SOLUTIONS OF THE QUANTUM DYNAMICAL YANG-BAXTER EQUATION AND DYNAMICALQUANTUM GROUPS

The quantum dynamical Yang-Baxter (QDYB) equation is a useful generali zation of the quantum Yang-Baxter (QYB) equation. This generalization was introduced by Gervais, Neveu, and Felder. Unlike the QYB equation, the QDYB equation is not an algebraic but a difference equation, with respect to a matrix function rather than a matrix. The QDYB equation and its quasiclassical analogue (the classical dynamical Yang-Baxter e quation) arise in several areas of mathematics and mathematical physic s (conformal field theory, integrable systems, representation theory). The most interesting solution of the QDYB equation is the elliptic so lution, discovered by Felder. In this paper, we prove the first classi fication results for solutions of the QDYB equation. These results are parallel to the classification of solutions of the classical dynamica l Yang-Baxter equation, obtained in our previous paper. All solutions we found can be obtained from Felder's elliptic solution by a limiting process and gauge transformations. Fifteen years ago the quantum Yang -Baxter equation gave rise to the theory of quantum groups. Namely, it turned out that the language of quantum groups (Hopf algebras) is the adequate algebraic language to talk about solutions of the quantum Ya ng-Baxter equation. In this paper we propose a similar language, origi nating from Felder's ideas, which we found to be adequate for the dyna mical Yang-Baxter equation. This is the language of dynamical quantum groups (or h-Hopf algebroids), which is the quantum counterpart of the language of dynamical Poisson groupoids, introduced in our previous p aper.