On Quasi-Hopf superalgebras

In this work we investigate several important aspects of the structure theory of the recently introduced quasi-Hopf superalgebras (QHSAs), which play a fundamental role in knot theory and integrable systems. In particular we introduce the opposite structure and prove in detail (for the graded case) Drinfeld's result that the coproduct $\Delta ' \equiv (S\otimes S)\cdot T\cdot \Delta \cdot S^{-1}$ induced on a QHSA is obtained from the coproduct $\Delta$ by twisting. The corresponding ``Drinfeld twist'' $F_D$ is explicitly constructed, as well as its inverse, and we investigate the complete QHSA associated with $\Delta'$. We give a universal proof that the coassociator $\Phi'=(S\otimes S\otimes S)\Phi_{321}$ and canonical elements $\alpha' = S(\beta),$ $\beta' = S(\alpha)$ correspond to twisting the original coassociator $\Phi = \Phi_{123}$ and canonical elements $\alpha,\beta$ with the Drinfeld twist $F_D$. Moreover in the quasi-triangular case, it is shown algebraically that the R-matrix $R' = (S\otimes S)R$ corresponds to twisting the original R-matrix $R$ with $F_D$. This has important consequences in knot theory, which will be investigated elsewhere.