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## MPI-Oberseminar

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

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.

## Introduction to the Farrell-Jones Conjecture

We explain the Farrell-Jones Conjecture for the algebraic K-groups and L-groups of group rings of torsion free groups. It relates them to the homology of the classifying space BG. There is also a more advanced version for arbitrary groups, the Full Farrell-Jones Conjecture and we will explain its status. Actually, it is known to be true for a rather large class of groups including hyperbolic groups, CAT(0)-groups, lattices in almost connected Lie groups and fundamental groups of 3-manifolds.

## tba

https://hu-berlin.zoom.us/j/61339297016

## tba

https://hu-berlin.zoom.us/j/61339297016

## Fukaya category of surfaces and pants decomposition

In this talk I will explain some results joint with James Pascaleff on the Fukaya category of Riemann surfaces. I will explain a local-to-global principle which allows us to reduce the calculation of the Fukaya category of surfaces of genus g greater than one to the case of the pair-of-pants, and which holds both in the punctured and in the compact case. The starting point are the sheaf-theoretic methods which are available in the exact setting, and which I will review at the beginning of the talk.

## Lecture course "From 3-manifold invariants to number theory"

https://zoom.us/j/96952516566?pwd=Z3NyZW04M2YxSHo2MWdlOHJ4MlNpUT09

Meeting ID: 969 5251 6566

Passcode: 307018

## Topological rigidity and Positive scalar curvature

`The topological structure of contractible 3-manifolds is much complicated. For example, the Whitehead manifold is a contractible 3-manifold but not homeomorphic to $\mathbf{R}`

3$. In the talk, we will use minimal surfaces theory to present a proof that the Whitehead manifold has no complete metric with positive scalar curvature.## Hypercovers, Sheafification, and Applications

In this talk we begin by reviewing the usual sheafification construction for presheaves of sets, and observe already how hypercovers come into play. We will try and highlight which properties are used from the structure of a Grothendieck topology along the way. Next, having set this familiar construction up in a way that generalizes to simplicial presheaves, we describe the "plus construction" as a colimit over all hypercovers and discuss what it would take to show that this results in a simplicial sheaf in the local projective model structure.

## Differential cohomology theories are sheaves on manifolds

location: https://zoom.us/j/99428054844?pwd=NXlRVmJobUhFZTFtQUQrZ29RZk81dz09

Meeting-ID: 994 2805 4844

For passcode contact Christian Kaiser (kaiser@mpim...).

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