68 research outputs found
Homogeneous Fedosov Star Products on Cotangent Bundles I: Weyl and Standard Ordering with Differential Operator Representation
In this paper we construct homogeneous star products of Weyl type on every
cotangent bundle by means of the Fedosov procedure using a symplectic
torsion-free connection on homogeneous of degree zero with respect to
the Liouville vector field. By a fibrewise equivalence transformation we
construct a homogeneous Fedosov star product of standard ordered type
equivalent to the homogeneous Fedosov star product of Weyl type.
Representations for both star product algebras by differential operators on
functions on are constructed leading in the case of the standard ordered
product to the usual standard ordering prescription for smooth complex-valued
functions on polynomial in the momenta (where an arbitrary fixed
torsion-free connection on is used). Motivated by the flat case
another homogeneous star product of Weyl type corresponding to the
Weyl ordering prescription is constructed. The example of the cotangent bundle
of an arbitrary Lie group is explicitly computed and the star product given by
Gutt is rederived in our approach.Comment: 31 pages, LaTeX2e, no picture
BRST Cohomology and Phase Space Reduction in Deformation Quantisation
In this article we consider quantum phase space reduction when zero is a
regular value of the momentum map. By analogy with the classical case we define
the BRST cohomology in the framework of deformation quantization. We compute
the quantum BRST cohomology in terms of a `quantum' Chevalley-Eilenberg
cohomology of the Lie algebra on the constraint surface. To prove this result,
we construct an explicit chain homotopy, both in the classical and quantum
case, which is constructed out of a prolongation of functions on the constraint
surface. We have observed the phenomenon that the quantum BRST cohomology
cannot always be used for quantum reduction, because generally its zero part is
no longer a deformation of the space of all smooth functions on the reduced
phase space. But in case the group action is `sufficiently nice', e.g. proper
(which is the case for all compact Lie group actions), it is shown for a
strongly invariant star product that the BRST procedure always induces a star
product on the reduced phase space in a rather explicit and natural way. Simple
examples and counter examples are discussed.Comment: LaTeX2e, 34 pages, revised version: minor changes and corrected typo
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