The 1-skeleton of a G-manifold M is the set
of points p∈M, where dim
Gp≥dim G−1, and
M is a GKM manifold if the dimension of this 1-skeleton
is 2. M. Goresky, R. Kottwitz, and R. MacPherson show that for
such a manifold this 1-skeleton has the structure of a
"labeled" graph, (Γ,α), and that the
equivariant cohomology ring of M is isomorphic to the
"cohomology ring" of this graph. Hence, if M is
symplectic, one can show that this ring is a free module over
the symmetric algebra
(
*), with
b2i(Γ) generators in dimension
2i,b2i(Γ) being the "combinatorial" 2ith Betti
number of Γ. In this article we show that this
"topological" result is, in fact, a combinatorial result about
graphs.
References
M. F. Atiyah, Convexity and commuting Hamiltonians, Bull. London Math. Soc. 14 (1982), 1--15.
Mathematical Reviews (MathSciNet):
MR642416
M. F. Atiyah and R. Bott, The moment map and equivariant cohomology, Topology 23 (1984), 1--28.
Mathematical Reviews (MathSciNet):
MR721448
N. Berline and M. Vergne, Classes caractéristiques équivariantes. Formule de localisation en cohomologie équivariante, C. R. Acad. Sci. Paris Sér. I Math. 295 (1982), 539--541.
Mathematical Reviews (MathSciNet):
MR685019
I. N. Bernšteĭn, I. M. Gelfand, and S. I. Gelfand, Schubert cells, and the cohomology of the spaces $G/P$, Russian Math. Surveys 28 (1973), 1--26.
A. Bialynicki-Birula, Some theorems on actions of algebraic groups, Ann. of Math. (2) 98 (1973), 480--497.
Mathematical Reviews (MathSciNet):
MR366940
S. Billey, Kostant polynomials and the cohomology ring for $G/B$, Duke Math. J. 96 (1999), 205--224.
S. Billey and M. Haiman, Schubert polynomials for the classical groups, J. Amer. Math. Soc. 8 (1995), 443--482.
A. Borel, Seminar on Transformation Groups, Ann. of Math. Stud. 46, Princeton Univ. Press, Princeton, 1960.
Mathematical Reviews (MathSciNet):
MR116341
M. Brion and C. Procesi, ``Action d'un tore dans une variété projective'' in Operator Algebras, Unitary Representations, Enveloping Algebras, and Invariant Theory (Paris, 1989), Progr. Math. 92, Birkhäuser, Boston, 1990, 509--539.
A. E. Brouwer, A. M. Cohen, and A. Neumaier, Distance-Regular Graphs, Ergeb. Math. Grenzgeb. (3) 18, Springer, Berlin, 1989.
H. Crapo and W. Whiteley, Spaces of stresses, projections and parallel drawings for spherical polyhedra, Beiträge Algebra Geom. 35 (1994), 259--281.
T. Delzant, Hamiltoniens périodiques et images convexes de l'application moment, Bull. Soc. Math. France 116 (1988), 315--339.
Mathematical Reviews (MathSciNet):
MR984900
M. Demazure, Désingularisation des variétés de Schubert généralisées, Ann. Sci. \' Ecole Norm. Sup. (4) 7 (1974), 53--88.
Mathematical Reviews (MathSciNet):
MR354697
W. Fulton, Flags, Schubert polynomials, degeneracy loci, and determinantal formulas, Duke Math. J. 65 (1992), 381--420.
--------, Young Tableaux: With Applications to Representation Theory and Geometry, London Math. Soc. Stud. Texts 35, Cambridge Univ. Press, Cambridge, 1997.
V. Ginzburg, Y. Karshon, and S. Tolman, in preparation.
L. Godinho, Circle actions on symplectic manifolds, Ph.D. dissertation, State University of New York at Stony Brook, 1999.
M. Goresky, R. Kottwitz, and R. MacPherson, Equivariant cohomology, Koszul duality, and the localization theorem, Invent. Math. 131 (1998), 25--83.
V. Guillemin, T. Holm, and C. Zara, GKM-theory on homogeneous manifolds, in preparation.
V. Guillemin and S. Sternberg, Convexity properties of the moment mapping, Invent. Math. 67 (1982), 491--513.
Mathematical Reviews (MathSciNet):
MR664117
--. --. --. --., Birational equivalence in the symplectic category, Invent. Math. 97 (1989), 485--522.
--------, Supersymmetry and Equivariant de Rham Theory, Math. Past Present, Springer, Berlin, 1999.
V. Guillemin and C. Zara, Equivariant de Rham theory and graphs, Asian J. Math. 3 (1999), 49--76.
J. Humphreys, Reflection Groups and Coxeter Groups, Cambridge Stud. Adv. Math. 29, Cambridge Univ. Press, Cambridge, 1990.
N. Jacobson, Cayley numbers and normal simple Lie algebras of type $G$, Duke Math. J. 5 (1939), 775--783.
Mathematical Reviews (MathSciNet):
MR598
F. C. Kirwan, Cohomology of Quotients in Symplectic and Algebraic Geometry, Math. Notes 31, Princeton Univ. Press, Princeton, 1984.
Mathematical Reviews (MathSciNet):
MR766741
A. A. Klyachko, Equivariant bundles over toric varieties, Math. USSR-Izv. 35 (1990), no. 2, 337--375.
S. Kobayashi and K. Nomizu, Foundations of Differential Geometry, Vol. II, Interscience Tracts in Pure Appl. Math. 15, Interscience, New York, 1969.
Mathematical Reviews (MathSciNet):
MR238225
B. Kostant and S. Kumar, The nil Hecke ring and cohomology of $G/P$ for a Kac-Moody group $G$, Adv. in Math. 62 (1986), 187--237.
Mathematical Reviews (MathSciNet):
MR866159
A. Lascoux and M.-P. Schützenberger, Schubert polynomials and the Littlewood-Richardson rule, Lett. Math. Phys. 10 (1985), 111--124.
Mathematical Reviews (MathSciNet):
MR815233
E. Lerman, Symplectic cuts, Math. Res. Lett. 2 (1995), 247--258.
E. Lerman and S. Tolman, Hamiltonian torus actions on symplectic orbifolds and toric varieties, Trans. Amer. Math. Soc. 349 (1997), 4201--4230.
B. H. Lian, K. Liu, and S.-T. Yau, ``Mirror principle: A survey'' in Current Developments in Mathematics (Cambridge, Mass., 1998), International Press, Boston, 1998, 35--65.
I. G. Macdonald, ``Schubert polynomials'' in Surveys in Combinatorics (Guildford, U.K., 1991), London Math. Soc. Lecture Note Ser. 166, Cambridge Univ. Press, Cambridge, 1991, 73--99.
D. McDuff, Examples of simply-connected symplectic non-Kählerian manifolds, J. Differential Geom. 20 (1984), 267--277.
Mathematical Reviews (MathSciNet):
MR772133
E. Meinrenken, Symplectic surgery and the Spin$^c$-Dirac operator, Adv. Math. 134 (1998), 240--277.
R. P. Stanley, Combinatorics and Commutative Algebra, Progr. Math. 41, Birkhäuser, Boston, 1983.
Mathematical Reviews (MathSciNet):
MR725505
S. Tolman and J. Weitsman, The cohomology rings of abelian symplectic quotients, preprint, http://www.arXiv.org/abs/math.DG/9807173.
--. --. --. --., ``On the cohomology rings of Hamiltonian T-spaces'' in Northern California Symplectic Geometry Seminar, Amer. Math. Soc. Transl. Ser. 2 196, Amer. Math. Soc., Providence, 1999, 251--258.