On 20 April 2026, Prof. Dr Jürgen Klüners, Dean of the Faculty of Computer Science, Electrical Engineering and Mathematics, welcomed junior professor Dr Janina Letz and professor Dr Stephan Stadler to their inaugural lecture. After the dean presented the academic careers of the newly appointed professors, both lectures offered insights into current research issues.
Junior professor Dr Janina Letz started with her lecture "What is the size of a derived category?" and built a bridge between classical rings and modern categories. She explained how commutative rings are analysed through their effect on complexes and how the resulting "derived category" can be measured as a Mathematics object. In particular, she focussed on the question of how the category contains information about the original ring.
This research approach reflects Letz's consistent academic specialisation. After completing her bachelor's degree in Mainz, she moved to the USA, where she completed her doctorate at the University of Utah in Salt Lake City. Her doctoral dissertation on "Generation Time in Derived Categories" (2020) laid the foundation for her current work on tensor-triangulated categories and Hochschild cohomology. Before her call to Paderborn University, she gained extensive experience as a postdoctoral researcher at Bielefeld University and as a Feodor Lynen Fellow of the Alexander von Humboldt Foundation at the University of California, Los Angeles (UCLA).
Professor Dr Stephan Stadler then spoke on the topic of "Not a Knot". He demonstrated how methods of differential geometry can be used to solve topological problems. The Fáry-Milnor theorem was central to this: it states that a knot whose total curvature falls below a certain value must inevitably be an "unknot" (a simple circle). Stadler showed how these concepts are now extended to the geometry of singular spaces and areas with non-positive curvature.
Stadler's scientific career has been characterised by excellent research at leading institutes. He completed his studies and doctorate at LMU Munich, where he worked on obstructions for smooth non-positively curved metrics. After a period as an Academic Counsellor in Munich, he became head of a research group at the Max Planck Institute for Mathematics in Bonn from 2020 to 2025. His expertise in quasi-isometric rigidity and minimal surfaces now strengthens the geometric profile of Mathematics in Paderborn.
The Faculty of Computer Science, Electrical Engineering and Mathematics is delighted to have gained two such high-profile personalities for the site, who will further strengthen the Institute's international network.
