Thu, 19 Jun 2025

16:00 - 17:00
C1

Unusual transport in odd-diffusive systems

Erik Kalz
(University of Potsdam)
Further Information

Erik Kalz is a PhD student at U Potsdam in the group of Ralf Metzler. The group focuses on nonequilibrium statistical physics and anomalous stochastic processes, with applications to biological and soft matter systems.

Abstract

Odd systems, characterised by broken time-reversal or parity symmetry, 
exhibit striking transport phenomena due to transverse responses. In this 
talk, I will introduce the concept of odd diffusion, a generalisation of 
diffusion in two-dimensional systems that incorporates antisymmetric tensor 
components. Focusing on systems of interacting particles, I adapt a 
geometric approach to derive effective transport equations and show how 
interactions give rise to unusual transport in odd systems. I present 
effects like enhanced self-diffusion, reversed Hall drift and even absolute 
negative mobility that solely originate in odd diffusion. These results 
reveal how microscopic symmetry-breaking gives rise to emergent, equilibrium 
and non-equilibrium transport, with implications for soft matter, chiral 
active systems, and topological materials.

 

Thu, 12 Jun 2025

14:30 - 16:00
C1

"Eine grössere Harmonie zwischen Begriff und Bild": Eduard Study on mathematical freedom, language, and objectivity

Nicolas Michel
(Isaac Newton Institute, University of Cambridge & Open University)
Abstract
German mathematician Eduard Study (1862-1930) was an outspoken critic of several emerging trends in modern mathematics at the turn of the century. Intuitionism, he argued, was in the process of eliminating the very notion of truth at the core of any serious scientific endeavour, whereas axiom-obsessed formalists engaged in a mere game of symbols, thereby losing sight of what really grants meaning and value to mathematical concepts. In rejecting both approaches, Study sought to maintain that mathematics was a science formed of freely-created concepts yet still possessed a specific form of objectivity, whose exploration crucially relied on the careful construction of symbolic languages.
 
To disentangle these claims, this talk will delve into Study's unpublished, philosophical essay on the foundations of analysis, and compare it to the mathematical practice espoused in his 1903 Geometrie der Dynamen, a landmark volume in the history of kinematics.
Wed, 21 May 2025
12:00
C1

On the converse of Pansu’s differentiability theorem

Andrea Merlo
(Universidad del País Vasco)
Abstract

In this talk I will present two new results concerning differentiability of Lipschitz maps between Carnot groups. The former is a suitable adaptation of Pansu-Rademacher differentiability theorem to general Radon measures. More precisely we construct a suitable bundle associated to the measure along which Lipschitz maps are differentiable, very much in the spirit of the results of Alberti-Marchese. The latter is the converse of Pansu’s theorem. Namely, let G be a Carnot group and μ a Radon measure on G. Suppose further that every Lipschitz map between G and H, some other Carnot group, is Pansu differentiable μ-almost everywhere. We show that μ must be absolutely continuous with respect to the Haar measure of G. This is a joint work with Guido De Philippis, Andrea Marchese, Andrea Pinamonti and Filip Rindler.

This new sub-Riemannian result will be an excuse to present and discuss the techniques employed in Euclidean spaces to prove the converse of Rademacher's theorem.

Wed, 30 Apr 2025
15:30
C1

Uniqueness of gauge covariant renormalisation of stochastic 3D Yang-Mills

Ilya Chevyrev
(University of Edinburgh)
Abstract

In this talk, I will describe a family of observables for 3D quantum Yang-Mills theory based on regularising connections with the YM heat flow. I will describe how these observables can be used to show that there is a unique renormalisation of the stochastic quantisation equation of YM in 3D that preserves gauge symmetries. This complements a recent result on the existence of such a renormalisation. Based on joint work with Hao Shen.

Tue, 24 Jun 2025
16:00
C1

From directed graphs of groups to Kirchberg algebras

Victor Wu
(University of Sydney)
Abstract

Directed graph algebras have long been studied as tractable examples of C*-algebras, but they are limited by their inability to have torsion in their K_1 group. Graphs of groups, which are famed in geometric group theory because of their intimate connection with group actions on trees, are a more recent addition to the C*-algebra scene. In this talk, I will introduce the child of these two concepts – directed graphs of groups – and describe how their algebras inherit the best properties of its parents’, with a view to outlining how we can use these algebras to model a class of C*-algebras (stable UCT Kirchberg algebras) which is classified completely by K-theory.

Thu, 05 Dec 2024

11:00 - 12:00
C1

Local-Global Principles and Fields Elementarily Characterised by Their Absolute Galois Groups

Benedikt Stock
(University of Oxford)
Abstract

Jochen Koenigsmann’s Habilitation introduced a classification of fields elementarily characterised by their absolute Galois groups, including two conjecturally empty families. The emptiness of one of these families would follow from a Galois cohomological conjecture concerning radically closed fields formulated by Koenigsmann. A promising approach to resolving this conjecture involves the use of local-global principles in Galois cohomology. This talk examines the conceptual foundations of this method, highlights its relevance to Koenigsmann’s classification, and evaluates existing local-global principles with regard to their applicability to this conjecture.

Thu, 27 Jun 2024

15:15 - 16:15
C1

Cartan subalgebras of twisted groupoid $C^*$-algebras with a focus on $k$-graph $C^*$-algebras

Rachael Norton
(St Olaf College)
Abstract

The set $M_n(\mathbb{R})$ of all $n \times n$ matrices over the real numbers is an example of an algebraic structure called a $C^*$-algebra. The subalgebra $D$ of diagonal matrices has special properties and is called a \emph{Cartan subalgebra} of $M_n(\mathbb{R})$. Given an arbitrary $C^*$-algebra, it can be very hard (but also very rewarding) to find a Cartan subalgebra, if one exists at all. However, if the $C^*$-algebra is generated by a cocycle $c$ and a group (or groupoid) $G$, then it is natural to look within $G$ for a subgroup (or subgroupoid) $S$ that may give rise to a Cartan subalgebra. In this talk, we identify sufficient conditions on $S$ and $c$ so that the subalgebra generated by $(S,c)$ is indeed a Cartan subalgebra of the $C^*$-algebra generated by $(G,c)$. We then apply our theorem to $C^*$-algebras generated by $k$-graphs, which are directed graphs in higher dimensions. This is joint work with J. Briones Torres, A. Duwenig, L. Gallagher, E. Gillaspy, S. Reznikoff, H. Vu, and S. Wright.

Fri, 28 Jun 2024

15:00 - 16:00
C1

Permanence of Structural properties when taking crossed products

Dawn Archey
(University of Detroit Mercy)
Abstract

 Structural properties of C*-Algebras such as Stable Rank One, Real Rank Zero, and radius of comparison have played an important role in classification.  Crossed product C*-Algebras are useful examples to study because knowledge of the base Algebra can be leveraged to determine properties of the crossed product.  In this talk we will discuss the permanence of various structural properties when taking crossed products of several types.  Crossed products considered will include the usual C* crossed product by a group action along with generalizations such as crossed products by a partial automorphism.  

This talk is based on joint work with Julian Buck and N. Christopher Phillips and on joint work with Maria Stella Adamo, Marzieh Forough, Magdalena Georgescu, Ja A Jeong, Karen Strung, and Maria Grazia Viola.

Thu, 27 Jun 2024

16:30 - 17:30
C1

The Zappa–Szép product of groupoid twists

Anna Duwenig
(KU Leuven)
Abstract

The Zappa–Szép (ZS) product of two groupoids is a generalization of the semi-direct product: instead of encoding one groupoid action by homomorphisms, the ZS product groupoid encodes two (non-homomorphic, but “compatible”) actions of the groupoids on each other. I will show how to construct the ZS product of two twists over such groupoidand give an example using Weyl twists from Cartan pairs arising from Kumjian--Renault theory.

 Based on joint work with Boyu Li, New Mexico State University

Subscribe to C1