5 papers
On Normalizers of Parabolic Subgroups of Quaternionic Reflection Groups
Gerhard Roehrle, Johannes Schmitt
By work of Howlett and Muraleedaran--Taylor, a parabolic subgroup of a real or complex reflection group always admits a complement in its normalizer. In this note, we investigate t…
Parabolic Normalizers in Finite Coxeter Groups as Subdirect Products
J. Matthew Douglass, Götz Pfeiffer, Gerhard Roehrle
We revisit the structure of the normalizer of a parabolic subgroup in a finite Coxeter group , originally described by Howlett. Building on Howlett's Lemma, which p…
MAT-Freeness is not combinatorial
Torsten Hoge, Gerhard Roehrle
We show that the notion of MAT-freeness for hyperplane arrangements depends on the underlying field. In particular, MAT-freeness is not combinatorial.
On Universal derivations for multiarrangements
Takuro Abe, Shota Maehara, Gerhard Roehrle +1
The study of universal derivations for arbitrary multiarrangements and multiplicity functions was initiated by Abe, Röhrle, Stump, and Yoshinaga in 2024 which focused on arrangeme…
Invariants in the cohomology of the complement of quaternionic reflection arrangements
Lorenzo Giordani, Gerhard Roehrle, Johannes Schmitt
Let be a hyperplane arrangement in a vector space and a group fixing . In case when is a complex reflection group and $\mathcal A=\m…