Reduction of quantum systems with arbitrary first class constraints and Hecke algebras

We propose a method for reduction of quantum systems with arbitrary first class constraints. An appropriate mathematical setting for the problem is homology of associative algebras. For every such an algebra $A$ and its subalgebra B with an augmentation e there exists a cohomological complex which is a generalization of the BRST one. Its cohomology is an associative graded algebra Hk^{*}(A,B) which we call the Hecke algebra of the triple (A,B,e). It acts in the cohomology space H^{*}(B,V) for every left A- module V. In particular the zeroth graded component Hk^{0}(A,B) acts in the space of B- invariants of V and provides the reduction of the quantum system.Comment: 15 pages, LaTeX 2

The geometric meaning of Zhelobenko operators

Let g be the complex semisimple Lie algebra associated to a complex semisimple algebraic group G, b a Borel subalgebra of g, h the Cartan sublagebra contained in b and N the unipotent subgroup of G corresponding to the nilradical n of b. We show that the explicit formula for the extremal projection operator for g obtained by Asherova, Smirnov and Tolstoy and similar formulas for Zhelobenko operators are related to the existence of a birational equivalence N\times h -> b given by the restriction of the adjoint action. Simple geometric proofs of formulas for the "classical" counterparts of the extremal projection operator and of Zhelobenko operators are also obtained.Comment: 9 pages, final versio

An analogue of the operator curl for nonabelian gauge groups and scattering theory

We introduce a new perturbation for the operator curl related to connections with nonabelian gauge groups. We also prove that the perturbed operator is unitary equivalent to the operator curl if the corresponding connection is close enough to the trivial one with respect to a certain topology on the space of connections.Comment: 14 page

Strictly transversal slices to conjugacy classes in algebraic groups

We show that for every conjugacy class O in a connected semisimple algebraic group G over a field of characteristic good for G one can find a special transversal slice S to the set of conjugacy classes in G such that O intersects S and dim O = codim S.Comment: 38 pages; minor modification

Semi-infinite cohomology and Hecke algebras

This paper provides a homological algebraic foundation for generalizations of classical Hecke algebras introduced in math.QA/9805134. These new Hecke algebras are associated to triples of the form (A,B,e), where A is an associative algebra containing subalgebra B with character e. These algebras are connected with cohomology of associative algebras in the sense that for every left A-module V and right A-module W the Hecke algebra associated to triple (A,B,e) naturally acts in the B-cohomology and B-homology spaces of V and W, respectively. We also introduce the semi-infinite cohomology functor for associative algebras and define modifications of Hecke algebras acting in semi-infinite cohomology spaces. We call these algebras semi-infinite Hecke algebras. As an example we realize the W-algebra W(g) associated to a complex semisimple Lie algebra g as a semi-infinite Hecke algebra. Using this realization we explicitly calculate the algebra W(g) avoiding the bosonization technique used by Feigin and Frenkel.Comment: 45 pages, AMSLaTeX, 1 figure using XY-pi

The classical r-matrix method for nonlinear sigma-model

The canonical Poisson structure of nonlinear sigma-model is presented as a Lie-Poisson r-matrix bracket on coadjoint orbits. It is shown that the Poisson structure of this model is determined by some `hidden singularities' of the Lax matrix.Comment: 18 pages, LaTe