Descriptions of strongly multiplicity free representations for simple Lie algebras

Let $\mathfrak{g}$ be a simple Lie algebra over the complex numbers $\mathbb{C}$. Let $Z(\mathfrak{g})$ be the center of the universal enveloping algebra $U(\mathfrak{g})$. Denote by $V_\lambda$ the finite-dimensional simple $\mathfrak{g}$-module with highest weight $\lambda$. Lehrer and Zhang defined the notion of strongly multiplicity free representations for simple Lie algebras motivited by studying the structure of the endomorphism algebras $End _{ U(\mathfrak{g})}(V_\lambda^{\otimes r})$in terms of the quotients of Kohno's infinitesimal braid algebra. Kostant introduced the $\mathfrak{g}$ -invariant endomorphism algebras $R_\lambda= (End V_\lambda\otimes U(\mathfrak{g}))^\mathfrak{g}$ and $R_{\lambda,\pi}=(End V_\lambda\otimes \pi[U(\mathfrak{g})])^\mathfrak{g}.$ In this paper, we give some other criterion for a multiplicity free representation to be a strongly multiplicity free representation for simple Lie algebras by classifing the pairs $(\mathfrak{g}, V_\lambda)$, which are multiplicity free irreducible modules and for such pairs, $R_\lambda$ and $R_{\lambda,\pi}$ are generated by generalizations of the quadratic Casimimir elements of $Z(\mathfrak{g})$