Recent seminars

Europe/Lisbon
Online

Ingo Runkel
Ingo Runkel, University of Hamburg

Topological symmetries and their gaugings in 2d CFT and 3d TFT

The study of topological defects in quantum field theory has seen a wealth of activity recently leading to many interesting insights, for example the explicit realisation of non-invertible topological defects in higher dimensional QFTs via the gauging of higher form symmetries, or the description of the higher algebraic structures inherent in these topological defects. In this talk, I would like to focus on low-dimensional examples, where such defects and their properties have been investigated for some time already. I would like to exhibit some of the properties of topological defects in two-dimensional conformal field theory and in three-dimensional topological field theory, and show some of the structural insights into 2d CFT and 3d TFT one can gain with the help of defects. In this way, the well-understood low-dimensional case might serve as a source of ideas and as a test case for higher dimensional constructions.

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Ingo's slides.

Europe/Lisbon
Online

Clément Delcamp
Clément Delcamp, Institut des Hautes Études Scientifiques

Topological symmetry and duality in quantum lattice models

Defining internal symmetry in a quantum theory through the lens of topological defects opens the door to generalised notions of symmetry, including some arising from non-invertible transformations, and enables a calculus that leverages well-established methods from topological quantum field theory. In d spatial dimensions, the framework of fusion d-category theory is believed to offer an axiomatisation for finite non-invertible symmetries. Though seemingly exotic, such non-invertible symmetries can be shown to naturally arise as dual symmetries upon gauging invertible symmetries. In this talk, I will present a framework to systematically investigate these aspects in quantum lattice models.

Europe/Lisbon
Online

Matthias Ludewig
Matthias Ludewig, University of Greifswald

The stringor bundle and the spinor bundle on loop space

We explain the construction of the stringor bundle on a string manifold recently given in joint work with Peter Kristel and Konrad Waldorf. We start by discussing the spinor bundle on the loop space of a string manifold, together with its fusion product. Then we explain how the stringor bundle on the manifold itself can be obtained using a regression procedure.

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Matthias's slides.