1998/05/12 by J. M. Drezet, Jean–Marc Drézet, Drezet, J. M. +3
Mathematics · #14D20 (Primary) 14L30 (Secondary) #Advanced Topics in Algebra #Algebraic Geometry (math.AG) #Algebraic structures and combinatorial models #Commutative Algebra and Its Applications #FOS: Mathematics #math.AG #msc:14D20 #msc:14L30
paper · pdf · doi:10.48550/arxiv.math/9805059
Examples and a new section added, references added, 75 pages, 2 figures, Latex2e. To appear in Annals de l'Institut Fourier
openalex publication_date 1998/05/12 · arxiv created 2002/07/11 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We extend the methods of geometric invariant theory to actions of non--reductive groups in the case of homomorphisms between decomposable sheaves whose automorphism groups are non--reductive. Given a linearization of the natural action of the group \Aut(E)×\Aut(F) on Hom(E,F), a homomorphism is called stable if its orbit with respect to the unipotent radical is contained in the stable locus with respect to the natural reductive subgroup of the automorphism group. We encounter effective numerical conditions for a linearization such that the corresponding open set of semi-stable homomorphisms admits a good and projective quotient in the sense of geometric invariant theory, and that this quotient is in addition a geometric quotient on the set of stable homomorphisms.