Oct 17 (Fri)
13:00 MCS0001 HEPMNeil Lambert (King's College London): Quantum and Classical Properties of the Sen Acton for Self-Dual Fields
Sen has proposed a novel action for self-dual fields that has been generalised by Hull to include two metrics. The resulting theory has many novel features including two independent diffeomorphism-like symmetries. Furthermore the action is quadratic in the fields and as a result the path-integral can be can be computed. We will discuss various aspect of this theory in two-dimensions such as the partition function and modular invariance.
Venue: MCS0001
Oct 20 (Mon)
13:00 MCS3070 ApplLian Gan (Durham (Engineering)): Vortex rings with weak to moderate swirl
The formation of swirling vortex rings and their early time evolution, resulting from the controlled discharge of an incompressible, Newtonian fluid into a stationary equivalent fluid bulk, is explored for weak to moderate swirl number 0≤𝑆≤1 . We first investigated rings generated by idealised solid-body rotation simultaneously superposed onto a linear momentum discharge in two commonly encountered inlet conditions in practice using LES simulations. The results obtained reveal that, for 𝑆≥0.5 , the addition of swirl promotes the breakdown of the leading primary vortex ring structure, giving rise to the striking feature of significant negative azimuthal vorticity generation in the region surrounding the primary vortex ring core, whose strength scales with 𝑆2. We subsequently evaluated the characteristics of swirling vortex rings generated in laboratory by a physical rotating tube using PIV. Experiments without linear discharge (tube rotation preparation stage without rings being produced) reveal the presence of an intriguing secondary flow pattern in the rotating tube, preventing attainment of a solid-body like swirl distribution. A key feature of the experimental work is that partially established vortex rings, produced with short tube rotation preparation time before a steady state condition is reached, show unique characteristics. Their creation, a short time after the onset of tube rotation: (i) facilitates more efficient delivery of swirl momentum to the vortex core area; (ii) maintains a low level of swirl in the ring bubble's central region which would otherwise promote the formation of opposite-signed vorticity and vortex breakdown.
Venue: MCS3070
Online: https://teams.microsoft.com/l/meetup-join/19%3ameeting_YWEyMjFhNWQtOTlkNi00N2Y3LTg1ZjQtNTA5NDNkMzJmZWZm%40thread.v2/0?context=%7b%22Tid%22%3a%227250d88b-4b68-4529-be44-d59a2d8a6f94%22%2c%22Oid%22%3a%2246d8fe9f-6805-46f3-9ece-8a80837320a9%22%7d
14:00 MCS2068 PureDawid Kielak (Oxford): Virtual Fibring of manifolds and groups
I will discuss the problem of recognising when a given (aspherical) manifold admits a finite cover that fibres over the circle. This problem is intimately connected to properties of the fundamental group. I will also discuss a group-theoretic variant, namely algebraic fibring of Poincare-duality groups.
Venue: MCS2068
Oct 21 (Tue)
13:00 MCS2068 APDECodina Cotar (University College London): Some new results on non-convex random gradient Gibbs measures
In this talk we consider a class of gradient models with and without disorder. The simplest example of such models is the (lattice) Gaussian Free Field, which has quadratic potential V(s)=s^2/2. A well
known result of Funaki and Spohn asserts that, for any uniformly-convex potential V, the possible
infinite-volume measures of this type are uniquely characterized by the tilt, which is a vector in R^d. We show that this model is disorder relevant with respect to the question of uniqueness of gradient Gibbs measures when disorder is added to the system. We also discuss some functional inequalities connected to the model (such as Poincaré, log-Sobolev). No previous knowledge of gradient models will be assumed in the talk. This is based on joint works with Simon Buchholz and Florian Schweiger.
Venue: MCS2068
14:00 MCS2068 ASGColton Griffin (University of Pennsylvania): Higher-dimensional vertex algebras
Vertex (operator) algebras were originally defined by Borcherds and Frenkel-Lepowksy-Meurman in the study of the monster group and affine Lie algebras, taking inspiration from bosonic string theory. Since their inception, they have been shown to be closely related to modular forms, geometric Langlands, and the moduli space of stable pointed curves. More specifically, one may use these objects to construct sheaves of coinvariants on the moduli space of stable complex curves. Under certain niceness assumptions, these sheaves are induced by vector bundles with explicit formulae for their Chern classes using the representation theory of vertex algebras. On their own, vertex algebras are intricate objects to study from a representation-theoretic perspective as well.
With such rich structure for curves, it is natural to ask if there are vertex algebraic analogues suitable for the study of higher-dimensional geometric objects. We describe a family of such analogues, which we call “cohomological vertex algebras.” These are obtained by replacing Laurent series in the definition of a vertex algebra with the Čech cohomology of schemes modeling infinitesimal neighborhoods in higher-dimensional spaces.
We will start by motivating the definition of a vertex algebra and its many axioms from a non-geometric perspective; after doing so, we will describe how to modify the definition to obtain cohomological vertex algebras. Time permitting, we will then discuss the construction of coinvariants and conformal blocks on higher-dimensional varieties.
Venue: MCS2068
Oct 23 (Thu)
13:00 MCS2068 G&TJohn Parker (Durham University): Real hyperbolic on the outside, complex hyperbolic on the inside (1)
The title of the talk is the title of a paper by Richard Schwartz (Inventiones 2003) where he constructs a complex hyperbolic orbifold whose boundary is homeomorphic to a closed real hyperbolic three-manifold. The fundamental group of the orbifold is an index two subgroup of a group generated by three reflections where certain products of the reflections have particular finite orders. The proof is by way of an explicit construction of a fundamental polyhedron. In these talks I will discuss a joint project with Yohei Komori and Makoto Sakuma where we take the first step to generalise Schwartz’s construction. Namely, we give a topological construction of a candidate fundamental domain, and thereby we are able to describe the topology of the boundary manifold explicitly in terms of the finite orders of the products of reflections. In particular, we are able to topologically identify Schwartz’s boundary manifold.
Venue: MCS2068
14:00 MCS2068 ProbJoão de Oliveira Madeira (University of Oxford): How Can Seed Banks Evolve in Plants? A Stochastic Dynamics Approach
In this talk, we study how varying environmental conditions influence the evolution of seed banks in plants. Our model is a modification of the WrightFisher model with finite-age seed bank, introduced by Kaj, Krone and Lascoux. We distinguish between wild type individuals, producing only nondormant seeds, and mutants, producing seeds with finite dormancy. To understand how environments shape the establishment of seed banks, we analyse the process under diffusive scaling. The results support the biological insight that seed banks are favoured under adverse and fluctuating environments. Mathematically, our analysis reduces to a stochastic dynamical system forced onto a manifold by a large drift, which converges under scaling to a diffusion on the manifold. By projecting the system onto its linear counterpart, we derive an explicit formula for the limiting diffusion coefficients. This provides a general framework for deriving diffusion approximations in models with strong drift and nonlinear constraints. This is a joint work with Alison Etheridge.
Venue: MCS2068
Oct 24 (Fri)
13:00 MCS0001 HEPMNicola Dondi (ICTP Trieste): TBA
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Usual Venue: MCS2068
Contact: yohance.a.osborne@durham.ac.uk
Oct 21 13:00 Codina Cotar (University College London): Some new results on non-convex random gradient Gibbs measures
In this talk we consider a class of gradient models with and without disorder. The simplest example of such models is the (lattice) Gaussian Free Field, which has quadratic potential V(s)=s^2/2. A well
known result of Funaki and Spohn asserts that, for any uniformly-convex potential V, the possible
infinite-volume measures of this type are uniquely characterized by the tilt, which is a vector in R^d. We show that this model is disorder relevant with respect to the question of uniqueness of gradient Gibbs measures when disorder is added to the system. We also discuss some functional inequalities connected to the model (such as Poincaré, log-Sobolev). No previous knowledge of gradient models will be assumed in the talk. This is based on joint works with Simon Buchholz and Florian Schweiger.
Venue: MCS2068
Usual Venue: MCS3070
Contact: andrew.krause@durham.ac.uk
Oct 20 13:00 Lian Gan (Durham (Engineering)): Vortex rings with weak to moderate swirl
The formation of swirling vortex rings and their early time evolution, resulting from the controlled discharge of an incompressible, Newtonian fluid into a stationary equivalent fluid bulk, is explored for weak to moderate swirl number 0≤𝑆≤1 . We first investigated rings generated by idealised solid-body rotation simultaneously superposed onto a linear momentum discharge in two commonly encountered inlet conditions in practice using LES simulations. The results obtained reveal that, for 𝑆≥0.5 , the addition of swirl promotes the breakdown of the leading primary vortex ring structure, giving rise to the striking feature of significant negative azimuthal vorticity generation in the region surrounding the primary vortex ring core, whose strength scales with 𝑆2. We subsequently evaluated the characteristics of swirling vortex rings generated in laboratory by a physical rotating tube using PIV. Experiments without linear discharge (tube rotation preparation stage without rings being produced) reveal the presence of an intriguing secondary flow pattern in the rotating tube, preventing attainment of a solid-body like swirl distribution. A key feature of the experimental work is that partially established vortex rings, produced with short tube rotation preparation time before a steady state condition is reached, show unique characteristics. Their creation, a short time after the onset of tube rotation: (i) facilitates more efficient delivery of swirl momentum to the vortex core area; (ii) maintains a low level of swirl in the ring bubble's central region which would otherwise promote the formation of opposite-signed vorticity and vortex breakdown.
Venue: MCS3070
Usual Venue: MCS2068
Contact: herbert.gangl@durham.ac.uk
Oct 21 14:00 Colton Griffin (University of Pennsylvania): Higher-dimensional vertex algebras
Vertex (operator) algebras were originally defined by Borcherds and Frenkel-Lepowksy-Meurman in the study of the monster group and affine Lie algebras, taking inspiration from bosonic string theory. Since their inception, they have been shown to be closely related to modular forms, geometric Langlands, and the moduli space of stable pointed curves. More specifically, one may use these objects to construct sheaves of coinvariants on the moduli space of stable complex curves. Under certain niceness assumptions, these sheaves are induced by vector bundles with explicit formulae for their Chern classes using the representation theory of vertex algebras. On their own, vertex algebras are intricate objects to study from a representation-theoretic perspective as well.
With such rich structure for curves, it is natural to ask if there are vertex algebraic analogues suitable for the study of higher-dimensional geometric objects. We describe a family of such analogues, which we call “cohomological vertex algebras.” These are obtained by replacing Laurent series in the definition of a vertex algebra with the Čech cohomology of schemes modeling infinitesimal neighborhoods in higher-dimensional spaces.
We will start by motivating the definition of a vertex algebra and its many axioms from a non-geometric perspective; after doing so, we will describe how to modify the definition to obtain cohomological vertex algebras. Time permitting, we will then discuss the construction of coinvariants and conformal blocks on higher-dimensional varieties.
Venue: MCS2068
Nov 04 14:00 Yu-Chen Sun (University of Bristol):
Nov 11 14:00 Robin Bartlett (University of Glasgow):
Nov 25 14:00 Dante Luber (Queen Mary University of London): Matroid theory, algebra, and computation
Matroids combinatorially abstract independence properties of
finite dimensional linear algebra. They have become ubiquitous in
modern mathematics, and yield connections between graph theory,
algebra, polyhedral geometry, optimization, and beyond. Special
matroids capture the properties of point line arrangementments in
complex 2-projective space. The moduli space of all line arrangements
corresponding to a matroid is known as its realization space. After an
introduction to matroid theory, we will discuss how we have used the
OSCAR software system to study large datasets of matroids, isolating
examples whose realization spaces have interesting algebro-geometric
Venue: MCS2068
Dec 02 14:00 Jay Taylor (University of Manchester):
Dec 09 14:00 Fredrik Stromberg (University of Nottingham):
Usual Venue: OC218
Contact: mohamed.anber@durham.ac.uk
For more information, see HERE.
No upcoming seminars have been scheduled (not unusual outside term time).
Usual Venue: MCS3052
Contact: andrew.krause@durham.ac.uk
No upcoming seminars have been scheduled (not unusual outside term time).
Usual Venue: MCS2068
Contact: fernando.galaz-garcia@durham.ac.uk
Oct 23 13:00 John Parker (Durham University): Real hyperbolic on the outside, complex hyperbolic on the inside (1)
The title of the talk is the title of a paper by Richard Schwartz (Inventiones 2003) where he constructs a complex hyperbolic orbifold whose boundary is homeomorphic to a closed real hyperbolic three-manifold. The fundamental group of the orbifold is an index two subgroup of a group generated by three reflections where certain products of the reflections have particular finite orders. The proof is by way of an explicit construction of a fundamental polyhedron. In these talks I will discuss a joint project with Yohei Komori and Makoto Sakuma where we take the first step to generalise Schwartz’s construction. Namely, we give a topological construction of a candidate fundamental domain, and thereby we are able to describe the topology of the boundary manifold explicitly in terms of the finite orders of the products of reflections. In particular, we are able to topologically identify Schwartz’s boundary manifold.
Venue: MCS2068
Oct 30 13:00 John Parker (Durham University): Real hyperbolic on the outside, complex hyperbolic on the inside (2)
The title of the talk is the title of a paper by Richard Schwartz (Inventiones 2003) where he constructs a complex hyperbolic orbifold whose boundary is homeomorphic to a closed real hyperbolic three-manifold. The fundamental group of the orbifold is an index two subgroup of a group generated by three reflections where certain products of the reflections have particular finite orders. The proof is by way of an explicit construction of a fundamental polyhedron. In these talks I will discuss a joint project with Yohei Komori and Makoto Sakuma where we take the first step to generalise Schwartz’s construction. Namely, we give a topological construction of a candidate fundamental domain, and thereby we are able to describe the topology of the boundary manifold explicitly in terms of the finite orders of the products of reflections. In particular, we are able to topologically identify Schwartz’s boundary manifold.
Venue: MCS2068
Nov 13 13:00 Pierre Will (Université Grenoble Alpes): TBA
Nov 20 13:00 Amy Herron (University of Bristol): Triangle Presentations in ~A_2 Bruhat-Tits Buildings
The 1-skeleton of an ~A_2 Bruhat-Tits building is isomorphic to the Cayley graph of an abstract group with relations coming from triangle presentations. This abstract group either embeds into PGL(3, Fq((x))) or PGL(3, Qq), or else is exotic. Currently, the complete list of triangle presentations is only known for projective planes of orders q=2 or 3. However, one abstract group that embeds into PGL(3,Fq((x))) for any prime power q is known via the trace function corresponding to the finite field of order q^3. I found a new method to derive this group via perfect difference sets. This method demonstrates a previously unknown connection between difference sets and ~A_2 buildings. Moreover, this method makes the final computation of triangle presentations easier, which is computationally valuable for large q.
Venue: MCS2068
Nov 27 13:00 Yan Rybalko (University of Oslo): Generic regularity of the two-component Novikov system
In my talk I will discuss the generic regularity of the Cauchy problem for the two-component Novikov system. This system is integrable (i.e., it is bi-Hamiltonian, has a Lax pair, and an infinite number of conservation laws), and admits peakon solutions of the form p(t)exp(-|x-q(t)|). Another important feature of the Novikov system is the wave-breaking phenomenon: the solutions remain bounded for all times, but the slope can blow-up in finite time. In our work, we show that there exists an open dense subset of C^k regular initial data, such that the corresponding global solutions persist the regularity for all t,x except, possibly, a finite number of piecewise C^{k-1} characteristic curves. Our approach builds on the work by Bressan and Chen, which relies on transforming solutions from Eulerian variables to a new set of Bressan-Constantin variables, in which all possible singularities of the original solutions are resolved. Then, applying the Thoms transversality theorem to the map related to the wave-breaking, we can construct an appropriate open dense subset of C^k regular initial data.
The talk is based upon the following papers:
K.H. Karlsen, Ya. Rybalko, "Generic regularity and a Lipschitz metric for the two-component Novikov system," in preparation.
K.H. Karlsen, Ya. Rybalko, "Global semigroup of conservative weak solutions of the two-component Novikov equation," Nonlinear Analysis: Real World Applications 86, 104393 (2025). DOI: 10.1016/j.nonrwa.2025.104393.
Venue: MCS2068
Jan 22 13:00 Chunyang Hu (Durham University): TBA
Mar 06 13:00 Julian Scheuer (Goethe University Frankfurt): TBA
Usual Venue: MCS0001
Contact: p.e.dorey@durham.ac.uk,enrico.andriolo@durham.ac.uk,tobias.p.hansen@durham.ac.uk
Oct 17 13:00 Neil Lambert (King's College London): Quantum and Classical Properties of the Sen Acton for Self-Dual Fields
Sen has proposed a novel action for self-dual fields that has been generalised by Hull to include two metrics. The resulting theory has many novel features including two independent diffeomorphism-like symmetries. Furthermore the action is quadratic in the fields and as a result the path-integral can be can be computed. We will discuss various aspect of this theory in two-dimensions such as the partition function and modular invariance.
Venue: MCS0001
Oct 24 13:00 Nicola Dondi (ICTP Trieste): TBA
Oct 31 13:00 Max Hutt (Imperial College London): TBA
Nov 07 13:00 Stathis Vitouladitis (Université Libre de Bruxelles): Entanglement asymmetry and the limits of symmetry breaking
Entanglement asymmetry is a novel diagnostic of symmetry breaking, rooted in quantum information theory, particularly effective at capturing such effects within subsystems. In this talk, I will first introduce this observable, outline recent developments, and then generalise it to higher-form symmetries, with applications to topological phases and systems with continuous symmetry breaking. As a main application, I will establish an entropic Mermin-Wagner-Coleman theorem, valid for both 0-form and higher-form symmetries, and extended to subregions. These entropic theorems not only detect but also quantify symmetry breaking. In Goldstone phases (when allowed), the Rényi and entanglement asymmetries, increase monotonically with subregion size. Along the way, I will clarify subtleties in defining and computing entanglement asymmetry by Euclidean path integral methods and present standalone results on the entanglement entropy of gauge fields.
Venue: MCS0001
Nov 14 13:00 Christian Copetti (Oxford): TBA
Nov 21 13:00 Ida Zadeh (Southampton): TBA
Nov 28 13:00 Tim Meier (Santiago de Compostela): TBA
Dec 05 13:00 Marco Meineri (Torino): TBA
Dec 12 13:00 Sungwoo Hong (KAIST, Taejon): TBA
Usual Venue: MCS2068
Contact: tyler.helmuth@durham.ac.uk,oliver.kelsey-tough@durham.ac.uk
Oct 23 14:00 João de Oliveira Madeira (University of Oxford): How Can Seed Banks Evolve in Plants? A Stochastic Dynamics Approach
In this talk, we study how varying environmental conditions influence the evolution of seed banks in plants. Our model is a modification of the WrightFisher model with finite-age seed bank, introduced by Kaj, Krone and Lascoux. We distinguish between wild type individuals, producing only nondormant seeds, and mutants, producing seeds with finite dormancy. To understand how environments shape the establishment of seed banks, we analyse the process under diffusive scaling. The results support the biological insight that seed banks are favoured under adverse and fluctuating environments. Mathematically, our analysis reduces to a stochastic dynamical system forced onto a manifold by a large drift, which converges under scaling to a diffusion on the manifold. By projecting the system onto its linear counterpart, we derive an explicit formula for the limiting diffusion coefficients. This provides a general framework for deriving diffusion approximations in models with strong drift and nonlinear constraints. This is a joint work with Alison Etheridge.
Venue: MCS2068
Nov 20 14:00 PiNE (University of Edinburgh): No seminar PiNE in Edinburgh.
PiNE will take place in Edinburgh, see https://www.maths.dur.ac.uk/PiNE/25-11-20/index.html. Accordingly we will not have a seminar this week.
Venue: MCS2068
Usual Venue: MCS2068
Contact: michael.r.magee@durham.ac.uk
Oct 20 14:00 Dawid Kielak (Oxford): Virtual Fibring of manifolds and groups
I will discuss the problem of recognising when a given (aspherical) manifold admits a finite cover that fibres over the circle. This problem is intimately connected to properties of the fundamental group. I will also discuss a group-theoretic variant, namely algebraic fibring of Poincare-duality groups.
Venue: MCS2068
Nov 17 14:00 Pierre Will (Grenoble): TBA
Dec 01 14:00 Brian Petri (Jussieu): TBA
Dec 08 14:00 Stuart White (Oxford): TBA
Usual Venue: MCS3070
Contact: joe.thomas@durham.ac.uk
No upcoming seminars have been scheduled (not unusual outside term time).