Tue, 15 Nov 2016

14:15 - 15:15
L4

### Representations of finite groups over self-injective rings

Greg Stevenson
(Bielefeld)
Abstract

For a group algebra over a self-injective ring
there are two stable categories: the usual one modulo projectives
and a relative one where one works modulo representations
which are free over the coefficient ring.
I'll describe the connection between these two stable categories,
which are "birational" in an appropriate sense.
I'll then make some comments on the specific case
where the coefficient ring is Z/nZ and give a more
precise description of the relative stable category.

Tue, 24 May 2016

14:15 - 15:15
L4

### Thurston and Alexander norms, and the Bieri-Neumann-Strebel invariants for free-by-cyclic groups

Dawid Kielak
(Bielefeld)
Abstract

We will introduce the Thurston norm in the setting of 3-manifold groups, and show how the techniques coming from L2-homology allow us to extend its definition to the setting of free-by-cyclic groups.
We will also look at the relationship between this Thurston norm and the Alexander norm, and the BNS invariants, in particular focusing on the case of ascending HNN extensions of the 2-generated free group.

Thu, 12 Nov 2015

14:00 - 15:00
L4

### The monoidal structure on strict polynomial functors and adjoints of the Schur functor

Rebecca Reischuk
(Bielefeld)
Abstract

Firstly, we will discuss how the category of strict polynomial functors can be endowed with a monoidal structure, including concrete calculations. It is well-known that the above category is equivalent to the category of modules over the Schur algebra. The so-called Schur functor in turn relates the category of modules over the Schur algebra to the category of representations of the symmetric group which posseses a monoidal structure given by the Kronecker product. We show that the Schur functor is monoidal with respect to these structures.
Finally, we consider the right and left adjoints of the Schur functor. We explain how these can be expressed in terms of one another using Kuhn duality and the central role the monoidal structure on strict polynomial functors plays in this context.

Tue, 13 Oct 2015

14:15 - 15:15
L4

### CANCELLED!

Stefan Witzel
(Bielefeld)
Abstract

If $R = F_q[t]$ is the polynomial ring over a finite field
then the group $SL_2(R)$ is not finitely generated. The group $SL_3(R)$ is
finitely generated but not finitely presented, while $SL_4(R)$ is
finitely presented. These examples are facets of a larger picture that
I will talk about.

Sat, 04 Mar 2006
10:45
L2

Prof B Fischer
(Bielefeld)
Fri, 03 Mar 2006
15:45
L2

C M Ringel
(Bielefeld)
Tue, 07 Mar 2006
17:00
L1

### (3,4) - transpositions, II

Professor Bernd Fischer
(Bielefeld)
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