Typical blocks of the category $\mathcal O$ and Whittaker modules for Takiff superalgebras

Chih-Whi Chen, Yongjie Wang

Published 2024-04-11Version 1

We study the simplicity of Kac induced modules over the $\ell$-th Takiff superalgebras $\widetilde{\mathfrak g}_\ell:= \widetilde{\mathfrak g}\otimes \mathbb C[\theta]/(\theta^{\ell+1})$, for $\ell>0$, associated with the Lie superalgebras $\widetilde{\mathfrak g}$ of type I. We formulate a general notion of typical weights and typical Jordan blocks of the category $\mathcal O$ for $\widetilde{\mathfrak g}_\ell$ associated with Lie superalgebras $\mathfrak{gl}(m|n)$, $\mathfrak{osp}(2|2n)$ and $\mathfrak{pe}(n)$. For Lie superalgebras $\mathfrak{gl}(m|n)$ and $\mathfrak{osp}(2|2n)$, we establish an equivalence from an arbitrary typical Jordan block of the category $\mathcal O$ for $\widetilde{\mathfrak g}_\ell$ to a Jordan block of the category $\mathcal O$ for the even subalgebra of $\widetilde{\mathfrak g}_\ell$. This provides a solution to the problem of determining the composition multiplicities of the Verma modules over $\widetilde{\mathfrak g}_\ell$ with typical highest weights. We also investigate non-singular Whittaker modules over these Takiff superalgebras. In particular, we obtain a classification of non-singular simple Whittaker modules and a criterion for simplicity of non-singular standard Whittaker modules.