Maximilian
Siebel
Search by speaker
Filter institution
Filter content
15. January
Today
Alheydis
Geiger
Realizing self-projecting Matroids
Abstract.
Self-dual point configurations have been studied throughout the centuries. In this talk the generalization to self-projecting point configurations will be introduced. These give rise to self-projecting matroids, in other words, to matroids that satisfy the disjoint bases property and that have no almost generic element. The parameter space of self-projecting point configurations is the self-projecting Grassmannian. This is also the space of self-projecting realizations of self-projecting matroids. Its structure is interesting from multiple perspectives, like mathematical physics. We compute the realization spaces for small matroids up to rank 4 on 9 elements. There will be a short overview of the available code and database. If time permits, I will finish with an outlook on the perspective of tropical geometry and subdivisions of matroid polytopes. This project is joint work with Francesca Zaffalon.
Francesca
Primavera
University of California
16. January
Tomorrow
Daan
Janssen
University of York
Boundaries, corners and edge modes: semi-local observables for electromagnetism
Abstract.
For gauge field theories on spacetimes with (asymptotic) boundaries, the gauge transformations acting non-trivially at boundaries and/or corners have a distinguished role compared to those acting purely in the bulk, where the latter are viewed as redundancies, the former play an important role in boundary/infrared features of these theories. We investigate the quantum electromagnetic field on spacetimes with boundaries and corners, and construct algebras of semi-local observables sensitive to the boundary gauge group. We discuss the role of these observables in gluing procedures and superselection theory for electromagnetism, as well as the existence of physically well behaved (Hadamard) states on these algebras.
20. January
Tue W03
Burkhard
Eden
HU Berlin
The off-shell one and two-loop box recovered from intersection theory
Abstract.
We advertise intersection theory for generalised hypergeometric functions as a means of evaluating Mellin-Barnes representations. As an example, we study two-parameter representations of the off-shell one- and two-loop box graphs in exactly four-dimensional configuration space. Closing the integration contours for the MB parameters we transform these into double sums. Polygamma functions in the MB representation of the double box and the occurrence of higher poles are taken into account by parametric differentiation. Summing over any one of the counters results into a <sub>p+1</sub>F<sub>p</sub> that we replace by its Euler integral representation. The process can be repeated a second time and results in a two- or four-parameter Euler integral, respectively. We use intersection theory to derive Pfaffian systems of equations on related sets of master integrals and solve for the box and double box integrals reproducing the known expressions. Finally, we use a trick to re-derive the double box from a two-parameter Euler integral. This second computation requires only very little computing resources.
Falk
Hante
HU Berlin
Stabilizing PDE Control: Optimization and Feedback in Moving Horizons
21. January
Wed W03
Ulrike
Schneider
Universität Wien
A Unified Framework for Pattern Recovery in Penalized Estimation
Abstract.
We consider the framework of least-squares penalized estimation where the penalty term is given by a polyhedral norm, or more generally, a polyhedral gauge, which encompasses methods such as LASSO and generalized LASSO, SLOPE, OSCAR, PACS and others. Each of these estimators can uncover a different structure or pattern of the unknown parameter vector. We define a novel and general notion of patterns based on subdifferentials and formalize an approach to measure pattern complexity. For pattern recovery, we provide a minimal condition for a particular pattern to be detected with positive probability, the so-called accessibility condition. We make the connection to estimation uniqueness by showing that uniqueness holds if and only if no pattern with complexity exceeding the rank of the X-matrix is accessible. Subsequently, we introduce the noiseless recovery condition which is a stronger requirement than accessibility and which can be shown to play exactly the same role as the well-known irrepresentability condition for the LASSO – in that the probability of pattern recovery is bounded by 1/2 if the condition is not satisfied. Through this, we unify and extend the irrepresentability condition to a broad class of penalized estimators using an interpretable criterion. We also look at the gap between accessibility and the noiseless recovery condition and discuss that our criteria show that it is more pronounced for simple patterns. Finally, we prove that the noiseless recovery condition can indeed be relaxed when turning to so-called thresholded penalized estimation: in this setting, the accessibility condition is already sufficient (and necessary) for sure pattern recovery provided that the signal of the pattern is large enough. We demonstrate how our findings can be interpreted through a geometrical lens throughout the talk and illustrate our results for the Lasso as well as other estimation procedures.
Yannic
Steenbeck
TU Braunschweig
Olaf
Klein
WIAS
Uncertainty quantification for a model for a magnetostrictive material involving a hysteresis operator
Abstract
Jan Moritz
Petschick
Uni Bielefeld
Maximal subgroups in branch groups
Abstract.
Branch groups are groups whose subgroup structure resembles a rooted tree. Among many other intriguing properties, they contain examples of groups with unusual restrictions on their maximal subgroups. In this talk, I will provide an account of what is known about maximal subgroups of branch groups and present some recent results.
22. January
Thu W03
Bernhard
Eisvogel
On slow-fast systems
Karl
Worthmann
Karan
Mukhi
Raphael
Kuess
HU Berlin
23. January
Fri W03
Malte
Leimbach
MPI Bonn
Spectral truncations and operator systems in noncommutative geometry
Abstract.
Spectral truncations are compressions of spectral triples by spectral projections for the Dirac operator. This formalism was introduced by Connes--van Suijlekom to reflect constraints on the availability of spectral data, and they advocate for considering operator systems rather than C*-algebras in noncommutative geometry. Connecting to the setting of Rieffel's compact quantum metric spaces and Kerr--Li's operator Gromov--Hausdorff distance, it makes sense to ask about convergence of spectral truncations. I will report on recent progress on this question for tori and compact quantum groups.
Janina
Bernardy
MPI Bonn
27. January
Tue W04
Maciej
Dolega
Institute of Mathematics, Polish Academy of Sciences
Nathan
Arnaud
HU Berlin
28. January
Wed W04
Jakob
Runge
Universität Potsdam
Anastasija
Pešić
WIAS
Curvature-driven pattern formation in biomembranes: A gradient flow approach
Rüdiger
Frey
WU Vienna
Andrew
Allen
U Durham
Christopher
Voll
Bielefeld University
Hall-Littlewood polynomials, affine Schubert series, and lattice enumeration
Abstract.
In this talk, I would like you to meet Hall-Littlewood-Schubert series, a new class of multivariate generating functions. Their definition features semistandard Young tableaux and polynomials resembling the classical Hall-Littlewood polynomials. Their intrinsic beauty notwithstanding, Hall-Littlewood-Schubert series have many applications to counting problems in algebra, geometry, and number theory. In my talk the spotlight will be on applications to affine Schubert series. These may be seen as an integral analogue of the Poincare polynomials enumerating the rational points over finite fields of classical Schubert varieties. The latter parametrize subspaces of a given vector space by the intersection dimensions with a fixed flag of reference. This work is joint with Joshua Maglione. I will explain things from scratch, assuming no familiarity with the advanced technical vocabulary used in this abstract.
29. January
Thu W04
Ran
Tao
MPI MiS Leipzig
János
Nitschke
HU Berlin
Ben
Smith
Xiaofei
Sei
University of Toronto
Claudio
Dappiaggi
University of Pavia
Equivalence between local and global Hadamard States with Robin boundary conditions on half-Minkowski spacetime
Abstract.
We construct the fundamental solutions and Hadamard states for a Klein-Gordon field in half-Minkowski spacetime with Robin boundary conditions in arbitrary dimensions using a generalisation of the Robin-to-Dirichlet map. On the one hand this allows us to prove the uniqueness and support properties of the Green operators. On the other hand, we obtain a local representation for the Hadamard parametrix that provides the correct local definition of Hadamard states, capturing `reflected' singularities from the spacetime timelike boundary. This allows us to prove the equivalence of our local Hadamard condition and the global Hadamard condition with a wave-front set described in terms of generalized broken bicharacteristics, obtaining a Radzikowski-like theorem in half-Minkowski spacetime. Joint work with B. Costeri, R. D. Singh and B. Juárez-Aubry -- ArXiv: 2509.26035 [math-ph]
Alessandro
Bondi
École Polytechnique Paris
30. January
Fri W04
Beatrice
Costeri
University of Pavia
03. February
Tue W05
Gaëtan
Borot
HU Berlin
Panorama of matrix models and topological recursion IV
Abstract.
This is crash course which aims at explaning various aspects of: random matrix ensembles and Coulomb gases, loop equations, spectral curves, topological recursion, maps, free probability, how they fit together and pose some open problems.
04. February
Wed W05
Frank
Konietschke
Charité
05. February
Thu W05
Ran
Tao
MPI MiS Leipzig
János
Nitschke
HU Berlin
10. February
Tue W06
Andrea
Brini
Sheffield University
On the conifold gap for the local projective plane
Abstract.
The conifold gap conjecture asserts that the polar part of the Gromov-Witten potential of a Calabi-Yau threefold near its conifold locus has a universal expression described by the logarithm of the Barnes G-function. In this talk I will describe a proof of the conifold gap conjecture for the local projective plane, whereby the higher genus conifold Gromov-Witten generating series of local P<sup>2</sup> are related to the thermodynamics of a certain statistical mechanical ensemble of repulsive particles on the positive half-line. As a corollary, this establishes the all-genus mirror principle for local P<sup>2</sup> through the direct integration of the BCOV holomorphic anomaly equations.
11. February
Wed W06
Ho
Yun
EPFL
Linear Monge is All You Need
Abstract.
In this talk, we explore the geometry of the Bures-Wasserstein space for potentially degenerate Gaussian measures on a separable Hilbert space, based on our recent work with Yoav Zemel. A key feature of our approach is its simplicity: relying only on elementary arguments from linear operator theory, we are able to derive explicit results without resorting to Kantorovich duality or Otto's Calculus. We provide a complete characterisation of both the Monge and Kantorovich problems in this context, regardless of the degeneracy of their measures. Furthermore, we show a simple way to construct all possible Wasserstein geodesics connecting two Gaussian measures. Finally, we generalise our results to characterise Wasserstein barycenters of Gaussian measures, borrowing the idea of Procrustes distance from statistical shape analysis.
Béatrice
Matteo
University of Geneva
Kernel ridge regression for spherical responses
Abstract.
The aim is to propose a novel nonlinear regression framework for responses taking values on a hypersphere. Rather than performing tangent space regression, where all the sphere responses are lifted to a single tangent space on which the regression is performed, we estimate conditional Fréchet means by minimizing squared distances on the nonlinear manifold. Yet, the tangent space serves as a linear predictor space where the regression function takes values. The framework integrates Riemannian geometry techniques with functional data analysis by modelling the regression function using methods from vector-valued reproducing kernel Hilbert space theory. This formulation enables the reduction of the infinite-dimensional estimation problem to a finite-dimensional one via a representer theorem and leads to an estimation algorithm by means of Riemannian gradient descent. Explicit checkable conditions on the data that ensure the existence and uniqueness of the minimizing estimator are given.
Elias
Zimmermann
Universität Leipzig
Andrea
Poiatti
Universität Wien
A Navier--Stokes/Mullins--Sekerka system with different densities: weak solutions
Abstract
Tony
Lelievre
CERMICS
Vitalii
Konarovskyi
U Hamburg
12. February
Thu W06
Alexander
Schill
Andre
Zepernick
Rudi
Pendavingh
Guido
Gazzani
University of Verona
Beatrice
Ongarato
Technische Universität Dresden
14. February
Sat W06
Mikhail
Gorsky
Jean Monnet University
04. March
Wed W09
Felix
Röhrle
University of Tübingen
15. April
Wed W15
Pierluigi
Colli
Università Pavia, Italy
16. April
Thu W15
José Antonio
Carrillo
University of Oxford, United Kingdom
21. April
Tue W16
Pierrick
Bousseau
Oxford University
05. May
Tue W18
Damien
Simon
Sorbonne Universite
20. May
Wed W20
Riccarda
Rossi
University of Brescia, Italy
14. July
Tue W28
Alexander
Alexandrov
IBS Pohang
17. December
Thu W50
Lars
Kastner
TU Berlin
Drawing algebraic curves in OSCAR