Shapovalov elements of classical and quantum groups

Abstract: Shapovalov elements $\theta <em>{\beta,m}$ of the classical or quantized universal enveloping algebra of a simple Lie algebra $\mathfrak{g}$ are parameterized by a positive root $\beta$ and a positive integer $m$. They relate the highest vector of a reducible Verma module with highest vectors of its submodules. We obtain a factorization of $\theta</em>{\beta,m}$ to a product of $\theta_{\beta,1}$ and calculate $\theta_{\beta,1}$ as a residue of a matrix element of the inverse Shapovalov form via a generalized Nigel-Moshinsky algorithm. This way we explicitly express $\theta_{\beta,m}$ of a classical simple Lie algebra through the Cartan-Weyl basis in $\mathfrak{g}$. In the case of quantum groups, we give an analogous formulation through the entries of the R-matrix (quantum $L$-operator) in fundamental representations.