39 citations · 61 across the 4 of their papers we have counts for
7 papers
Classification of smooth affine spherical varieties
Friedrich Knop, Bart Van Steirteghem
Let G be a complex reductive group. A normal G-variety X is called spherical if a Borel subgroup of G has a dense orbit in X. Of particular interest are spherical varieties which a…
Graded cofinite rings of differential operators
Friedrich Knop
We classify subalgebras of a ring of differential operators which are big in the sense that the extension of associated graded rings is finite. We show that these subalgebras corre…
On the Kazhdan-Lusztig basis of a spherical Hecke algebra
Friedrich Knop
Lusztig proved that the Kazhdan-Lusztig basis of a spherical Hecke algebra can be essentially identified with the Weyl characters of the Langlands dual group. We generalize this re…
On Noether's and Weyl's bound in positive characteristic
Friedrich Knop
In this note we generalize several well known results concerning invariants of finite groups from characteristic zero to positive characteristic not dividing the group order. The f…
Convexity of Hamiltonian manifolds
Friedrich Knop
Let K be a connected Lie group and M a Hamiltonian K-manifold. In this paper, we introduce the notion of convexity of M. It implies that the momentum image is convex, the moment ma…
A connectedness property of algebraic moment maps
Friedrich Knop
Let a connected reductive group G act on the smooth connected variety X. The cotangent bundle of X is a Hamiltonian G-variety. We show that its "total moment map" has connected fib…