This week

Monday

Lonti: Conformal blocks in two dimensions

Regular Seminar Gerard Watts (KCL)

at:
10:30 KCL
room Online
abstract:

This is the live session included as part of the LonTI lecture on Conformal blocks in two dimensions. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.​​Conformal blocks are the building blocks of conformal field theories, the key ingredients of correlation functions and knowledge of these blocks is central to the conformal bootstrap. This lecture covers some general results before quickly specialising to two-dimensions. It discusses the implications of global conformal invariance and then the larger and more constraining Virasoro algebra symmetry. It introduces various methods of calculation including brute force, differential equations, recursion relations and closed formulae - and some aspects of bootstrap techniques.

LonTI 2020: D-branes and boundary states

Regular Seminar Bogdan Stefanski (City)

at:
14:00 City U.
room Youtube
abstract:

D-branes are a remarkable set of soliton-like objects in string theory which have played a critical role in many areas of string theory. Despite being non-perturbative, they can be understood exactly using world-sheet methods through the boundary state formalism. In this lecture, I introduce the notion of a boundary state and show how to use it to extract physical information about D-branes and the open strings that live on them.

Tuesday

Smashing Solitons of Cosmology

Regular Seminar Mustafa Amin (Rice University, Houston, Texas)

at:
13:30 IC
room zoom 871 9223 5980
abstract:

Long-lived, spatially-localized and coherently oscillating field configurations (pseudo-solitons, for example, axion stars and oscillons) can form naturally in cosmologically relevant axion-like fields constituting dark matter today or in fields at the end of inflation. When these clumps collide and merge, they can give rise to bursts of electromagnetic and gravitational waves. In this talk, I will first discuss earlier work on soliton formation mechanisms and their interactions, as well as gravitational wave production. Then, for the main part of the talk, I will focus on the production of potentially detectable electromagnetic bursts resulting from the merger of dense scalar field oscillons/axion stars in the current universe [this is based on our recent paper, https://arxiv.org/abs/2009.11337]. Time permitting, I will also discuss possible connections to Fast Radio Bursts. [please email a.held@imperial.ac.uk for zoom link or password]

Wednesday

A novel twistor string theory

Triangular Seminar Kevin Costello (Perimeter Institute)

at:
15:00 City U.
room Zoom
abstract:

This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link. I will report on some work in progress on type I topological strings on twistor space, and their relationship with integrable but non-supersymmetric field theories in three and four dimensions. This is closely related to recent work of Bittleston and Skinner.

Numerical CY metrics from holomorphic networks

Triangular Seminar Michael Douglas (Simons Center for Geometry and Physics)

at:
16:30 City U.
room Zoom
abstract:

This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link. We propose machine learning inspired methods for computing numerical Calabi-Yau metrics, and implement them using Tensorflow/Keras. We compare them with previous work, and find that they are far more accurate for manifolds with little or no symmetry. We also discuss issues such as optimization methods, overparameterization and computational complexity. Joint work with Subramanian Lakshminarasimhan and Yidi Qi.

Thursday

Phases of unitary matrix models and lattice QCD in two dimensions

Journal Club Jorge Russo (University of Barcelona)

at:
15:15 Other
room Zoom, instructions in abstract
abstract:

We investigate the different large N phases of a deformed Gross-Witten-Wadia U(N) matrix model. The deformation, which leads to a solvable model, corresponds to the addition of characteristic polynomial insertions and mimicks the one-loop determinant of fermion matter. In one version of the model, the GWW phase transition is smoothed out and it becomes a crossover. In another version, the phase transition occurs along a critical line in the two-dimensional parameter space spanned by the 't~Hooft coupling $\lambda $ and the Veneziano parameter $\tau $. A calculation of the $\beta $ function shows the existence of an IR stable fixed point. ---- Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.

Topologically Ordered Matter and Why You Should be Interested

Regular Seminar Steven Simon (Oxford)

at:
14:00 QMW
room 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.

TBA

Regular Seminar Costas Bachas (Ecole Normale Superieure)

at:
14:00 IC
room Zoom
abstract: