3 papers
math.RT2026
Spherical subgroups in reductive algebraic groups
Friedrich Knop, Gerhard Roehrle
In a paper from 2015, we determined all spherical affine homogeneous varieties for simple algebraic groups in arbitrary characteristic. The present paper extends this classificatio…
math.RT2024
Reductive group actions
Friedrich Knop, Bernhard Krötz
In this paper, we study rationality properties of reductive group actions which are defined over an arbitrary field of characteristic zero. Thereby, we unify Luna's theory of spher…
math.SG2024
Classification of multiplicity free symplectic representations
Friedrich Knop
Let G be a connected reductive group acting on a finite dimensional vector space V. Assume that V is equipped with a G-invariant symplectic form. Then the ring C[V] of polynomial f…