Universität Bonn

Events Calendar

May 2024

Location: MPIM Lecture Hall

Link

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

Location: MPIM Lecture Hall

Location: SemR N0.003, Endenicher Allee 60

Abstract:
The elementary theory of the differential field of (logarithmic-exponential) transseries has been completely axiomatized by Aschenbrenner--van den Dries--van der Hoeven, and this theory is model complete. This talk concerns pairs of models of this theory such that one is a tame substructure of the other. Tameness here is meant in the sense of a tame pair of real closed fields, which goes back to van den Dries--Lewenberg and, ultimately, Macintyre and Cherlin--Dickmann. I will describe work in progress on the model theory of such transserial tame pairs, including a model completeness result for them. An example comes from the differential field of hyperseries, constructed by Bagayoko--Kaplan--van der Hoeven and shown to be an elementary extension of the differential field of transseries by Bagayoko, equipped with an exponentially bounded subfield.

Location: Seminarraum, 1st floor

Abstract: We study the d-dimensional Vector Bin Packing (dVBP) problem, a generalization of Bin Packing with central applications in resource allocation and scheduling. In dVBP, we are given a set of items, each of which is characterized by a d-dimensional volume vector; the objective is to partition the items into a minimum number of subsets (bins), such that the total volume of items in each subset is at most 1 in each dimension. Our main result is an asymptotic approximation algorithm for dVBP that yields a ratio of (1 + ln d − χ(d) + ε) for all d ∈ N and any ε > 0; here, χ(d) is some strictly positive function. This improves upon the best knownasymptotic ratio of (1 + ln d + ε) due to Bansal, Caprara and Sviridenko (SICOMP 2010) for
any d > 3. By slightly modifying our algorithm to include an initial matching phase andapplying a tighter analysis, we obtain an asymptotic approximation ratio of (4/3 + ε) for the
special case of d = 2, thus substantially improving the previous best ratio of (3/2 + ε) due to Bansal, Eliáš and Khan (SODA 2016). Our algorithm iteratively solves a configuration LP relaxation for the residual instance (from previous iterations) and samples a small number of configurations based on the solution for the configuration LP. While iterative rounding was
already used by Karmarkar and Karp (FOCS 1982) to establish their celebrated result for classic (one-dimensional) Bin Packing, iterative randomized rounding is used here for the first
time in the context of Vector Bin Packing. Our results show that iterative randomized rounding is a powerful tool for approximating dVBP, leading to simple algorithms with improved approximation guarantees.

Location: MPIM Seminar Room 

Location: MPIM Seminar Room 

Location: Endenicher Allee 60, seminar room 0.008

Abstract:
I will briefly introduce noncommutative geometry and one of its main technical devices, unbounded KK-theory, and then discuss how dynamical systems can be represented therein. One important concept for this purpose is equivariant KK-theory. In the development of unbounded KK-theory, an aspect which has been left unresolved is the definition of equivariance. One reason for this is that the natural definition fails to capture all the degrees of freedom available in the usual, bounded equivariant KK-theory. This is apparent already in the commutative case, as we shall see. In light of the forgoing, conformal geometry will be briefly introduced and I will discuss the definition of conformally equivariant unbounded KK-theory. I also will touch on ongoing work which uses these tools to analyse group actions on parabolic geometries and more general dynamical systems.

Location: Seminarraum MPI

Abstract:
For any finite k-group scheme G acting rationally on a k-variety X, if the action is generically free then the dimension of Lie (G) is upper bounded by the dimension of the variety.This inequality turns out to be also a sufficient condition for the existence of such actions, when k is a perfect field of positive characteristic and G is infinitesimal commutative trigonalizable. These group schemes are non-reduced and arise only in positive characteristic. After presenting the main objects involved and overviewing the motivation for this problem, we will explain the result in the case of actions of the p-torsion of a supersingular elliptic curve.

Location: MPIM Lecture Hall 

Location: Endenicher Allee 60, Lipschitz hall

Website

Location: MPIM Seminar Room 

Location: Raum 1.008

Abstract: In this talk I will discuss how to generalize the axioms of braided monoidal structure, and more generally En algebras, for higher categories. In particular, by repeated use of the Eckmann-Hilton argument, we will derive a ''minimal'' set of axioms for braided monoidal structures for general higher categories. No knowledge on higher categories and homotopy theory will be assumed.

Location: MPIM Lecture Hall

Location: MPIM Seminar Room

Location: Endenicher Allee 60, Raum 0.011 

Abstract:
This will be a survey style talk. I will discuss the spaces of traces and characters on a countable group and their relations with the spaces of normal subgroups, invariant random subgroups and other related structures. I will give some examples and then specialize at arithmetic groups, explain the state of the art and discuss some conjectures.

Location: MPIM Lecture Hall

Location: MPIM Lecture Hall

Location: Endenicher Allee 60, Lipschitz Saal 

Abstract:

In this talk, I will present recent process on a joint work with Jani Lukkarinen. We study the time-evolution of cumulants the kinetic energies in Kac's stochastic model for velocity exchange of N particles. Our aim is to quantify how fast – on a time scale in which the collision rate for each particle is of order one – these degrees of freedom become chaotic. Chaos here is understood in the sense of almost complete independence of the relevant dynamical random variables (kinetic energies of the particles) which we measure by the magnitude of their cumulants up to a finite, but arbitrary order.

Known spectral gap results imply that typical initial densities converge to uniform distribution on the constant energy sphere at (rescaled) times comparable to N, and the more recent entropy production arguments give similar time orders. We prove that the finite order cumulants converge to their small stationary values ​​much faster, already at (rescaled) times of order (i) one or (ii) log(N), depending on the magnitude of the initial non-independence of the kinetic energy. The proof relies on stability analysis of the closed, but nonlinear, hierarchy of energy cumulants around the fixed point formed by their values ​​in the stationary spherical distribution.

Location: MPIM Lecture Hall

Location: Endenicher Allee 60, Seminar Room 1.008

Abstract:

This talk is based on a joint work in progress with Gurbir Dhillon. A remarkable theorem of Feigin and E. Frenkel from the early 90's describes the center of the universal enveloping algebra of an (untwisted) affine Kac-Moody Lie algebra at the so-called critical level proving a conjecture of Drinfeld: the center in question is the algebra of polynomial functions on an infinite dimensional affine space known as the space of operas. In our work we study a part of the center in positive characteristic p at an arbitrary non-critical level. Namely, we prove that the loop group invariants in the completed universal enveloping algebra is still the algebra of polynomials on an infinite dimensional affine space that is ``p times smaller than the Feigin-Frenkel center''. In my talk I will introduceall necessary notions, state the result, explain motivations and examples.   

Location: MPIM Lecture Hall

Location: MPIM Seminar Room

Location: MPIM Lecture Hall

Location: MPIM Lecture Hall

Location: MPIM Lecture Hall

Location: Endenicher Allee 60, Lipschitz hall

Link

Location: MPIM Lecture Hall

Location: MPIM Lecture Hall

Location: MPIM Lecture Hall

Location: Endenicher Allee 60, seminar room 0.008

Abstract: TBA

Location: MPIM Lecture Hall

Location: *N0.008* (Endenicher Allee 60)

Abstract: A group is called profinitely rigid if it can be recognized only by looking at its finite quotients. It is still an open question whether $SL(n,\mathbb{Z})$ is profinitely rigid. While the full answer to this question is still unknown, I will construct finite index subgroups of $SL(n,\mathbb{Z})$ which are not profinitely rigid (at least when $n>2$). These constructions can be generalized to show that a "typical" arithmetic group exhibits non-isomorphic finite index subgroups whose profinite completions are isomorphic. If time permits I will explain why this can not happen in the exceptional cases.

Location: Endenicher Allee 60, Lipschitz hall

Link

Location: Endenicher Allee 60, SR.0.007

Abstract: Algebraic Montgomery-Yang problem predicts that a normal projective surface with quotient singularities has at most 4 singular points if its second Betti number is 1. This is an algebraic version of the original Montgomery-Yang problem concerning the number of exceptional orbits of pseudo-free circle actions on the five dimensional sphere. The algebraic Montgomery-Yang problem remains open when the surface is rational and the canonical divisor is ample.

In this talk, we will briefly review the history of the problem and explain known results both in algebraic version and in the recent smooth version by Woohyeok Jo, Jongil Park,and Kyungbae Park. We conclude the discussion by proposing a conjecture, called the cascade conjecture, which implies the algebraic Montgomery-Yang problem.

June 2024

Invited Speakers:

  • Mirela Ben-Chen (Technion Israel Institute of Technology)
  • Sergio Conti (University of Bonn)
  • Patrick Dondl (Albert-Ludwigs-Universität Freiburg)
  • Martin Metscher (MTU Aero Engines AG)
  • Felix Otto (Max-Planck-Institut für Naturwissenschaften)
  • Tobias Preußer (Fraunhofer Institute for Digital Medicine MEVIS)
  • Carola-Bibiane Schönlieb (University of Cambridge)
  • Peter Schröder (California Institute of Technology)
  • Rüdiger Schultz (Universität Duisburg-Essen)
  • Gabriele Steidl (Technische Universität Berlin)
  • Robert Strzodka (Universität Heidelberg)
  • Max Wardetzky (Universität Göttingen)
  • Barbara Zwicknagl (Humboldt-Universität zu Berlin)

Location: Lipschitz hall, Endenicher Allee 60, 53115 Bonn

Link

Location: Endenicher Allee 60, Raum 0.008 

Abstract:
TBA

Location: Endenicher Allee 60, Lipschitz hall

Link

Location: Endenicher Allee 60, Lipschitz hall

Abstract:
Fortschritte in der Mathematik beginnen nicht selten damit, dass man etwas Alltägliches, an dem man sonst achtlos vorübergeht, einmal genauer untersucht. Auch hinter einfachen, elementaren Fragen versteckt sich nicht selten schöne und zuweilen anspruchsvolle Mathematik. Davon ausgehend begeben wir uns auf einen Streifzug durch einige kurzweilige Themen der Mathematik.

Link

Location: Endenicher Allee 60, Raum 0.008

Abstract:
In this talk, Jan Uerz will give the final presentation on the topic of his Master's thesis.

Location: Endenicher Allee 60, Lipschitz hall

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Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

Location: Endenicher Allee 60, Raum 0.008

Abstract:
In diesem Vortrag wird Juri Langer das Thema seiner Bachelorarbeit vorstellen.
(This talk will be in German.)

Location: Endenicher Allee 60, Raum 0.008

Abstract:
In this talk, André de Sousa Guimarães will introduce the topic of his Master's thesis.

Location: Endenicher Allee 60, Lipschitz hall

Link

July 2024

Invited Speakers:

  • Jon Brundan (University of Oregon)
  • Shun-Jen Cheng (Academia Sinica)
  • Kevin Coulembier (University of Sydney)
  • Maria Gorelik (Weizmann Institute)
  • Victor Kac (MIT)
  • Jonathan Kujawa (University of Oklahoma)
  • Andrew Manion (NC State University)
  • Jonas Nehme (University of Bonn)
  • Shifra Reif (Bar-Ilan University)
  • Lev Rozansky (University of Chapel-Hill)
  • Siddharta Sahi (Rutgers University)
  • Hadi Salmasian (University of Ottawa)
  • Vera Serganova (University of California, Berkeley)
  • Alexander Sherman (University of Sydney)

Location: Lipschitz hall, Endenicher Allee 60, 53115 Bonn

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Location: Endenicher Allee 60, Lipschitz hall

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Location: Lennéstr. 2, Seminarraum

Link (incl. Abstract)

Invited Speakers:

  • Michael Christ (UC Berkeley)
  • Philip Gressman (U. Penn)
  • Ian Petrow (UCL)
  • James Wright (U. Edinburgh)
  • Ruixiang Zhang (UC Berkeley)
  • Polona Durcik (Chapman University)
  • Dóminique Kemp (UW Madison/IAS/Princeton)
  • Dominique Maldague (MIT)
  • Hong Wang (UCLA)

Location: Lipschitz hall, Endenicher Allee 60, 53115 Bonn

Link

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

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Location: Endenicher Allee 60, Lipschitz hall

Link

Invited Speakers:

  • Jonathan Bennett (University of Birmingham)
  • Xiumin Du (Northwestern University)
  • Malabika Pramanik (UBC)
  • Andreas Seeger (UW Madison)

Location: Lipschitz hall, Endenicher Allee 60, 53115 Bonn

Link

Location: Endenicher Allee 60, Lipschitz hall

Link

Location: MPIM Lecture Hall

Link

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

August 2024

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

September 2024

Location: MPIM Lecture Hall 

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Invited Speakers:

•    Alice Guionnet (Ecole Normale Supérieure Lyon)
•    Ioan Manolescu (University of Fribourg)
•    
Eliran Subag (Weizmann Institute of Science, Israel)
•    
Simone Warzel (Technical University of Munich)

Location: Lipschitz hall, Endenicher Allee 60, 53115 Bonn

Link

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

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Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

Invited Speakers:

  • Adolfo Arroyo-Rabasa (Catholic University of Louvain)
  • Annika Bach (Eindhoven University of Technology)
  • Giulia Bevilacqua (University of Pisa)
  • Elise Bonhomme (Free University of Brussels)
  • Camilla Brizzi (Technical University of Munich)
  • Elia Brué (Bocconi University, Milan)
  • Leon Bungert (University of Würzburg)
  • Sara Daneri (University of L’Aquila)
  • Cristiana De Filippis (University of Parma)
  • Annette Dumas (University Claude Bernard, Lyon )
  • Katharina Eichinger (Polytechnic School, Paris)
  • Xavier Fernandez-Real (EPFL - Swiss Federal Institute of Technology, Lausanne)
  • André Guerra (Institute for Theoretical Studies, ETH, Zurich)
  • Jasper Hoeksema (Eindhoven University of Technology)
  • Domenico Angelo La Manna (University of Naples, Federico II)
  • Tim Laux (University of Regensburg)
  • Alice Marveggio (HCM, Bonn)
  • Roberta Marziani (University of L’Aquila)
  • Mircea Petrache (Catholic Chile Univesity, Santiago)
  • Simone Rademacher (Ludwig Maximilian University of Munich)
  • Sebastian Schwarzacher (Charles University, Prague)
  • Bozhidar Velichkov (University of Pisa)

Location: Endenicher Allee 60, Lipschitz hall

Link

Location: Lecture Hall (Room 0.109), b-it building, Friedrich-Hirzebruch-Allee 6

Website

October 2024

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

November 2024

Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

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Location: HIM lecture hall (Poppelsdorfer Allee 45, Bonn)

Link

December 2024

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