Math Calendar

Tuesday, March 5, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
Remy van Dobben de Bruyn - Class field theory for topologists

The goal of class fieldtheory is to compute the abelianisation of the absolute Galois group of aglobal or local field. Since the 1950s, the proofs are carried out entirely inthe language of Galois cohomology, consisting of a formal part ('abstract classfield theory') and a few (long) computations. I will give an introduction tothe area and explain the formal part of the story, using the formalism of Mackeyfunctors from equivariant stable homotopy theory.

Freudenthal topology seminar
16:00-17:00
HFG 611
MI talk
Younghan Bae - Moduli spaces of curves, line bundles and abelian varieties
Moduli spaces of smooth, or stable nodal, curves have been an important subject of algebraic geometry, topology, and mathematical physics. There is a natural way to relate this moduli space with the moduli space of abelian varieties. Over the moduli space of smooth curves M_g, the relative Picard scheme gives a family of principally polarized abelian varieties (p.p.a.v.). Taking this perspective, one can obtain many interesting results on M_g. When curves degenerate into nodal curves, the relative Picard scheme is no longer compact. One can compactly such family and get relative compactified Picard schemes which is no longer a family of p.p.a.v This geometry brings many new geometry and topology. I will try to introduce some new questions on this direction. It will be a gentle overview of a lecture series which I will deliver this block.
 
Seminar webpage https://utrechtgeometrycentre.nl/ugc-seminar/
Thursday, March 7, 2024
10:00-11:00
BBG 061
AG Seminar talk
Ana María Botero - tbd
Abstract: tbd
16:00-17:00
HFG 611
MI Talk Tristan van Leeuven







Talk: Uncertainty Quantification in Large-Scale Inverse Problems — Challenges and Opportunities

Abstract: In an inverse problem, one tries to infer the cause of a measured effect. Such problems are ubiquitous in science and engineering, and well-known examples include medical imaging and non-destructive testing. The basic approach is to fit a parametrised mathematical model of the underlying process to measurements, using (non-linear) optimisation techniques. Mathematical analysis tells us that such problems are often ill-posed, and additional prior information is needed to make the problem well-posed. Casting this in a Bayesian framework then allows us to quantify uncertainty (UQ) in the resulting estimates. Computing these uncertainties is still a challenge for large-scale applications. Research in the past few years aims to exploit advances in machine learning (ML) and the abundance of available (training) data to solve inverse problems more efficiently and more accurately. With such data-driven techniques the line between the model and prior information is blurring, and one of the challenges is to incorporate the known physics of the system in traditional black-box ML models. In this talk, I will give an overview of some of the recent developments in this area and present results on Bayesian UQ in medical imaging with normalising flows.

Tuesday, March 12, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
Christian Carrick - TBA
Thursday, March 14, 2024
16:00-17:00
HFG 611
Applied Math Seminar
Hildeberto Kojakhmetov (RUG)
Friday, March 15, 2024
14:00-16:30
Amsterdam NU building 9-A46
DDT&G
Francesco Lin – Topology of the Dirac equation on spectrally large three-manifolds
In the first talk, I will review the classical work of Atiyah and Singer describing the homotopy type of the family of Dirac operators on a spin Riemannian manifold, and its consequences regarding metrics of positive scalar curvature. In the second talk, I will discuss how one can exploit the Seiberg-Witten equations and Floer theory to obtain more detailed information about the structure of the family in the case of a three-manifold for which the spectral gap of the Hodge Laplacian on coexact 1-forms is large compared to the curvature. For concreteness, we will have a special focus on the case of the n-torus throughout the talks.
Tuesday, March 19, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
Sven van Nigtevecht - TBA
13:00-13:45
KBG Cosmos
Arakelov Theory seminar
TBA - Relative degree 0 case
14:00-14:45
KBG Cosmos
Arithmetic geometry talk
Lara Vicino (Groningen) - TBA
TBA
15:20-16:10
KBG Cosmos
Arithmetic geometry talk
Tian Wang (Bonn) - TBA
TBA
16:00-17:00
HFG 611
UGC seminar
Michel van Garrel (Birmingham) - TBA
16:25-17:15
KGB Cosmos
Arithmetic geometry talk
Yotam Hendel (Leuven) - TBA
TBA
Thursday, March 21, 2024
10:00-11:00
HFG 409
AG Seminar talk
Ratko Darda -
Abstract: tbd
Tuesday, March 26, 2024
10:00-11:00
MIN 0.13
AG Seminar talk
Younghan Bae -
Abstract: tbd
12:00-13:00
HFG 610
Freudenthal topology seminar
Ryan Quinn - TBA
16:00-17:00
HFG 611
MI talk
Thorsten Schimannek - TBA
Thursday, March 28, 2024
10:00-11:00
BBG 061
AG Seminar talk
Younghan Bae -
Abstract: tbd
Tuesday, April 2, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
TBA - TBA
Thursday, April 4, 2024
10:00-11:00
KBG 224
AG Seminar talk
Sara Mehidi -
Abstract: tbd
16:00-17:00
HFG 611
Applied Math Seminar
Arkadi Predtetchinski (Maastricht) Zero-one Laws for a Control Problem with Random Action Sets

In many control problems there is only limited information about the actions that will be available at future stages. We introduce a framework where the Controller sequentially chooses actions $a_{0}, a_{1}, \ldots$, one at a time. Her goal is maximize the probability that the infinite sequence $(a_{0}, a_{1}, \ldots)$ is an element of a given subset $G$ of $\N^\N$. The set $G$ is assumed to be a Borel tail set. The Controller's choices are restricted: having taken a sequence $h_{t} = (a_{0}, \ldots, a_{t-1})$ of actions prior to stage $t \in \N$, she must choose an action $a_{t}$ at stage $t$ from a non-empty, finite subset $A(h_{t})$ of $\N$. The set $A(h_{t})$ is chosen from a distribution $p_{t}$, independently over all $t \in \N$ and all $h_{t} \in \N^{t}$. We consider several information structures defined by how far ahead into the future the Controller knows what actions will be available.

In the special case where all the action sets are singletons (and thus the Controller is a dummy), Kolmogorov’s 0-1 law says that the probability for the goal to be reached is 0 or 1. We construct a number of counterexamples to show that in general the value of the control problem can be strictly between 0 and 1, and derive several sufficient conditions for the 0-1 ``law" to hold.

JOINT WORK WITH: J\'{a}nos Flesch, William Sudderth, Xavier Venel

Friday, April 5, 2024
11:00-16:00
Mark Kac seminar in mathematical physics and probability
Giulia Sebastiani and Adrien Schertzer (U Frankfurt) and Vittoria Silvestri (U Rome)

 A CRASH COURSE ON MEAN FIELD MODELS: DERRIDA’S GREM AND APPLICATIONS

Part 5 - On the GREM Approximation of TAP Free Energies. By Giulia Sebastiani.
The free energy of TAP-solutions for the SK-model of mean field spin glasses can be expressed as a nonlinear functional of local terms: 
we exploit this feature in order to contrive abstract GREM-like models which we then solve by a classical large deviations treatment. 
This allows to identify the origin of the physically unsettling quadratic (in the inverse of temperature) correction to the Parisi free energy 
for the SK-model, and formalizes thetrue cavity dynamics which acts on TAP-space, i.e. on the space of TAP-solutions. 
Joint works with Nicola Kistler, and Marius A. Schmidt. 

Part 6 - From log-correlated models to (un)directed polymers in the mean field limit. By Adrien Schertzer. 
As seen in the previous lectures, Derrida's Random Energy Models have played a key role in the understanding of certain issues in spin glasses. 
The mathematical analysis of these models -  in particular the multi-scale refinement of the second moment method as devised by Kistler, 
is also particularly efficient to analyse the so-called log-correlated class; the latter consists of Gaussian fields with - as the name suggests, 
logarithmically decaying correlations. I will introduce/recall some models falling into this class, and the main steps in their analysis 
through the paradigmatic Branching Brownian motion / Branching Random Walk. Finally, I will conclude with recent results on models 
which are not even Gaussian, but for which the multiscale treatment still goes through swiftly: 
the directed and undirected first passage percolation in the limit of large dimensions, a.k.a. the (un)directed polymers in random environment.
Joint works with Nicola Kistler, and Marius A. Schmidt.
Tuesday, April 9, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
Gijs Heuts - TBA
16:00-17:00
HFG - 611
UGC seminar
Chris Keyes (King's College London) - TBA
Thursday, April 11, 2024
10:00-11:00
BBG 017
AG Seminar talk
Younghan Bae -
Abstract: tbd
Tuesday, April 16, 2024
16:00-17:00
HFG 611
Number Theory Talk
Jakob Glas (IST Austria) - TBA
Thursday, April 18, 2024
10:00-11:00
BBG 017
AG Seminar talk
Andrea Ricolfi -
Abstract: tbd
Tuesday, April 23, 2024
12:00-13:00
HFG 610
Freudenthal topology seminar
Léonard Guetta - TBA
16:00-17:00
HFG 611
MI talk
Dirk van Bree - TBA
Thursday, April 25, 2024
16:00-17:00
HFG 611
Applied Math Seminar
Andrei Caragea (MIDS, Katholische Universität Eichstätt)
Title: TBA
Abstract: TBA
Friday, April 26, 2024
14:00-16:30
DDT&G
Luciana Basualdo Bonatto – TBA
Thursday, May 2, 2024
16:00-17:00
HFG 611
Applied Math Seminar
János Flesch (Maastricht) for May 2, Equilibrium in stochastic games with Borel measurable evaluations
Tuesday, May 28, 2024
16:00-17:00
HFG 611
UGC Seminar
Raymond Cheng (Hannover) - TBA
Thursday, June 6, 2024
16:00-17:00
HFG 611
Applied Math Seminar
Bernhard von Stengel (London School of Economics)
Friday, June 7, 2024
11:00-16:00
Mark Kac seminar in mathematical physics and probability
Yvan Velenik (U Geneva) and F. den Hollander (UL)