Ulrik Bo Rufus Enstad

I am a researcher at the University of Oslo leading a three-year researcher project with international mobility funded by the Research Council of Norway. Before returning to the University of Oslo I was a visiting researcher at Stockholm University (August 2021 – March 2023) and the University of Potsdam (April 2023 – June 2023).

I obtained my PhD from the University of Oslo in 2020. My supervisor was Professor Nadia Larsen and my co-supervisor was Professor Franz Luef.

Upcoming

• May 6–8: Point sets: Dynamics, sampling and operator algebras, workshop at the University of Oslo.

• May 13–16: Visit from Eduard Vilalta, Chalmers University of Technology and Gothenburg University. 

• June 17–20: Noncommutativity in the North (MikaelFest), symposium at Chalmers University of Technology and Gothenburg University.

• September 12–13: Nasjonalt matematikermøte 2024, Oslo.

• October 28 - November 1: Noncommutativity behind the dunes, TU Delft, Netherlands.

Research interests

My research interests are in operator algebras and harmonic analysis. Currently I am interested in sampling problems originating in harmonic analysis and how they can be approached using C*-algebras and von Neumann algebras of associated groups and groupoids.

Teaching

• Fall 2024: MAT1120 Linear algebra
• Spring 2021: MAT4450 Advanced Functional analysis
• Spring 2020: MAT3400/MAT4400 Linear analysis with applications (Exercise sessions)
• Autumn 2019: MAT1100 Calculus
• Spring 2019: MAT3400/MAT4400 Linear analysis with applications (Exercise sessions)
• Autumn 2017: MAT3400/MAT4400 Linear analysis with applications (Plenary sessions)
• Spring 2017: MAT2200 Groups, rings and fields (Plenary sessions)
• Autumn 2016: MAT3400/MAT4400 Linear analysis with applications (Plenary sessions)

Articles

1. Free actions of polynomial growth Lie groups and classifiable C*-algebras (with Gabriel Favre and Sven Raum). (2023) preprint. [arxiv]

2. Linear independence of coherent systems associated to lattices (with Jordy Timo van Velthoven). (2023) preprint. [arxiv]

3. A dynamical approach to sampling and interpolation in unimodular groups (with Sven Raum). (2022) preprint. [arxiv]

4. Coherent systems over approximate lattices in amenable groups (with Jordy Timo van Velthoven). Annales de l'Institut Fourier (to appear) (2022) [arxiv]

5. Deformations and Balian-Low theorems for Gabor frames on the adeles (with Mads S. Jakobsen, Franz Luef and Tron Omland). Advances in Mathematics 410, Part B (2022). DOI: 10.1016/j.aim.2022.108771 [arxiv]

6. Smooth lattice orbits of nilpotent groups and strict comparison of projections (with Erik Bédos and Jordy Timo van Velthoven). Journal of Functional Analysis 283, no. 6 (2022). DOI: 10.1016/j.jfa.2022.109572 [arxiv]

7. On sufficient density conditions for lattice orbits of relative discrete series (with Jordy Timo van Velthoven). Archiv der Mathematik. (2022). DOI: 10.1007/s00013-022-01748-8 [arxiv]

8. The density theorem for projective representations via twisted group von Neumann algebras. Journal of Mathematical Analysis and Applications 511, no. 2 (2022) . DOI: 10.1016/j.jmaa.2022.126072  [arxiv]

9. The Balian-Low theorem for locally compact abelian groups and vector bundles. Journal de Mathématiques Pures et Appliquées 139 (2020) 143-176. DOI: 10.1016/j.matpur.2019.12.005 [arxiv]

10. Heisenberg modules as function spaces (with Are Austad). Journal of Fourier Analysis and Applications 26.2  (2020). DOI: 10.1007/s00041-020-09729-7 [arxiv]

11. Time-frequency analysis on the adeles over the rationals (with Mads S. Jakobsen and Franz Luef). Comptes Rendus Mathématique 357 (2019) no. 2, 188-199. DOI: 10.1016/j.crma.2018.12.004 [arxiv]