Invariants and separating morphisms for algebraic group actions
The first part of this paper is a refinement of Winkelmann’s work on invariant rings and quotients of algebraic group actions on affine varieties, where we take a more geometric point of view. We show that the (algebraic) quotient X//G given by the possibly not finitely generated ring of invariants...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Published: |
Springer-Verlag
2015
|
| Online Access: | https://eprints.nottingham.ac.uk/47067/ |
| _version_ | 1848797460371079168 |
|---|---|
| author | Dufresne, Emilie Kraft, Hanspeter |
| author_facet | Dufresne, Emilie Kraft, Hanspeter |
| author_sort | Dufresne, Emilie |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | The first part of this paper is a refinement of Winkelmann’s work on invariant rings and quotients of algebraic group actions on affine varieties, where we take a more geometric point of view. We show that the (algebraic) quotient X//G given by the possibly not finitely generated ring of invariants is “almost” an algebraic variety, and that the quotient morphism π: X → X//G has a number of nice properties. One of the main difficulties comes from the fact that the quotient morphism is not necessarily surjective. These general results are then refined for actions of the additive group Ga, where we can say much more. We get a rather explicit description of the so-called plinth variety and of the separating variety, which measures how much orbits are separated by invariants. The most complete results are obtained for representations. We also give a complete and detailed analysis of Roberts’ famous example of a an action of Ga on 7-dimensional affine space with a non-finitely generated ring of invariants. |
| first_indexed | 2025-11-14T20:04:13Z |
| format | Article |
| id | nottingham-47067 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| last_indexed | 2025-11-14T20:04:13Z |
| publishDate | 2015 |
| publisher | Springer-Verlag |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-470672020-05-04T17:09:31Z https://eprints.nottingham.ac.uk/47067/ Invariants and separating morphisms for algebraic group actions Dufresne, Emilie Kraft, Hanspeter The first part of this paper is a refinement of Winkelmann’s work on invariant rings and quotients of algebraic group actions on affine varieties, where we take a more geometric point of view. We show that the (algebraic) quotient X//G given by the possibly not finitely generated ring of invariants is “almost” an algebraic variety, and that the quotient morphism π: X → X//G has a number of nice properties. One of the main difficulties comes from the fact that the quotient morphism is not necessarily surjective. These general results are then refined for actions of the additive group Ga, where we can say much more. We get a rather explicit description of the so-called plinth variety and of the separating variety, which measures how much orbits are separated by invariants. The most complete results are obtained for representations. We also give a complete and detailed analysis of Roberts’ famous example of a an action of Ga on 7-dimensional affine space with a non-finitely generated ring of invariants. Springer-Verlag 2015-06-30 Article PeerReviewed Dufresne, Emilie and Kraft, Hanspeter (2015) Invariants and separating morphisms for algebraic group actions. Mathematische Zeitschrift, 280 (1-2). pp. 231-255. ISSN 1432-1823 https://link.springer.com/article/10.1007%2Fs00209-015-1420-0 doi:10.1007/s00209-015-1420-0 doi:10.1007/s00209-015-1420-0 |
| spellingShingle | Dufresne, Emilie Kraft, Hanspeter Invariants and separating morphisms for algebraic group actions |
| title | Invariants and separating morphisms for algebraic group actions |
| title_full | Invariants and separating morphisms for algebraic group actions |
| title_fullStr | Invariants and separating morphisms for algebraic group actions |
| title_full_unstemmed | Invariants and separating morphisms for algebraic group actions |
| title_short | Invariants and separating morphisms for algebraic group actions |
| title_sort | invariants and separating morphisms for algebraic group actions |
| url | https://eprints.nottingham.ac.uk/47067/ https://eprints.nottingham.ac.uk/47067/ https://eprints.nottingham.ac.uk/47067/ |