminar Tristan McLoughlin (Trinity College Dublin)

at:
14:00 QMW
room G.O. Jones 610
abstract:

Higher-spin fields can play an important role in effective field theories and increasingly are of interest due to their appearance in recent studies of holography. Understanding their interactions is however often involved and searching for alternative formulations could be very useful. In this talk we will consider one such formulation, namely twistors. After giving a general introduction to the use of twistors in describing the dynamics of massless field theories, we will focus on the construction of off-shell actions directly in twistor space including a recent higher-spin generalisation of self-dual Weyl gravity. We will show how this formulation produces the expected flat space-time spectrum and linearised symmetries. In analogy with the known embedding of Einstein gravity inside Weyl gravity, we identify a ghost free sub-sector of the conformal higher-spin theory and consider its cubic couplings. Finally we describe proposed anti-self-dual interaction terms to extend the twistor action to the full conformal higher-spin theory.

03.11.2016 (Thursday)

Strings and High Energy Scattering

Regular Seminar Volker Schomerus (Desy Hamburg)

at:
14:00 QMW
room G.O. Jones 610
abstract:

The high energy behavior of physical scattering amplitudes challenged early string theory. With the discovery of gauge-string dualities the obstacle was overcome and today string theory provides precision results, in particular for the high energy limit. In my talk I will review the many facets of integrability in high energy scattering at weak, intermediate and strong coupling.

27.10.2016 (Thursday)

A c-Theorem for Two-dimensional Boundaries and Defects

Regular Seminar Andy O'Bannon (Southampton)

at:
14:00 QMW
room G.O. Jones 610
abstract:

I will present a proof for a monotonicity theorem, or c-theorem, for a three-dimensional Conformal Field Theory (CFT) on a space with a boundary, and for a higher-dimensional CFT with a two-dimensional defect. The proof is applicable only to renormalization group flows that preserve locality, reflection positivity, and Euclidean invariance along the boundary or defect, and that are localized at the boundary or defect, such that the bulk theory remains conformal along the flow. The method of proof is a generalization of Komargodski’s proof of Zamolodchikov’s c-theorem. The key ingredient is an external “dilaton” field introduced to match Weyl anomalies between the ultra-violet (UV) and infra-red (IR) fixed points. Reflection positivity in the dilaton’s effective action guarantees that a certain coefficient in the boundary/defect Weyl anomaly must take a value in the UV that is larger than (or equal to) the value in the IR. This boundary/defect c-theorem may have important implications for many theoretical and experimental systems, ranging from graphene to branes in string theory and M-theory.

19.10.2016 (Wednesday)

Polygon Seminar: Algebraic methods for classical integrability

Triangular Seminar Alessandro Torrielli (Surrey)

at:
15:00 QMW
room G.O. Jones 610
abstract:

We will review a series of algebraic techniques to describe classically integrable systems, with an eye to their quantisation. The topics we shall attempt to cover will be: 1. General introduction to classical integrability and notion of Lax pair 2. Classical r-matrices and exchange relations 3. Belavin-Drinfeld theorems and classifications 4. Quantisation and elements of algebraic Bethe ansatz

13.10.2016 (Thursday)

N=2 super Yang-Mills and the Geometry of Magnetic Monopoles

Regular Seminar Andy Royston (Texas U.)

at:
14:00 QMW
room G.O. Jones 610
abstract:

In this talk we consider BPS states in 4D, N=2 gauge theory in the presence of defects. We give a semiclassical description of these `framed BPS states' in terms of kernels of Dirac operators on moduli spaces of singular monopoles. For both framed and ordinary BPS states we present a conjectural map between the data of the semiclassical construction and the data of the low-energy, quantum-exact Seiberg-Witten description. This map incorporates both perturbative and nonperturbative field theory corrections to the supersymmetric quantum mechanics of the monopole collective coordinates. We use it to translate recent developments in the study of N=2 theories, including wall-crossing formulae and the no-exotics theorem, into geometric statements about the Dirac kernels. The no-exotics theorem implies a broad generalization of Sen's conjecture concerning the existence of L^2 harmonic forms on monopole moduli space. This talk is based on work done in collaboration with Greg Moore and Dieter Van den Bleeken.

12.10.2016 (Wednesday)

Covariant quantum spaces and emergent gravity in the IKKT matrix model

Regular Seminar Harold Steinacker (Vienna U.)

at:
16:00 QMW
room G.O. Jones 610
abstract:

We study perturbations of 4-dimensional fuzzy spheres as backgrounds in the IKKT or IIB matrix model. Gauge fields and metric fluctuations are identified among the excitation modes with lowest spin, supplemented by a tower of higher-spin fields. They arise from an internal structure which can be viewed as a twisted bundle over S^4, leading to a covariant noncommutative geometry. The linearized 4-dimensional Einstein equations are obtained from the classical matrix model action under certain conditions, modified by an IR cutoff. Some one-loop contributions to the effective action are computed using the formalism of string states.

06.10.2016 (Thursday)

Geometry = Efficiency? Decoding the DNA of Prediction

Regular Seminar John Joseph Carrasco (CEA)

at:
14:00 QMW
room G.O. Jones 610
abstract:

One can easily be frustrated by the tremendous redundancy in possible physical description. By this I mean the freedom to choose gauge, make field redefinitions, add any amount of auxiliary spectator matter, and the such. Happily we can exploit such freedom to encourage the emergence of a new duality in gauge theories. The existence of a duality between color and kinematics exposes a hidden local double-copy structure inherent to prediction in many theories. This structure weaves its way between theories both formal and phenomenological, from QCD to Gravity, from Chiral Perturbation Theory to Born-Infeld and Volkov-Akulov, and from open to closed superstring theories. The duality is sharpest at the level of the perturbative S-matrix — so I will focus my talk there, although I will also mention some recent provocative work beyond scattering. I will mainly discuss progress and challenges to generically achieving color-dual kinematic representations at the multi-loop level. I present a path forward that introduces, at least temporarily, a redundancy of description that we can exploit to map a set of functional relations to linear ones. I will talk about this approach in terms of a geometric picture involving the graph of local graphs, discussing tradeoffs and applicability to long-standing problems.

29.09.2016 (Thursday)

On the null origin of the ambitwistor string

Regular Seminar Eduardo Casali (Oxford U.)

at:
14:00 QMW
room G.O. Jones 610
abstract:

The Cachazo-He-Yuan (CHY) formulas are a remarkable representation of tree-level massless scattering amplitudes. Similarly to the Twistor String formulas, the CHY formula presents amplitudes as an integrals over the moduli space of Riemann surfaces constrained to the solutions of a set of algebraic equations called the scattering equations. But contrary to the Twistor String formulas, they can be written in for any dimension and for a variety of massless theories. Behind the original CHY formula and the scattering equations lies a 2D CFT called the Ambitwistor String, much like the original Twistor String, this is a chiral CFT in which correlators of vertex operators reproduce the CHY formulas and give a geometric interpretation of the scattering equations. The Ambitwistor string possesses a few peculiar characteristics when viewed as a string theory, its low energy efective action is the same as Type II closed strings but the appearance of the scattering equations suggests a high-energy limit has been taken a la Gross and Mende. Besides, its genus one correlation functions are modular invariant but UV divergent since they correspond to 10D SUGRA amplitudes. In this talk I'll talk about a program started with P. Tourkine in which the Ambitwistor String (and other Twistor Strings) are treated as coming from the tensionless limit of classcial string theories. These are know as null strings and have a long history in the literature. I'll review the null string and its supersymmetric extensions and show how the Ambitwistor String can be obtained from a particular gauge fixing of the null string. In doing so, I'll address the issue of possible inequivalent quantizations of the null string and compare it to the case of the usual string and shed a light its relation to the Ambitwistor String.

15.09.2016 (Thursday)

Holography inspired stringy hadrons

Regular Seminar Cobi Sonnenschein (Tel Aviv University)

at:
14:00 QMW
room G.O. Jones 610
abstract:

23.06.2016 (Thursday)

Bremsstrahlung function, leading Luscher correction at weak coupling and localization

Regular Seminar Michelangelo Preti (Parma U.)

at:
14:00 QMW
room G.O. Jones 610
abstract:

We discuss the near BPS expansion of the generalized cusp anomalous dimension with L units of R-charge. Integrability provides an exact solution, obtained by solving a general TBA equation in the appropriate limit: we propose here an alternative method based on supersymmetric localization. The basic idea is to relate the computation to the vacuum expectation value of certain 1/8 BPS Wilson loops with local operator insertions along the contour. These observables localize on a two-dimensional gauge theory on S^2, opening the possibility of exact calculations. As a test of our proposal, we reproduce the leading Luscher correction at weak coupling to the generalized cusp anomalous dimension. This result is also checked against a genuine Feynman diagram approach in N=4 Super Yang-Mills theory.

16.06.2016 (Thursday)

Surface defects as vortex strings in class S_k

Regular Seminar Hironori Mori (Osaka University)

at:
14:00 QMW
room G.O. Jones 610
abstract:

We investigate the aspects of surface defects in a new class of 4d N=1 superconformal quiver theories named class S_k. As the first step, we focus on the construction of the surface defects in IR under the situation where the UV theories of class S_k are higgsed by giving the vevs to some fields and try to specify them as 2d N=(0,2) vortex string theories by computing its elliptic genera encoded in the IR description of the superconformal indices of class S_k. This picture is consistent with type IIA brane construction of the vortex strings. Another way to argue the surface defects is to see their actions on the superconformal indices as difference operators, and we would like to discuss whether such difference operators form the algebras labelled by the representations of SU(N) flavor symmetries.

02.06.2016 (Thursday)

Supertanslation symmetry at the black hole horizon

Regular Seminar Gaston Giribet (University of Buenos Aires)

at:
14:00 QMW
room G.O. Jones 610
abstract:

26.05.2016 (Thursday)

Super String Field Theory Revisited

Regular Seminar Ivo Sachs (LMU)

at:
14:00 QMW
room G.O. Jones 610
abstract:

I first describe the remarkably simple algebraic structure underlying covariant string field theory. No knowledge of string field theory and only very basic concepts of string theory are required for this. I then use this structure to construct the superstring field theory action recursively and discuss its relation to the decomposition of (super) moduli spaces. I will focus mostly on open string theory but will comment on the generalisation to closed string.

20.05.2016 (Friday)

Graduate Mini-Course: Sectors of Supersymmetric Field Theories

Informal Seminar Matthew Buican (QMUL)

at:
10:30 QMW
room GOJ 610
abstract:

Lecture 3: "Toward a Synthesis of Chiral Rings and Chiral Algebras." I will aim to discuss some recent work that seeks to relate the objects introduced in the first two lectures. Given enough time, we may also discuss generalizations of these ideas.

19.05.2016 (Thursday)

d-Dimensional Generalised Unitarity and Colour-Kinematics duality

Regular Seminar William Javier Torres Bobadilla (Padua U.)

at:
14:00 QMW
room G.O. Jones 610
abstract:

In this talk I plan to introduce the Four-Dimensional-Formulation (FDF) regularisation scheme proposed in arXiv:1404.4783 [hep-ph], which allows a four-dimensional representation of the d-dimensional particles propagating in the loop. Within FDF, I present the computation of one-loop QCD corrections of the processes gg>>gggg and gg>>Hggg (in the heavy top limit). On the other hand, I show the extension of Colour-Kinematics relations in d-dimensions and their application to compute efficiently one-loop amplitudes.

18.05.2016 (Wednesday)

Graduate Mini-Course: Sectors of Supersymmetric Field Theories

Informal Seminar Matthew Buican (QMUL)

at:
10:30 QMW
room GOJ 610
abstract:

Lecture 2: "Chiral Algebras and Higher-Dimensional Theories." I will review briefly review the construction of chiral algebras and then focus on their relationship with a particular sub-sector of operators in higher-dimensional theories. I will again focus mostly on 4D N=2 theories.

16.05.2016 (Monday)

Graduate Mini-Course: Sectors of Supersymmetric Field Theories

Informal Seminar Matthew Buican (QMUL)

at:
10:30 QMW
room GOJ 610
abstract:

Lecture 1: "Chiral Rings, Moduli Spaces, and Conformal Manifolds." In this lecture I will review basic aspects of chiral operators, with a special focus on 4D theories with 8 Poincare supercharges (i.e., N=2 SUSY). Using these operators, I will discuss basic aspects of moduli spaces and conformal manifolds.

12.05.2016 (Thursday)

One-point Functions of AdS/dCFT from Matrix Product States

Regular Seminar Charlotte Kristjansen (NBI)

at:
14:00 QMW
room G.O. Jones 610
abstract:

One-point functions of certain non-protected scalar operators in the defect CFT dual to the D3-D5 probe brane system with k units of world volume flux can be expressed as overlaps between Bethe eigenstates of the Heisenberg spin chain and a matrix product state. We present a closed expression of determinant form for these one-point functions, valid for any value of k. The determinant formula factorizes into the k=2 result times a k-dependent prefactor. Making use of the transfer matrix of the Heisenberg spin chain we recursively relate the matrix product state for higher even and odd k to the matrix product state for k=2 and k=3 respectively. We furthermore find evidence that the matrix product states for k=2 and k=3 are related via a ratio of Baxter's Q-operators. The general k formula has an interesting thermodynamical limit involving a non-trivial scaling of k, which indicates that the match between string and field theory one-point functions found for chiral primaries might be tested for non-protected operators as well. We revisit the string computation for chiral primaries and discuss how it can be extended to non-protected operators.

05.05.2016 (Thursday)

Quantum Linguistics?

Regular Seminar Mehrnoosh Sadrzadeh (QMUL)

at:
14:00 QMW
room G.O. Jones 610
abstract:

Mathematical models of natural language can be organised into logical and statistical. The former are based on grammatical structures of phrases and sentences and the latter on distributions of words in corpora of text. In joint work with Clark (Cambridge) and Coecke (Oxford), we developed a unifying framework where the distributions of words are composed to form distributions for phrases and sentences. This expanded the application domains of the statistical models -- e.g. automatic reasoning about similarity -- from words to phrases and sentences. On the theoretical side, our model extends the word-based setting from vectors to tensors. Tensors are main players in the mathematical models of quantum mechanics. In this talk, I will review the theory and applications of our model in simple terms and through examples. I will briefly explain how `entanglement', a concept arising from tensors in quantum mechanics, manifests itself and is used as a resource in the linguistic applications. I will also explain how the reasoning toolkit used in this model is the same as that of Abramsky and Coecke in their categorical Quantum Mechanics model.

28.04.2016 (Thursday)

Black Hole Collisions in Asymptotically anti-de Sitter Spacetimes

Regular Seminar Hans Bantilan (QMUL)

at:
14:00 QMW
room G.O. Jones 610
abstract:

The collision of black holes is a classic problem in the strong-field regime of general relativity, with no known closed-form solution. When exact solutions are not known, or perturbative expansions about known solutions are inadequate to capture the non-linear dynamics, the numerical solution of the Einstein field equations is required. The main purpose of this talk is to describe, in detail, the necessary ingredients for achieving stable Cauchy evolution of black hole collisions in asymptotically anti-de Sitter (AdS) spacetimes. I will begin by motivating this program in terms of the heavy-ion physics it is intended to clarify. I will then give an overview of anti-de Sitter space, the mapping to its dual boundary conformal field theory, and the method we use to numerically solve the fully non-linear Einstein field equations with AdS boundary conditions. As a concrete example of these ideas, I will describe simulations of stable AdS black hole mergers in 5 dimensions.