# Archived Events

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## MPI-Oberseminar

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Organiser(s):
C. Kaiser
Date:
Thu, 2013-01-31 15:00 - Thu, 2026-12-31 16:00
Location:
MPIM Lecture Hall

The Oberseminar is a very long running seminar at MPI (‘Ober‘ standing for 'upper'). Its idea is that the guests of the MPI speak in this seminar (hopefully early in their stay) and get the chance to explain their work to the other guests.

## Friedrich Hirzebruch Lecture

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Location:
University Club Bonn

The annual Friedrich Hirzebruch Lecture is a series of lectures started in 2007 on the occasion of the 80th birthday of Prof. Friedrich Hirzebruch. The lectures address a general audience and aim at illustrating the relation between mathematics and art, society and other fields.

## "Pentagramma Mirificum". Hirzebruch lecture by Sergey Fomin on Friday, November 8, University Club Bonn

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Speaker:
Sergey Fomin
Affiliation:
University of Michigan
Date:
Fri, 2019-11-08 18:00 - 19:00
Location:
University Club Bonn

Pentagramma Mirificum (the miraculous pentagram) is a beautiful geometric construction studied by Napier and Gauss. Its algebraic description yields the simplest instance of cluster transformations, a remarkable family of recurrences which arise in diverse mathematical contexts, from representation theory and enumerative combinatorics to theoretical physics and classical geometry (Euclidean, spherical, or hyperbolic).

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Speaker:
Jeanne Scott
Affiliation:
Date:
Tue, 2019-09-24 14:00 - 15:00
Location:
MPIM Lecture Hall

The theory of random Delaunay triangulations of the plane has been proposed by
David-Eynard and others as a discrete model for 2-dimensional quantum gravity: In this model
the role of a continuous metric is played by a Delaunay triangulation while flat metrics
correspond to isoradial triangulations (on which one can define a theory of discrete analyticity).
Like the continuous case, the partition function for this discrete theory is given by a suitably
normalized determinant of a Beltrami-Laplace operator which varies with the choice of

## Workshop on 4-manifolds, September 16 - 20, 2019

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Organiser(s):
David Gay, Jeffrey Meier, Arunima Ray, and Peter Teichner
Date:
Mon, 2019-09-16 10:00 - Fri, 2019-09-20 16:00
Location:
MPIM Lecture Hall

## Workshop on 4-manifolds, September 16 - 20, 2019

#### Organizers

David Gay (University of Georgia/MPIM Bonn)
Jeffrey Meier (University of Georgia)
Arunima Ray (MPIM Bonn)
Peter Teichner (MPIM Bonn)

#### Confirmed Speakers:

Michael Freedman (Station Q & UC Santa Barbara)
David Gabai (Princeton)
Robert Gompf (UT Austin)
Sergei Gukov (Caltech)
András Juhász (Oxford)
Du Pei (Caltech)
Lisa Piccirillo (UT Austin)
Juanita Pinzón-Caicedo (North Carolina State University/MPIM Bonn)
Mark Powell (Durham)
Rob Schneiderman (CUNY)
Hannah Schwartz (Bryn Mawr/MPIM Bonn)
Laura Starkston (UC Davis)
András Stipsicz (Alfred Renyi)
Alex Zupan (University of Nebraska Lincoln)

## tba

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Speaker:
Yingkun Li
Affiliation:
Date:
Wed, 2019-09-04 14:30 - 15:30
Location:
MPIM Lecture Hall
Parent event:
Number theory lunch seminar

## Rational points on quartic del Pezzo surfaces with a conic bundle structure

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Speaker:
Affiliation:
MPIM
Date:
Tue, 2019-09-03 14:00 - 15:00
Location:
MPIM Lecture Hall

There are three possibilities for the quotient of the Brauer group of X modulo constants when X is a del Pezzo surface of degree four over the rational numbers . In this talk we will explain how often each of them occurs when X ranges across a family of quartic del Pezzo surfaces equipped with a conic bundle structure. We will also give an explicit description of the generators of this quotient which allows us to calculate the frequency of such surfaces violating the Hasse principle. This talk is based on a joint work in progress with Cecília Salgado.

## Puzzles about trisections of 4-manifolds

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Speaker:
David Gay
Affiliation:
University of Georgia/MPIM
Date:
Thu, 2019-08-29 15:00 - 16:00
Location:
MPIM Lecture Hall
Parent event:
Colloquium
Parent event:
MPI-Oberseminar

A trisection of a smooth 4-manifold is a very natural kind of decomposition into three elementary pieces which I will describe. Trisections are a natural 4-dimensional analogue of Heegaard splittings of 3-manifolds, a class of decompositions into two pieces that have yielded tremendous insight into 3-dimensional topology, so the philosophy is that trisections should give a way to port 3-dimensional techniques, questions and results to dimension four.

## Chebyshev’s bias for products of k primes and Greg Martin’s conjecture

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Speaker:
Xianchang Meng
Affiliation:
Universität Göttingen/MPIM
Date:
Wed, 2019-08-28 14:30 - 15:30
Location:
MPIM Lecture Hall
Parent event:
Number theory lunch seminar

For any $k\geq 1$, we study the distribution of the difference between the number of integers $n\leq x$ with $\omega(n)=k$  or $\Omega(n)=k$ in two different arithmetic progressions, where $\omega(n)$ is the number of distinct prime factors of $n$ and $\Omega(n)$ is the number of prime factors of $n$ counted with multiplicity . Under some reasonable assumptions, we show that, if $k$ is odd, the integers with $\Omega(n)=k$ have preference for quadratic non-residue classes; and if $k$ is even, such integers have preference for quadratic residue classes.

## An introduction to quantum computing and quantum error correction (with a connection to Howe duality)

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Speaker:
David Gross
Affiliation:
Universität zu Köln
Date:
Tue, 2019-08-27 15:00 - 16:00
Location:
MPIM Lecture Hall

Recently, Gurevitch and Howe have associated a notion of "rank" to representations of the symplectic group, and showed that "highest rank" representations satisfy a form of Howe duality over finite fields (c.f. talk on the 20th). Montealegre-Mora and me then realized that the rank-deficient reps occurring in this context can be characterized in terms of certain quantum error correcting codes. The purpose of this talk is to explain the background of this development, i.e. why physicists care about these objects in the first place.

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