Abstract. A simpler definition for a class of two-parameter quantum groups associated to semisimple Lie algebras is given in terms of Euler form. Their positive parts turn out to be 2-cocycle deformations of each other under some conditions. An operator realization of the positive part is given.
IntroductionThe notion of quantum groups was introduced by V. Drinfel'd and M. Jimbo, independently, around 1985 in their study of the quantum Yang-Baxter equations. Quantum groups U q (g), depending on a single parameter q, are certain families of Hopf algebras that are deformations of universal enveloping algebras of symmetrizable Kac-Moody algebras. In the early 90s of the last century, much work had been done on their multiparameter generalizations, which can be obtained by twisting the algebra structure via a 2-cocycle on an indexed free abelian group (see [1]) or by twisting the coalgebra structure in the spirit of Drinfeld (see [2], [3]). Note that a 2-cocycle (or a Drinfeld twist) deformation is an important method to yield new (twisted) bialgebras from old ones.Motivated by the work on down-up algebras [4], Benkart and Witherspoon, et al [5,6,7,8] investigated the two-parameter quantum groups of the general linear Lie algebra gl n and the special linear Lie algebra sl n . Later on, Bergeron, Gao and Hu [9, 10] developed the corresponding theory for two-parameter quantum orthogonal and symplectic groups. Recently, Hu et al continued this project (see [11,12] In this note, we give a simpler definition for a class of two-parameter quantum groups U r,s (g) associated to semisimple Lie algebras in terms of the Euler form (or say, Ringel form). As in [5,9,11,12,16,17], these quantum groups also possess the Drinfel'd double structures and the triangular decompositions (see Section 2). As a main point of this note, we show that the positive parts of quantum groups under consideration are 2-cocycle deformations of each other as Q + -graded associative Calgebras if the parameters satisfy certain conditions (see Section 3). This affords an insight into the interrelation between the two-parameter quantum groups we defined and the one-parameter Drinfeld-Jimbo ones. In Section 4, we get an operator realization of the positive part of U r,s (g) by assigning the canonical generators e i 's with some skew differential operators in the sense of Kashiwara ([18]).