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

Please contact the organisers Tim Adamo (UoE) or Richard Davison (HW)
with any questions regarding the seminars.

Wednesday,
26 July 2023
at
16:00

7 George Square S.1

Benito Juárez-Aubry
(ICN-UNAM)

Semiclassical gravity is believed to describe the semiclassical regime of quantum gravity, and be relevant in situations sufficiently far from Planck scale where quantum effects and gravity are both important, such as in black holes or cosmology. However, its mathematical and conceptual structure has not been fully understood. In this talk, I describe some advances made in this direction, as well as the challenges that lie ahead and the opportunities that may come from a rigorous understanding of semiclassical gravity, especially in important open questions like the black hole information loss puzzle.

Wednesday,
28 June 2023
at
13:30

7 George Square S.1

Temple He
(Caltech)

Inspired by the second law of thermodynamics, we study the change in subsystem entropy generated by dynamical unitary evolution of a product state in a bipartite system. Working at leading order in perturbative interactions, we prove that the quantum n-Tsallis entropy of a subsystem never decreases, provided that subsystem is initialized as a statistical mixture of states of equal probability. This is true for any choice of interactions and any initialization of the complementary subsystem. When this condition on the initial state is violated, it is always possible to explicitly construct a "Maxwell's demon'' process that decreases the subsystem entropy. Remarkably, for the case of particle scattering, the circuit diagrams corresponding to n-Tsallis entropy are the same as the on-shell diagrams that have appeared in the modern scattering amplitudes program, and the entropy growth is intimately related to the nonnegativity of cross-sections.

Monday,
12 June 2023
at
11:00

José Edelstein
(University of Santiago de Compostela)

General Relativity provides the effective low energy dynamics of gravity. For general reasons, higher curvature corrections are expected. We discuss how these terms may imply a violation of causality (and how to amend it), as well as their relevance in the context of cosmological inflation and black hole accretion.

Wednesday,
24 May 2023

7 George Square S.1

13:00

A session during which speakers will give a short introduction to their talks for PhD students and postdocs.

14:30

Michele del Zotto
(Uppsala)

I will review some recent progress in the context of geometric engineering limits of M-theory and their interplay with higher symmetries of (supersymmetric) field theories.

16:00

Silvia Nagy
(Durham)

I will show that self-dual gravity in Euclidean four-dimensional Anti-de Sitter space (AdS4) can be described by a scalar field with a cubic interaction written in terms of a deformed Poisson bracket, providing a remarkably simple generalisation of the Plebanski action for self-dual gravity in flat space. This implies a novel symmetry algebra in self-dual gravity, notably an AdS4 version of the so-called kinematic algebra. This provides a concrete starting point for defining the double copy for Einstein gravity in AdS4 by expanding around the self-dual sector. Moreover, I will show that the new kinematic Lie algebra can be lifted to a deformed version of the w1+∞ algebra, which plays a prominent role in celestial holography.

Wednesday,
10 May 2023

7 George Square S.1

13:00

A session during which speakers will give a short introduction to their talks for PhD students and postdocs.

14:30

Benoit Vicedo
(University of York)

In recent years various unifying frameworks for understanding 2d integrable field theories have emerged. In this talk I will review the approach based on 4d Chern-Simons theory, due to Costello and Yamazaki, and describe recent progress towards extracting general 2d integrable field theories from 4d Chern-Simons theory.

16:00

Sofia Tarricone
(IPhT Saclay)

In this talk we will study solutions of the cylindrical KdV equation built up by using the Janossy densities of the thinned shifted and dilated Airy determinantal point process. We will see how they can be interpreted as Darboux transformations of known solutions obtained in terms of the Fredholm determinant of the so called finite temperature Airy kernel. Finally we will describe their asymptotic behavior in different regimes. This is based on a joint work with T. Claeys, G. Glesner, G. Ruzza available at ArXiv2303.09848.

Friday,
5 May 2023
at
16:00

7 George Square S.1

Peter Kristel
(Hausdorff Centre, University of Bonn)

In 1987, Killingback considered the spinning string in a manifold M, and determined that if this theory is to be anomaly-free, then the manifold must admit a "string structure". This is in analogy with how a spin structure leads to anomaly cancellation for a spinning point particle. I will explain how to construct the spinor bundle on the loop space of a manifold equipped with a string structure. We will then construct the fusion product on this bundle, which encodes the locality of the theory. This structure (the loop spinor bundle and its fusion product) can be neatly packaged together in a 2-vector bundle on the original manifold, which is a simultaneous generalization of bundle gerbes and algebra bundles.

Wednesday,
26 April 2023

40 George Square Lecture Theatre C

13:00

A session during which speakers will give a short introduction to their talks for PhD students and postdocs.

14:30

Olalla Castro-Alvaredo
(City College London)

In this talk I will introduce some basic ideas about entanglement measures in many-body quantum systems and I will present one of the leading approaches to computing such measures in 1D quantum field theory. This approach is based on relating entanglement measures to correlations functions of a special class of fields called branch point twist fields. Once this connection has been made, the problem of computing entanglement measures is reduced to computing correlation functions, which is generally technically difficult. I will explain how these correlation functions become especially simple for certain types of excited states of quantum field theory and how this simplicity allows us to compute many different measures very explicitly, including a measure that has attracted a lot of interest recently: the symmetry resolved entanglement entropy. My talk contains input from work I have done with many people over the years including Pasquale Calabrese, Luca Capizzi, John L. Cardy, Cecilia De Fazio, Benjamin Doyon, David X. Horváth, Michele Mazzoni, Lucía Santamaría-Sanz and István Szécsény.

16:00

Marcus Sperling
(Shing-Tung Yau Center)

Supersymmetric theories with 8 supercharges in dimensions 3 through 6 have a large moduli space of vacua, and the Higgs branches are one of the most significant parts of this space. These (singular) hyper-Kahler spaces can be characterised by a combinatorial object known as the magnetic quiver. By using this technique, we can fully encode the Higgs branch geometry for both the low energy effective description and the strongly coupled conformal fixed point. A simple algorithm on the magnetic quiver allows us to access the stratification of the Higgs branch, which physically corresponds to the generalised Higgs mechanism. In this talk, I will discuss this construction in the context of 5d and 6d theories.

Wednesday,
12 April 2023

40 George Square Lecture Theatre C

13:00

14:30

Koenraad Schalm
(Leiden)

High Tc cuprate strange metals are noted for a DC-resistivity that scales linearly with T from the onset of superconductivity to the crystal melting temperature, indicative of a Planckian dissipation life time τℏ≃ℏ/(kBT). At the same time, the optical conductivity ceases to be of the Drude form at high temperatures, suggesting a change in dynamics that surprisingly leaves the T-linear DC-resistivity unaffected. We use the AdS/CFT correspondence that describes strongly coupled, densely entangled states of matter to study the DC and optical conductivities of the local quantum critical Gubser-Rocha holographic strange metal in 2+1D in the presence of a lattice potential, a prime candidate to compare with experiment. We find that the DC-resistivity is linear in T at low temperatures for a range of potential strengths and wavevectors, even as it transitions between different dissipative regimes. At weak lattice potential the optical conductivity evolves with temperature from a Drude form to a bad metal characterized by a mid-IR resonance without changing the DC transport, similar to that seen in cuprate strange metals. This mid-IR peak can be understood as a consequence of Umklapp hydrodynamics: i.e. hydrodynamic perturbations are Bloch modes in the presence of a lattice. At strong lattice potential an incoherent metal is realized where momentum conservation no longer plays a role in transport. In this regime the thermal diffusivity appears insensitive to the breaking of translations and can be explained by Planckian dissipation originating in universal microscopic chaos. The charge diffusivity cannot be explained this way, though the continuing linear-in-T DC resistivity saturates to an apparent universal slope, numerically equal to a Planckian rate. We conjecture that this may originate in chaos properties that differ between charged and neutral operators.

16:00

Anne Spiering
(NBI Copenhagen)

The symbol bootstrap has proven to be a powerful tool in the calculation of polylogarithmic Feynman integrals and scattering amplitudes in planar maximally supersymmetric Yang-Mills theory that bypasses the direct integration of loop integrals. In this talk I will discuss a generalisation of this approach to an elliptic case: the symbol bootstrap of the 12-point two-loop double-box integral in four dimensions. The bootstrapping ansatz is obtained from an elliptic generalisation of a Schubert-type analysis of the leading singularities of the double box. After imposing mathematical and physical constraints on this ansatz, one obtains a compact one-line formula for the (2,2)-coproduct of the double-box integral.

Wednesday,
15 March 2023

13:00

14:30

Bernardo Araneda
(AEI Golm)

We propose a twistor description of non-self-dual Kähler metrics and black hole space-times in general relativity. We first focus on complex coordinate transformations between different real solutions, suggesting that they are different real sections of the same complex space. Then we describe how the full non-linear solutions can be understood as deformed twistor quadrics.

16:00

Céline Zwikel
(Perimeter Institute)

I will introduce the partial Bondi gauge for 4 dimensional spacetimes. This partial gauge includes the usual Bondi gauge and Newman-Unti gauge, designed to approach asymptotic boundaries along null rays. This new gauge is only specified by 3 conditions on the metric (g_{rr}=0=g_{rA}). I will discuss the solution space and asymptotic symmetries. Most importantly by relaxing the gauge we uncovered new symmetries of asymptotically flat spacetimes.

Wednesday,
1 March 2023

13:00

14:30

Dionysios Anninos
(King's College London)

We consider theories of gravity where a more "finite" holographic theory is relevant. From a Lorentzian perspective we comment on properties of gravity in the presence of finite timelike boundaries, and holographic realisations. Time permitting, we also discuss Euclidean gravity on manifolds with no boundary, like Euclidean de Sitter.

16:00

Fridrich Valach
(Imperial College London)

I will describe G-algebroids, a class of Leibniz algebroids carrying an "extended inner product", which generalise Lie algebroids, Courant algebroids, and the structures appearing in exceptional geometry. I will show how they provide an efficient tool for the study of consistent truncations of M-theory and type II string theory, and of dualities of the Poisson-Lie type. This is a joint work with M. Bugden, O. Hulik, and D. Waldram.

Wednesday,
15 February 2023
at
16:00

Jules Lamers
(IPhT, CEA Saclay)

The Heisenberg spin chain admits deformations where the spins interact at long distances while remaining quantum integrable / exactly solvable. To understand this family of long-range spin chains it is fruitful to start from a parallel family of quantum many-body systems of Calogero--Sutherland (and Ruijsenaars--Macdonald) type. These models are already quantum integrable / exactly solvable. In particular, in the trigonometric case they are closely related to affine Hecke algebras and, if the particles have spins, enjoy Yangian (respectively quantum-loop) invariance with explicit highest-weight vectors. A special 'freezing' limit produces the long-range spin chains along with their properties. I will start by introducing these two families of models and outlining their properties and connections. Then I will present recent results, work in progress and some open challenges. Based collaborations with R Klabbers (Humboldt U Berlin) and with G Ferrando (Tel Aviv U), F Levkovich-Maslyuk (IPhT) and D Serban (IPhT).

Wednesday,
1 February 2023
at
16:00

Matthew Walters
(EPF Lausanne, University of Geneva)

While quantum field theory has given us a successful description of physical phenomena at many different length scales, almost all computations are currently limited to systems which are weakly-coupled or have large amounts of symmetry. I will present a new theoretical framework for solving general strongly-interacting QFTs, which uses data from UV fixed points (i.e. conformal field theories) to numerically compute QFT observables. This approach uses low-dimension operators from the UV CFT to approximate the low-energy eigenstates of the full QFT Hamiltonian, allowing us to study dynamics even at strong coupling. After presenting a general framework which can be applied to QFTs in any number of dimensions, I will then discuss its application to multiple strongly-coupled systems, focusing in particular on recent results studying non-equilibrium dynamics at finite temperature and the computation of nonperturbative scattering amplitudes.

Wednesday,
25 January 2023

13:00

14:30

Luca Delacretaz
(University of Chicago)

Landau's theory of Fermi liquids is a cornerstone of theoretical physics. I will show how to formulate Fermi liquid theory as an effective field theory of bosonic degrees of freedom, using the mathematical formalism of coadjoint orbits. While at the linear level, this theory reduces to existing multidimensional bosonization approaches, it necessarily features nonlinear corrections that are fixed by the geometry of the Fermi surface. These are crucial to reproduce nonlinear response, such as higher-point functions of currents. The effective field theory framework furthermore systematically parametrizes corrections to Fermi liquid behavior, and provides a computationally advantageous approach for non-Fermi liquids -- strongly interacting fixed points obtained by deforming Fermi liquids with relevant interactions.

16:00

Peter Cameron
(University of Edinburgh)

A spacetime is said to satisfy the Penrose property if every pair of points on past and future null infinity can be connected by a timelike curve. Penrose showed that this property fails in Minkowski spacetime of any dimension but is satisfied in 3+1 dimensional positive mass Schwarzschild. I will consider the Penrose property in more detail and discuss how it is related to the ADM mass and dimensionality of the spacetime. I will then show how some of the ideas arising in the study of this property can be used to prove a version of the positive mass theorem. Finally, I will discuss how the apparent failure of the Penrose property in higher dimensions (regardless of the ADM mass) may be linked to the greater regularity of possible conformal completions of the spacetime at spacelike infinity.

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.