A Whittaker category for the Symplectic Lie algebra (2203.14376v1)

Abstract: For any $n\in \mathbb{Z}{\geq 2}$, let $\mathfrak{m}_n$ be the subalgebra of $\mathfrak{sp}{2n}$ spanned by all long negative root vectors $X_{-2\epsilon_i}$, $i=1,\dots,n$. An $\mathfrak{sp}{2n}$-module $M$ is called a Whittaker module with respect to the Whittaker pair $(\mathfrak{sp}{2n},\mathfrak{m}n)$ if the action of $\mathfrak{m}_n$ on $M$ is locally finite, according to a definition of Batra and Mazorchuk. This kind of modules are more general than the classical Whittaker modules defined by Kostant. In this paper, we show that each non-singular block $\mathcal{WH}{\mathbf{a}}^{\mu}$ with finite dimensional Whittaker vector subspaces is equivalent to a module category $\mathcal{W}^{\mathbf{a}}$ of the even Weyl algebra $\mathcal{D}n^{ev}$ which is semi-simple. As a corollary, any simple module in the block $\mathcal{WH}{\mathbf{i}}^{-\frac{1}{2}\omega_n}$ for the fundamental weight $\omega_n$ is equivalent to the Nilsson's module $N_{\mathbf{i}}$ up to an automorphism of $\mathfrak{sp}{2n}$. We also characterize all possible algebra homomorphisms from $U(\mathfrak{sp}{2n})$ to the Weyl algebra $\mathcal{D}_n$ under a natural condition.