Immanuel van Santen

activity

20192026

most citedCharacterizing quasi-affine spherical varieties via the automorphism group

1 citations · 2 across the 8 of their papers we have counts for

collaborators

8 papers

math.AG2026

Solvable Automorphism Groups of Varieties

Serge Cantat, Hanspeter Kraft, Andriy Regeta +1

Let $X$ be a variety of dimension $n$ , and let $Aut (X)$ be its automorphism group. When $X$ is quasi-affine, we prove that a solvable subgroup of $Aut (X)$ that is…

math.AG2026

On Ramanujam's Theorem About Finite Dimensional Groups of Automorphisms

Serge Cantat, Hanspeter Kraft, Andriy Regeta +1

Ramanujam's theorem states that any connected finite-dimensional subgroup of the automorphism group $Aut (X)$ of an irreducible variety $X$ is an algebraic group, in a natu…

math.AG2026

Symmetric subrank and its border analogue

Benjamin Biaggi, Jan Draisma, Koen de Nooij +1

The symmetric subrank of homogeneous polynomial is the largest number of terms in a diagonal form to which it can be specialized by a (typically non-invertible) linear variable sub…

math.AG2025

Characterizing Varieties Using Birational Transformations

Nathan Chen, Louis Esser, Andriy Regeta +2

Suppose $X$ is an irreducible complex variety. We show that when $X$ is ruled, the group of birational transformations $B i r (X)$ , as a group, determines $X$ up to birational transfo…

math.AG2024

Group Theoretical Characterizations of Rationality

Andriy Regeta, Christian Urech, Immanuel van Santen

Let X be an irreducible variety and Bir(X) its group of birational transformations. We show that the group structure of Bir(X) determines whether X is rational and whether X is rul…

math.AG2024

The Structure of Algebraic Families of Birational Transformations

Andriy Regeta, Christian Urech, Immanuel van Santen

We give a description of the algebraic families of birational transformations of an algebraic variety X. As an application, we show that the morphisms to Bir(X) given by algebraic…

math.AG2021★ 1 cited

Maximal commutative unipotent subgroups and a characterization of affine spherical varieties

Andriy Regeta, Immanuel van Santen

We describe maximal commutative unipotent subgroups of the automorphism group $Aut (X)$ of an irreducible affine variety $X$ . Further we show that a group isomorphism $\mat…

math.AG2019★ 1 cited

Characterizing quasi-affine spherical varieties via the automorphism group

Andriy Regeta, Immanuel van Santen

Let $G$ be a connected reductive algebraic group. In this note we prove that for a quasi-affine $G$ -spherical variety the weight monoid is determined by the weights of its non-triv…