Johan Commelin

I am a postdoc in the group of Stefan Kebekus. My main interest lies in algebraic geometry and algebraic number theory.

From 2017 till 2018 I was a postdoc of Carel Faber in Utrecht (NL). From 2013 till 2017 I was a PhD student in Nijmegen (NL), supervised by Ben Moonen.

Current research topics include: Hodge theory, Galois representations, motives, Mumford–Tate conjecture, periods.

News & Olds

Contact details

@: initials (funny symbol) (initials = jmc)
— PGP keys: [public] [private]
A: Room 425
Albert–Ludwigs-Universität Freiburg
Mathematisches Institut
Ernst-Zermelo-Straße 1
79104 Freiburg im Breisgau


  1. With Annette Huber. Exponential periods and o-minimality II. [arXiv:2007.08290]
  2. With Annette Huber and Philipp Habegger. Exponential periods and o-minimality I. [arXiv:2007.08280]
  3. With Kevin Buzzard and Patrick Massot. Formalising perfectoid spaces Certified Programs and Proofs 2020, 299-312. [offprint] [arXiv:1910.12320] [project webpage]
  4. With Victoria Cantoral Farfán. The Mumford–Tate conjecture implies the algebraic Sato–Tate conjecture of Banaszak and Kedlaya [arXiv:1905.04086]
  5. With Matteo Penegini. On the cohomology of surfaces with pg = q = 2 and maximal Albanese dimension. Trans. Amer. Math. Soc. 373 (2020) 1749-1773. [arXiv:1901.00193]
  6. On compatibility of the ℓ-adic realisations of an abelian motive. Annales de l’Institut Fourier. Volume 69 (2019) no. 5, p. 2089–2120. [link]
  7. The Mumford–Tate conjecture for products of abelian varieties. Algebraic Geometry (6) 6 (2019) 650–677. [link]
  8. The Mumford–Tate Conjecture for the Product of an Abelian Surface and a K3 Surface. Documenta Math. 21 (2016) 1691–1713. [link]

Current and upcoming teaching

Teaching: Coxeter Groups and Lie AlgebrasSummer 2020
Assistent for Introduction to Algebraic CurvesSummer 2020
Assistent for Mathematics for Natural Scientists IISummer 2020
Assistent for Cohomology of Algebraic VarietiesWinter 19/20
Assistent for Mathematics for Natural Scientists IWinter 19/20
Seminar Local FieldsSummer 2019
Linear Algebra 2Summer 2019

Other writing

My PhD thesis: On ℓ-adic compatibility for abelian motives & the Mumford–Tate conjecture for products of K3 surfaces [Erratum]. Completed in the summer of 2017 under the supervision of Ben Moonen.

I wrote my master's thesis, titled Algebraic cycles, Chow motives, and L-functions, in the spring of 2013 under the supervision of Robin de Jong.

I wrote my bachelor's thesis, titled Tannaka Duality for Finite Groups, in the spring of 2011 under the supervision of Lenny Taelman.

Side projects