Alice Rogers (King's College, London)
BRST cohomology provides a method for quantizing theories with symmetry. Extra fields known as ghosts are introduced. Certain theories have what is known as a reducible symmetry, and can be quantized by the introduction of further fields, ghosts for ghosts. This talk describes how this scheme can be understood in the Hamiltonian setting, using symplectic geometry, in terms BRST cohomology which is equivariant with respect to the subgroup corresponding to the reducibility.