The generalization of Jones polynomial of links to the case of graphs inR
3 is presented. It is constructed as the functor from the category of graphs to the category of representations of the quantum groups.

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Ribbon graphs and their invariants derived from quantum groups

We derive new holonomicq-difference equations for the matrix coefficients of the products of intertwining operators for quantum affine algebra
 representations of levelk. We study the connection opertors between the solutions with different asymptotics and show that they are given by products of elliptic theta functions. We prove that the connection operators automatically provide elliptic solutions of Yang-Baxter equations in the “face” formulation for any type of Lie algebra
 
$$\mathfrak{g}$$

 and arbitrary finite-dimensional representations of
 . We conjecture that these solutions of the Yang-Baxter equations cover all elliptic solutions known in the contexts of IRF models of statistical mechanics. We also conjecture that in a special limit whenq→1 these solutions degenerate again into
 solutions with
 
$$q' = \exp \left( {\frac{{2\pi i}}{{k + g}}} \right)$$

 . We also study the simples examples of solutions of our holonomic difference equations associated to
 
$$U_q (\widehat{\mathfrak{s}\mathfrak{l}(2)})$$

 and find their expressions in terms of basic (orq−)-hypergeometric series. In the special case of spin −1/2 representations, we demonstrate that the connection matrix yields a famous Baxter solution of the Yang-Baxter equation corresponding to the solid-on-solid model of statistical mechanics.

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Quantum affine algebras and holonomic difference equations

Contents §0. Introduction §1. The Yangian §2. The quantum determinant and the centre of §3. The twisted Yangian §4. The Sklyanin determinant and the centre of §5. The quantum contraction and the quantum Liouville formula for the Yangian §6. The quantum contraction and the quantum Liouville formula for the twisted Yangian §7. The quantum determinant and the Sklyanin determinant of block matrices Bibliography

Yangians and Classical Lie Algebras

Lie bialgebras arise as infinitesimal invariants of Poisson Lie groups. A Lie bialgebra is a Lie algebra g with a Lie algebra structure on the dual g∗ which is compatible with the Lie algebra g in a certain sense. For a Poisson group G, the multiplicative Poisson structure π induces a Lie algebra structure on the Lie algebra dual g∗ which makes (g, g∗) into a Lie bialgebra. In fact, there is a one-one correspondence between Poisson Lie groups and Lie bialgebras if the Lie groups are assumed to be simply connected [7], [16], [19]. The importance of Poisson Lie groups themselves arises in part from their role as classical limits of quantum groups [8] and in part because they provide a class of Poisson structures for which the realization problem is tractable [15]. Poisson groupoids were introduced by Weinstein [24] as a generalization of both Poisson Lie groups and the symplectic groupoids which arise in the integration of arbitrary Poisson manifolds [4], [11]. He noted that the Lie algebroid dual A∗G of a Poisson groupoid G itself has a Lie algebroid structure, but did not develop the infinitesimal structure further. In this paper we introduce and study a natural infinitesimal invariant for Poisson groupoids, the Lie bialgebroids of the title. Our ultimate purpose is to develop a Lie theory for Poisson groupoids parallel to that for Poisson groups. In this paper we are primarily concerned with the first half of this process; that is, with the construction of the Lie bialgebroid of a Poisson groupoid. After the preliminary §2, in which we describe the generalization to arbitrary Lie algebroids of the exterior calculus and Schouten calculus, in §3 we define a Lie bialgebroid to be a Lie algebroid A whose dual A∗ is also equipped with a Lie algebroid structure, such that the coboundary operator d∗ : A −→ ∧(A) associated to A∗ satisfies a cocycle equation with respect to Γ(A), the Lie algebra of sections of A. This is clearly a straightforward extension of the concept of a Lie bialgebra [16] but cannot be formalized in Lie algebroid cohomological terms since there is no satisfactory adjoint representation for a general Lie algebroid. Most of §3 is devoted to proving that this definition is self-dual: if (A,A∗) is a Lie bialgebroid, then (A∗, A) is also. In §4, we briefly consider the special case of Lie bialgebroids satisfying a triangularity condition, which include some important examples such as the usual triangular Lie bialgebras and Lie bialgebroids associated to Poisson manifolds. The techniques used in §§2–4 are similar to those known for Lie bialgebras. It would be possible, by suitably generalizing the proof for Poisson groups, to prove

Lie bialgebroids and Poisson groupoids

We describe Hopf algebras which are central extensions of quantum current groups. For a special value of the central charge, we describe Casimir elements in these algebras. New types of generators for quantum current algebra and its central extension for quantum simple Lie groups, are obtained. The application of our construction to the elliptic case is also discussed.

M. A. Semenov-Tian-Shansky

Papers

Central extensions of quantum current groups

Quantum R-matrices and factorization problems