Equivariant cohomology, homogeneous spaces and graphs

The focus of this thesis is manifolds with group actions, in particular symplectic manifolds with Hamiltonian torus actions. We investigate the relationship between the equivariant cohomology of the manifold M and the fixed point data of the torus action. We are interested in understanding the topology of the space of T-orbits in M. In particular, we explore aspects of this topology which are determined by data from the image of a moment map [Phi] : M [right arrow] t* associated to the Hamiltonian action. To better understand the orbit space, we apply the algebraic techniques of equivariant cohomology to the study these systems further. Equivariant cohomology associates to a manifold with a G-action a ring H*G(M). Much of the topology of the orbit space is encoded in the equivariant cohomology ring H*G(M). In 1998, Goresky, Kottwitz and MacPherson provided a new method for computing this ring. Their method associates to this orbit space a graph [Gamma] whose vertices are the zero-dimensional orbits and edges the connected components of the set of one-dimensional orbits. The ring H*G(M) can then be computed combinatorially in terms of the data incorporated in [Gamma]. The strength of this construction is that it makes the computation of equivariant cohomology into a combinatorial computation, rather than a topological one. In the projects described herein, we apply the GKM theory to the case of homogeneous spaces by studying the combinatorics of their associated graphs. We exploit this theory to understand the geometry of homogeneous spaces with non-zero Euler characteristic.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mathematics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Holm, Tara Suzanne, 1975-

Advisor dc:contributor.advisor

• Victor Guillemin.

• Mathematics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8463

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8463