Unless otherwise stated, seminars
will take place in Lecture Theatre 2 of the
Appleton Tower
at
the University of Edinburgh.

Please contact the organisers Andrea Cristofoli (UoE) or Bernard Rybolowicz (HW)
with any questions regarding the seminars.

We are piloting a hybrid seminar format. Speakers
and attendees can opt to join in-person or remotely
using Zoom. Instructions for Zoom attendees will be
shared before each seminar.

Wednesday,
14 December 2022

ICMS Lecture Theatre

13:30

A pre-seminar is a session during which speakers will give a short introduction to their talks.

14:30

Arpit Das
(Durham University)

In this talk, we will discuss QED at finite temperature from a hydrodynamic viewpoint. In the first part of the talk we shall discuss the symmetries of QED using the notion of higher-form symmetries. In the second part of the talk, we will discuss a holographic model which has the same higher-form symmetry structure. We will also very briefly touch upon work in progress regarding an effective hydrodynamic description of QED at T>0, using non-invertible symmetries.

16:00

Peter Schupp
(Jacobs University Bremen)

Deformations of the algebra of quantum operators lead to a description
of fundamental interactions that generalizes (and in a sense unifies)
the principles of gauge theory and the geometric description of gravity
as free fall in curved spacetime. This is quite well established for
electromagnetism and is for example useful for the description of
charged particles in a magnetic monopole background. We shall show that
also gravitational interactions find such an algebraic description, but
the construction requires a graded geometry setting. The construction
suggests a novel somewhat more algebraic interpretation of key
ingredients of general relativity. Generalized Geometry arises in this
context via the derived bracket formalism and yields a symmetry-based
approach to string effective gravity actions. Further examples of
applications of graded geometry and deformation methods in (quantum)
field theory include e.g. non-commutative gauge theory, tensor gauge
theories, non-local interactions.

Wednesday,
30 November 2022

ICMS Lecture Theatre

13:30

A pre-seminar is a session during which speakers will give a short introduction to their talks.

14:30

Romain Ruzziconi
(Vienna University of Technology)

The flat space holography program aims at describing quantum gravity in asymptotically flat spacetime in terms of a dual lower-dimensional field theory. Two different roads to construct flat space holography have recently emerged. The first consists of a 4d bulk / 3d boundary duality, called Carrollian holography, where 4d gravity is suggested to be dual to a 3d Carrollian CFT living on the null boundary of the spacetime. The second is a 4d bulk / 2d boundary duality, called celestial holography, where 4d gravity is dual to a 2d CFT living on the celestial sphere. I will argue that these two seemingly contradictory proposals are actually related. The Carrollian amplitudes will be mapped to the celestial amplitudes using an appropriate integral transform. The Ward identities of the sourced Carrollian CFT, encoding the gravitational flux-balance laws, will be shown to reproduce those of the 2d celestial CFT, encoding the bulk soft theorems.

16:00

Wei Bu
(University of Edinburgh)

Celestial holography is the proposal of a codimension two correspondence between quantum gravity in 4d Minkowski space and some putative celestial conformal field theory on the 2d celestial sphere at the asymptotic boundary of Minkowski space. In this talk, I'll start with what the basics of the correspondence is and how the loop algebra of the wedge algebra of $w_{1+\infty}$ algebra with augmented indices emerges, then move on to review the famous family of W-algebras. After identifying the members of this family that are relevant in the context of celestial holography, I'll describe the physical theory in which W-algebra appears and its derivation.

Wednesday,
16 November 2022

Lecture Theatre 2

14:00

A pre-seminar is a session during which speakers will give a short introduction to their talks.

14:30

Abraham Harte
(Dublin City University)

Every textbook on general relativity states that light propagates along null geodesics. Although there are many senses in which this is true at sufficiently-high frequencies, it breaks down more generally. This talk will focus on the motion "as a whole" of electromagnetic pulses with large (but not infinitely-large) frequencies. Angular momentum then affects the motion, resulting in null but non-geodesic trajectories. Precise answers depend, however, on what exactly is meant by the "pulse as a whole": its centroid. There are many apparently-reasonable centroid definitions, but surprisingly, some of these result in positions which are nowhere near the pulse itself! This turns out to be an unphysical artifact of the fact that electromagnetic wavepackets are only approximately massless. Using this approximation uncritically turns out to result in some predictions which are not even qualitatively correct. The underlying problem is that eikonal approximations break standard features of Maxwell theory, such as the fact that exact electromagnetic stress-energy tensors satisfy positive-energy conditions.

16:00 (Zoom talk)

Roger Penrose
(University of Oxford)

TBA

Wednesday,
2 November 2022

Lecture Theatre 2

13:30

A pre-seminar is a session during which speakers will give a short introduction to their talks.

14:30

Thomas Winyard
(University of Edinburgh)

When an external magnetic field is applied to a superconductor, unlike in a normal metal, the field penetrates the material in localised flux tubes. These flux tubes can be modelled as vortex (topological soliton) solutions of an effective U(1) gauged Ginzburg-Landau (abelian Higgs) model in 2-dimensions with a complex order parameter. The solutions of this model has a rich mathematical structure and understanding their properties has interested mathematicians for several decades.
However, in the hunt for high temperature superconductivity, physicists have recently become interested in unconventional materials that exhibit a C^n order parameter. I will explore the topological soliton solutions of these unconventional models and their properties. I will then demonstrate that doubly periodic solutions exhibit peculiar magnetic structures, finally proposing experimental signatures that could be used to measure these structures in the lab.

16:00

Stefan Prohazka
(University of Edinburgh)

Fractons are quasiparticles with the distinctive feature of having only limited mobility. This bizarre trait and their unusual symmetries also make the coupling to curved spacetime nontrivial. I will highlight the underlying exotic symmetries and show how aristotelian geometry provides the right framework for placing them on curved space.
I will also emphasize that the very definition of isolated fractons requires a careful study of asymptotic symmetries. Analog to electrodynamics and general relativity, fractons have infinitely many soft charges which hint at a rich infrared structure and a fracton infrared triangle.
Based on: 2111.03668, 2203.02817, 2206.11806, work in progress

Wednesday,
19 October 2022

Lecture Theatre 2

14:30

Georgios Papamikos
(University of Essex)

I will be discussing certain dynamical and integrability properties of certain set-theoretical solutions of the (parametric) Yang-Baxter equation. These solutions are bi-rational maps with several invariants and a Lax representation (re-factorisation of two elements of a loop group). We show that we can use these maps to construct higher dimensional bi-rational maps which admit nice properties and we prove their integrability in the Liouville sense. These maps can be seen as higher dimensional generalisations of the famous integrable QRT maps, known as Adler's Triad maps. If we have enough time, we will present two different generalisations, namely the above picture in the case of the entwining Yang-Baxter equation and also for maps with Grassmann variables.

16:00

Alessandro Tomasiello
(Università Milano-Bicocca)

Models with large supersymmetry are unrealistic, but over the years they have proven to be a very fruitful playground for improving our understanding of quantum field theory. In this talk we will consider a new class with eight supercharges in three spacetime dimensions. The simplest example gives a way to enhance the supersymmetry of a model with three Chern--Simons gauge fields (which generically only allows for six supercharges), when the inverses of the levels sums up to zero. We will also see evidence that our class arises by compactifying the mysterious six-dimensional 'M5' model on a three-manifold. Our method reproduces for example the condition for a Seifert manifold to have enhanced holonomy. More generally our class should be related to so-called graph-manifolds. The condition for enhancement is related to a jump in homology groups, and seems to suggest a non-abelian analogue of the theory of 'transversely holomorphic foliations'.

Wednesday,
5 October 2022

Lecture Theatre 2

14:00

A pre-seminar is a session during which speakers will give a short introduction to their talks.

14:30

Joaquim Gomis
(Universitat de Barcelona)

We will study the relation among Galileii dynamical systems, without extensions, and some Carroll dynamical systems. The construction of the Galilei invariant systems will be done from the knowledge of Carroll dynamical models.

16:00

Bin Zhu
(Northeastern University)

In recent years, the surprising relations between asymptotic symmetries and soft theorems have led to a promising candidate for flat holography: celestial holography. The central objects in this program are celestial amplitudes, which behave as correlation functions of primary operators in a putative conformal field theory: celestial CFT (CCFT). In this talk, we will first introduce some basics of celestial amplitudes and CCFT. We then discuss some aspects of celestial amplitudes and CCFT, including operator product expansions (OPEs), how soft theorems are related to symmetries in CCFT, and differential equations for celestial amplitudes. We will describe the recent ideas of top-down approaches in celestial holography and show one specific example, the celestial Liouville theory for Yang-Mills amplitudes. We will conclude with some open questions and future directions.