- Elias Hedwig (2021): The Picard group of a ring.
The thesis discusses the Picard group of a commutative ring R and its various incarnations: via the Grothendieck group, via Weil divisors or as the class group.
- Nico Wolf (2020): The big Witt ring functor.
The thesis presents the theory of the big Witt ring functor. Lambda rings and their properties are discussed, and then Witt polynomials and Witt vectors are studied. The constructions follows an idea of Lenstra. The link to Symm, the Hopf algebra of symmetric functions, is also explained.
- Jan Thomm (2020): Every abelian group is a class group.
The thesis gives a detailed proof of Claborn's classical theorem that every abelian group arises as the class group of a Dedekind ring. The main strategy is to first realize it as the class group of a Krull domain and then use some approximation argument to get to the Dedekind case.
- Benjamin Görg (2020): Hopf algebras of rooted trees.
This thesis gives an overview about several Hopf algebras built from rooted (planar) trees, in particular the Connes-Kreimer Hopf algebra. After some preparations (e.g. the Milnor-Moore theorem) these Hopf algebras are defined and studied. The thesis concludes with the study of Pre-Lie structures on one of these Hopf algebras.
- Marena Richter (2020): Classification of simple Lie superalgebras.
The thesis revisits and reproves Kac classification of basic classical Lie superalgebras from the 70's. To this end, Lie superalgebras are introduced. The main tool of the classification is a study of the action of the even part (a reductive Lie algebra) on the odd part of the Lie superalgebra.
- Ulukbek Akynbaev (2019): Modular representation theory and the Verlinde category.
The thesis studies properties of the Verlinde category, the semisimplification of the representation category of the cyclic group Z_p over a field of characteristic p. At first the necessary background about monoidal categories and semisimplifications is developed. Among the main statements about Ver_p is a computation of the fusion rules and the conclusion that Ver_p does not admit a (super) fibre functor to vec or svec.