Drinfeld Coproduct, Quantum Fusion Tensor Category and Applications

The class of quantum affinizations (or quantum loop algebras, see [Dr2, CP3, GKV, VV2, Mi1, N1, Jin, H3]) includes quantum affine algebras and quantum toroidal algebras. In general they have no Hopf algebra structure, but have a “coproduct” (the Drinfeld coproduct) which does not produce tensor products of modules in the usual way because it is defined in a completion. In this paper we propose a new process to produce quantum fusion modules from it : for all quantum affinizations, we construct by deformation and renormalization a new (non semisimple) tensor category Mod. For quantum affine algebras this process is new and different from the usual tensor product. For general quantum affinizations, for example for toroidal algebras, so far, no process to produce fusion modules was known. We derive several applications from it : we construct the fusion of (finitely many) arbitrary l-highest weight modules, and prove that it is always cyclic. We establish exact sequences involving fusion of Kirillov-Reshetikhin modules related to new T -systems extending results of [N4, N3, H5]. Eventually for a large class of quantum affinizations we prove that the subcategory of finite length modules of Mod is stable under the new monoidal bifunctor. 2000 Mathematics Subject Classification: Primary 17B37, Secondary 20G42, 81R50.