Johann Stumpenhusen Mathematics Institute University of Cologne Weyertal 86-90 50931 Cologne Germany

Office: Room -104 (basement) Telephone: +49 221 470 5429 Office hours: Tuesday 3 - 4 p.m. (during the semester) E-mail: jstumpen (at) math (dot) uni-koeln (dot) de

Since June 2022, I am part of Prof. Dr. Sander Zwegers's working group as his PhD student after finishing my master's in Göttingen under the supervision of Dr. Victoria Cantoral Farfán. My main research interests are arithmetic algebraic number theory and modular forms, especially theta series and locally harmonic Maass forms.

Teaching

Winter 2024/25: Lineare Algebra I (Prof. Dr. Sander Zwegers), teaching assistant.

Summer 2024: Elliptische Kurven (Dr. Johann Franke), teaching assistant.

Summer 2024: Modulformen (Prof. Dr. Sander Zwegers), teaching assistant. [Punkteübersicht Übungen.]

Winter 2023/24: Elliptische Funktionen (Prof. Dr. Sander Zwegers), teaching assistant. [Punkteübersicht Übungen.]

Summer 2023: Elementare Zahlentheorie (Prof. Dr. Sander Zwegers), teaching assistant.

Winter 2022/23: Algebra (Prof. Dr. Sander Zwegers), teaching assistant.

Summer 2022: Lineare Algebra II (Prof. Dr. Sander Zwegers), teaching assistant.

Winter 2019/20 - Winter 2021/22: student assistant for several modules in mathematics at the Georg-August-Universität in Göttingen, including Introduction to Algebraic Number Theory (Dr. Victoria Cantoral Farfán).

Co-supervising

Winter 2024/25: Seminar "Elliptische Funktionen" (with Prof. Dr. Sander Zwegers), co-supervisor

Summer 2024: Seminar "Thetafunktionen" (with Prof. Dr. Sander Zwegers), co-supervisor.

Winter 2023/24: Seminar "Kryptologie" (with Prof. Dr. Sander Zwegers), co-supervisor.

Summer 2023: Seminar "Arithmetische Funktionen" (with Prof. Dr. Sander Zwegers), co-supervisor.

Winter 2022/23: Seminar "Spezielle Funktionen" (with Prof. Dr. Sander Zwegers), co-supervisor.

Conferences, Workshops and Research Visits

ABKLS Seminar, September 2024, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen.

36th Automorphic Forms Workshop, May 2024, Oklahoma State University, Stillwater.

International Conference on L-Functions and Automorphic Forms, May 2024, Vanderbilt University, Nashville.

International conference on modular forms and q-series, March 2024, Universität zu Köln, Cologne.

Conference for Young Number Theorists, September 2023, Max-Planck-Institut für Mathematik, Bonn.

ENTR workshop, October 2022, Technische Universität Darmstadt, Darmstadt.

ABKLS Seminar, September 2022, Universität zu Köln, Cologne.

Modular forms in number theory and beyond, August 2022, Universität Bielefeld, Bielefeld.

ABKLS Seminar, June 2022, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn.

Papers, Preprints and Theses

Preprints

On the Proportion of Coprime Fractions in Number Fields (with Walter Bridges and Johann Franke), 2023, submitted.

Perfect Eisenstein Integers, 2022.

Notes

On the solutions of φ (dn) = φ (d(n+h)), 2023.

Theses

Perfect numbers in the Eisenstein integers and sums of integral squares in quadratic extensions (Master's Thesis), 2022.

Lösungen der Gleichungen φ (n) = φ (n + h) und σ (n) = σ (n + h) sowie deren Übertrag auf algebraische Ganzheitsringe (Bachelor's Thesis, German), 2021.

Talks

Real Analytic Modular Forms, October 2022, Darmstadt.