Conjugacy classes in Weyl groups and q-W algebras

We define noncommutative deformations $W_q^s(G)$ of algebras of functions on certain (finite coverings of) transversal slices to the set of conjugacy classes in an algebraic group $G$ which play the role of Slodowy slices in algebraic group theory. The algebras $W_q^s(G)$ called q-W algebras are labeled by (conjugacy classes of) elements $s$ of the Weyl group of $G$. The algebra $W_q^s(G)$ is a quantization of a Poisson structure defined on the corresponding transversal slice in $G$ with the help of Poisson reduction of a Poisson bracket associated to a Poisson-Lie group $G^*$ dual to a quasitriangular Poisson-Lie group. The algebras $W_q^s(G)$ can be regarded as quantum group counterparts of W-algebras. However, in general they are not deformations of the usual W-algebras.Comment: 48 pages; some arguments in the proof of Proposition 12.2 are clarifie

Geometry of Hyper-K\"ahler Connections with Torsion

The internal space of a N=4 supersymmetric model with Wess-Zumino term has a connection with totally skew-symmetric torsion and holonomy in \SP(n). We study the mathematical background of this type of connections. In particular, we relate it to classical Hermitian geometry construct homogeneous as well as inhomogeneous examples, characterize it in terms of holomorphic data, develop its potential theory and reduction theory.Comment: 21 pages, LaTe