Abstract
In this paper we deal with a Hamiltonian action of a reductive algebraic group G on an irreducible normal affine Poisson variety X. We study the quotient morphism \({\mu_{G,X}//G : X//G \rightarrow \mathfrak{g} //G}\) of the moment map \({\mu_{G,X} : X\rightarrow \mathfrak{g}}\) . We prove that for a wide class of Hamiltonian actions (including, for example, actions on generically symplectic varieties) all fibers of the morphism μ G,X //G have the same dimension. We also study the “Stein factorization” of μ G,X //G. Namely, let C G,X denote the spectrum of the integral closure of \({\mu_{G,X}^{*}(\mathbb{K}[\mathfrak{g}]^G)}\) in \({\mathbb{K}(X)^G}\) . We investigate the structure of the \({\mathfrak{g} //G}\) -scheme C G,X . Our results partially generalize those obtained by F. Knop for the actions on cotangent bundles and symplectic vector spaces.
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Arnold, V.I., Givental, A.B.: Symplectic geometry. Itogi nauki i techniki. Sovr. probl. matem. Fund. napr., 4, 7-140. VINITI, Moscow, 1985 (in Russian). English translation in: “Dynamical Systems IV”, Encyclopaedia of Mathematical Sciences, 4. Springer Verlag, Berlin (1990)
Bourbaki, N.: Groupes et algèbres de Lie. Chap. 7,8. Hermann, Paris (1975)
Cannas de Silva, A., Weinstein, A.: Geometric models for noncommutative algebras. Berkeley Math. Lecture Notes AMS (1999)
Chevalley, C.: Foundaments de la géométrie algébrique. Paris (1958)
Danilov, V.I.: Algebraic varieties and schemes. Itogi nauki i techniki. Sovr. probl. matem. Fund. napr., 23, 172-302. VINITI, Moscow (1988) (in Russian). English translation in: Algebraic geometry 1, Encyclopaedia of Mathematical Sciences, 23, Springer Verlag, Berlin (1994)
Grosshans F.: The invariants of unipotent radicals of parabolic subgroups. Invent. Math. 73, 1–9 (1983)
Guillemin V., Sternberg Sh.: Symplectic Techniques in Physics. Cambridge University Press, Cambridge (1984)
Kaledin D.: Normalization of a Poisson algebra is Poisson. Proc. Steklov Inst. Math. 264, 70–73 (2009)
Kirwan F.: Convexity properties of the moment mapping III. Invent. Math. 77, 547–552 (1984)
Knop F.: Weylgruppe und Momentabbildung. Invent. Math. 99, 1–23 (1990)
Knop F.: The assymptotic behaviour of invariant collective motion. Invent. Math. 114, 309–328 (1994)
Knop, F.: Weyl groups of Hamiltonian manifolds, I. Preprint. arXiv.math.dg-ga/9712010 (1997)
Knop F.: A connectedness property of algebraic moment maps. J. Algebra 258, 122–136 (2002)
Knop F.: Invariant functions on symplectic representations. J. Algebra 313, 223–251 (2007)
Kraft H.: Geometrishe Methoden in der Invarianttheorie. Viewveg, Braunschweig/Wiesbaden (1985)
Lang, S.: Algebra, 3rd edn. Addison-Wesley, Reading (1993)
Losev, I.: On fibers of algebraic invariant moment maps. Preprint, arXiv:math/0703296. Accepted by Transform. Groups
Milne J.: Etale cohomolgy. Princeton Math. Series, vol. 33. Pricenton University Press, Princeton (1980)
Marsden J., Weinstein A.: Reduction of symplectic manifolds with symmetry. Rep. Math. Phys. 5, 121–130 (1974)
Polishchuk A.: Algebraic geometry of Poisson brackets. J. Math. Sci. 84, 1413–1444 (1997)
Popov, V.L.: Stability criteria for the action of a semisimple group on a factorial manifold. Izv. Akad. Nauk. SSSR, Ser. Mat. 34, 523–531 (1970). English translation in: Math. USSR, Izv. 4, 527–535 (1971)
Popov, V.L., Vinberg, E.B.: On a class of homogeneous affine varieties. Izv. Akad. Nauk SSSR, Ser. Mat. 36, 749–764 (1972) (in Russian). English translation: Math. USSR, Izv. 6, 743–758 (1973)
Popov, V.L., Vinberg, E.B.: Invariant theory. Itogi nauki i techniki. Sovr. probl. matem. Fund. napr., 55. VINITI, Moscow, 137–309 (1989) (in Russian). English translation in: Algebraic geometry 4, Encyclopaedia of Mathematical Sciences, 55. Springer, Berlin (1994)
Sumihiro H.: Equivariant completion. J. Math. Kyoto Univ. 14, 1–28 (1974)
Timashev, D.A.: Equivariant symplectic geometry of cotangent bundles II. Preprint. arXiv:math. AG/0502284 (2004)
Vinberg E.B.: Invariant linear connections on a homogeneous space. Tr. Moskov. Mat. Obshch. 9, 191–210 (1960)
Vinberg E.B.: Equivariant symplectic geometry of cotangent bundles. Mosc. Math. J. 1, 287–299 (2001)
Vinberg, E.B.: Commutative homogeneous spaces and coisotropic symplectic actions. Usp. Mat. Nauk 56, 3–62 (2001) (in Russian). English translation in: Russ. Math. Surveys 56, 1–60 (2001)
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Losev, I.V. Algebraic Hamiltonian actions. Math. Z. 263, 685–723 (2009). https://doi.org/10.1007/s00209-009-0587-7
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DOI: https://doi.org/10.1007/s00209-009-0587-7