- Commit
- fc7709c45f8cacdba8bde66503ebd9e7a75ca73a
- Parent
- 43a49d94323438d680a965b59913e9146fad5b10
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Added lemmas necessary to prove the existance of Mathieu's Ext extension
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Added lemmas necessary to prove the existance of Mathieu's Ext extension
1 file changed, 66 insertions, 1 deletion
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/mathieu.tex | 67 | 66 | 1 |
diff --git a/sections/mathieu.tex b/sections/mathieu.tex @@ -303,6 +303,71 @@ \section{Existance of Coherent Extensions} +% TODO: Add the results on Ore's localization + +% TODO: Define what a set commuting roots is +\begin{lemma}\label{thm:nice-basis-for-inversion} + Let \(V\) be an irreducible infinite-dimensional admissible + \(\mathfrak{g}\)-module. There is a basis \(\Sigma = \{\alpha_1, \ldots, + \alpha_n\}\) of \(Q\) consisting a commuting roots and such that the elements + \(F_{\alpha_i}\) all act injectively on \(V\). +\end{lemma} + +\begin{corollary} + Let \(\Sigma\) be as in lemma~\ref{thm:nice-basis-for-inversion} and + \((F_\alpha : \alpha \in \Sigma) \subset \mathcal{U}(\mathfrak{g})\) be + the multiplicative subset generated by \(F_\alpha\), \(\alpha \in F_\alpha\). + The \(K\)-algebra \(\mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in + \Sigma)}\) is well defined and the localization map + \begin{align*} + V & + \to \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in \Sigma)} + \otimes V \\ + u & \mapsto 1 \otimes u + \end{align*} + is injective. +\end{corollary} + +\begin{proposition} + Let \(V\) be an irreducible infinite-dimensional admissible + \(\mathfrak{g}\)-module. Then \(V\) is contained in a weight module \(M\) of + degree \(d\) such that \(\operatorname{supp} M = Q + \operatorname{supp} V\) + and \(\dim M_\lambda = d\) for all \(\lambda \in \operatorname{supp} M\). +\end{proposition} + +% TODO: Remark that any module over the localization is a g-module if we +% restrict it via the localization map, wich is injective in this case +\begin{proposition} + There is a family of automorphisms \(\{F_{\Sigma}^\lambda : + \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in \Sigma)} \to + \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in \Sigma)}\}_{\lambda \in + \mathfrak{h}^*}\) such that + \begin{enumerate} + \item \(F_{\Sigma}^{k_1 \alpha_1 + \cdots k_n \alpha^n}(u) = + F_{\alpha_1}^{k_1} \cdots F_{\alpha_n}^{k_n} u F_{\alpha_1}^{- k_n} + \cdots F_{\alpha_n}^{- k_1}\) for all \(u \in + \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in \Sigma)}\) and \(k_1, + \ldots, k_n \in \mathbb{Z}\). + + \item For each \(u \in \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in + \Sigma)}\) the map + \begin{align*} + \mathfrak{h}^* & + \to \mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in \Sigma)} \\ + \lambda & \mapsto F_\Sigma^\lambda(u) + \end{align*} + is polynomial. + + \item If \(M\) is the \(\mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in + \Sigma)}\)-module \(\mathcal{U}(\mathfrak{g})_{(F_\alpha : \alpha \in + \Sigma)} \otimes V\), \(\lambda, \mu \in \mathfrak{h}^*\) and + \(F_\Sigma^\lambda M\) is the \(\mathcal{U}(\mathfrak{g})_{(F_\alpha : + \alpha \in \Sigma)}\)-module \(M\) twisted by the automorphism + \(F_\Sigma^\lambda\) then \(M_\mu = (F_\Sigma^\lambda M)_{\mu + + \lambda}\). + \end{enumerate} +\end{proposition} + \begin{theorem}[Mathieu] Let \(V\) be an infinite-dimensional admissible irreducible \(\mathfrak{g}\)-module of degree \(d\). There exists a unique semisimple @@ -311,7 +376,7 @@ \(\mathcal{M}^{\operatorname{ss}} \cong \operatorname{Ext}(V)\). \end{theorem} -\begin{proposition} +\begin{proposition}[Mathieu] The central characters of the irreducible submodules of \(\operatorname{Ext}(V)\) are all the same. \end{proposition}