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arXiv 0710.0906math.RT
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有界广义Harish-Chandra模

Bounded generalized Harish-Chandra modules

Ivan Penkov, Vera Serganova

摘要:

设$\gg$是复约化李代数,$\kk\subset\gg$是$\gg$子代数中的任意约化.我们称一个$(\gg,\kk)$ -模$M$是有界的,如果$M$的$\kk$ -重数是一致有界的.本文对有界简单$(\gg,\kk)$ -模进行了一般性的研究。证明了子代数$\kk$有界的一个强必要条件(推论\ref{cor1.6}),即允许一个无限维有界的简单$(\gg,\kk)$ -模,进而建立了子代数$\kk$有界的一个充分条件(定理\ref{thGroups2}).从而我们能够对$\gg=\sl(n)$的所有极大有界约化子代数进行分类.本文的后半部分详细地描述了简单有界无限维$(\gg,\sl(2))$ -模,特别是计算了它们的特征标和极小$\sl(2)$ -型。证明了如果$\sl(2)$是$\gg$的一个有界子代数,且不包含在$\gg$的一个真理想中,则$\gg\simeq \sl(2)\oplus \sl(2), \sl(3),\sp(4)$ ;总之,直到共轭为止,$\sl(2)$作为一个有界子代数有五种可能的嵌入到$\gg$中.在其中两种情况下,$\sl(2)$是对称子代数,并且关于简单有界$(\gg,\sl(2))$ -模的许多结果是已知的。我们的结果是全新的一种情况是主$\sl(2)$ -子代数在$\sp(4)$的情况。

英文摘要:

Let $\gg$ be a complex reductive Lie algebra and $\kk\subset\gg$ be any reductive in $\gg$ subalgebra. We call a $(\gg,\kk)$-module $M$ bounded if the $\kk$-multiplicities of $M$ are uniformly bounded. In this paper we initiate a general study of simple bounded $(\gg,\kk)$-modules. We prove a strong necessary condition for a subalgebra $\kk$ to be bounded (Corollary \ref{cor1.6}), i.e. to admit an infinite-dimensional simple bounded $(\gg,\kk)$-module, and then establish a sufficient condition for a subalgebra $\kk$ to be bounded (Theorem \ref{thGroups2}). As a result we are able to classify all maximal bounded reductive subalgebras of $\gg=\sl(n)$. In the second half of the paper we describe in detail simple bounded infinite-dimensional $(\gg,\sl(2))$-modules, and in particular compute their characters and minimal $\sl(2)$-types. We show that if $\sl(2)$ is a bounded subalgebra of $\gg$ which is not contained in a proper ideal of $\gg$, then $\gg\simeq \sl(2)\oplus \sl(2), \sl(3),\sp(4)$; alltogether, up to conjugation there are five possible embeddings of $\sl(2)$ as a bounded subalgebra into $\gg$ as above. In two of these cases $\sl(2)$ is a symmetric subalgebra, and many results about simple bounded $(\gg,\sl(2))$-modules are known. A case where our results are entirely new is the case of a principal $\sl(2)$-subalgebra in $\sp(4)$.

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