Astérisque, n° 246. Geometry of q-hypergeometric functions, quantum affine algebras and elliptic quantum groups

The trigonometric quantized Knizhnik Zamalodchikov ( qKZ ) equation associated with the quantum group Uq (Sl<sub>2</sub>) is a system of linear difference equations with values in a tensor product of Uq (Sl<sub>2</sub>) Verma modules. We solve the equation in terms of multidimensional q -hypergeometric functions and definie a natural isomorphism of the space of solutions and the tensor product of the corresponding evaluation Verma modules over the elliptic quantum group E <sub>p,lambdà</sub>(Sl<sub>2</sub>) where parameters p and lambdà are related to the parameter q of the quantum group Uq (Sl<sub>2</sub>) and the step p of the qKZ equation via p = e<sup>2mp</sup> and q = e<sup>-2mlambdà</sup> .
We construct asymptotic solutions associated with suitable asymptotic zones and compute the transition functions between the asymptotic solutions in terms of the dynamical elliptic R -matrices. This description of the transition functions gives a connection between representation theories of the quantum loop algebra Uq (Sl<sub>2</sub>) and the elliptic quantum group E<sub>micron, lambdà</sub> (Sl<sub>2</sub>) and is analogous to the Kohno-Drinfeld theorem on the monodromy group of the differential Knizhnik-Zamolodchikov equation.
In order to establish these results we construct a discrete Gauss-Manin connection, in particular, a suitable discrete local system, discrete homology and cohomology groups with coefficients in this local system, and identify an associated difference equation with the qKZ equation.