Generic Gelfand-Tsetlin modules of quantized and classical orthogonal algebras

Abstract

The $q$-deformed associative algebra $U_q'(\mathfrak{so}_n)$ is an example of an $\imath$quantum group. Finite-dimensional simple modules over $U_q'(\mathfrak{so}_n)$ were constructed by Gavrilik and Klimyk which limit to finite-dimensional simple modules over the universal enveloping algebra $U(\mathfrak{so}_n)$ as $q \to 1$. These modules are examples of Gelfand-Tsetlin modules since they are equal to the direct sum of common finite-dimensional eigenspaces under the action of a commutative subalgebra called the Gelfand-Tsetlin subalgebra $\Gamma \subset U_q'(\mathfrak{so}_n)$. In this thesis we begin to study the category of Gelfand-Tsetlin modules over $U_q'(\mathfrak{so}_n)$, which contains the category of finite-dimensional modules. Following the example of Drozd, Futorny and Ovsienko for $U(\mathfrak{gl}_n)$; Mazorchuk and Turowska for $U_q(\mathfrak{gl}_n)$; and Mazorchuk for $U(\mathfrak{so}_n)$; we construct infinite-dimensional analogs to the Gavrilik-Klimyk classical $U_q'(\mathfrak{so}_n)$-modules by removing the conditions on the combinatorial patterns parameterizing the bases. We call these generic Gelfand-Tsetlin modules. We find upper bounds for lengths of these modules for $n=3$ and $n=4$. Taking the limit as $q \to 1$, we obtain generic Gelfand-Tsetlin modules over $U(\mathfrak{so}_n)$ whose matrix coefficients are rational functions, thus extending the work of Mazorchuk. We use these large new families of modules to embed $U_q'(\mathfrak{so}_n)$ and $U(\mathfrak{so}_n)$ into skew group algebras of shift operators. These embeddings map the Gelfand-Tsetlin subalgebras to certain invariant algebras under the actions of the direct products of ($q$-)Weyl groups. Lastly, we use this fact to show the Gelfand-Tsetlin subalgebras are Harish-Chandra subalgebras, as defined by Drozd-Futorny-Ovsienko.