- Commit
- e50e8bf32b7567d761cc919db04d66e0dbc87e02
- Parent
- 3e715aa9e38b35b210b083eec54181bed415cdd7
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Changed the notation for elements of the Weyl group
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Changed the notation for elements of the Weyl group
2 files changed, 26 insertions, 24 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/mathieu.tex | 7 | 4 | 3 |
Modified | sections/semisimple-algebras.tex | 43 | 22 | 21 |
diff --git a/sections/mathieu.tex b/sections/mathieu.tex @@ -283,12 +283,13 @@ relationship is well understood. Namely, Fernando himself established\dots \mathfrak{g}\) is another parabolic subalgebra, \(V\) is an irreducible cuspidal \(\mathfrak{p}\)-module and \(W\) is an irreducible cuspidal \(\mathfrak{p}'\)-module then \(L_{\mathfrak{p}}(V) \cong - L_{\mathfrak{p}'}(W)\) if, and only if \(\mathfrak{p}' = \mathfrak{p}^w\) and - \(W \cong V^w\) for some \(w \in \mathcal{W}_V\), where + L_{\mathfrak{p}'}(W)\) if, and only if \(\mathfrak{p}' = + \mathfrak{p}^\sigma\) and \(W \cong V^\sigma\) for some \(\sigma \in + \mathcal{W}_V\), where \[ \mathcal{W}_V = \langle - T_\beta : \beta \in \Sigma, H_\beta + \mathfrak{u} + \sigma_\beta : \beta \in \Sigma, H_\beta + \mathfrak{u} \ \text{is central in}\ \mfrac{\mathfrak{p}}{\mathfrak{u}} \ \text{and}\ H_\beta\ \text{acts as a positive integer in}\ V \rangle
diff --git a/sections/semisimple-algebras.tex b/sections/semisimple-algebras.tex @@ -519,30 +519,31 @@ in the \(\mathfrak{sl}_2(K)\)-module \(\bigoplus_k V_{\lambda - k \alpha}\). This has a number of important consequences. For instance\dots -% TODO: Change the notation for T_alpha \begin{corollary} - If \(\alpha \in \Delta^+\) and \(T_\alpha : \mathfrak{h}^* \to + If \(\alpha \in \Delta^+\) and \(\sigma_\alpha : \mathfrak{h}^* \to \mathfrak{h}^*\) is the reflection in the hyperplane perpendicular to \(\alpha\) with respect to the Killing form, the weights of \(V\) occuring in - the line joining \(\lambda\) and \(T_\alpha\) are precisely the \(\mu \in P\) - lying between \(\lambda\) and \(T_\alpha \lambda\). + the line joining \(\lambda\) and \(\sigma_\alpha\) are precisely the \(\mu + \in P\) lying between \(\lambda\) and \(\sigma_\alpha(\lambda)\). \end{corollary} \begin{proof} - Notice that any \(\mu \in P\) in the line joining \(\lambda\) and \(T_\alpha - \lambda\) has the form \(\mu = \lambda - k \alpha\) for some \(k\), so that - \(V_\mu\) corresponds the eigenspace associated with the eigenvalue - \(\lambda(H_\alpha) - 2k\) of the action of \(h\) in \(\bigoplus_k V_{\lambda - - k \alpha}\). If \(\mu\) lies between \(\lambda\) and \(T_\alpha \lambda\) - then \(k\) lies between \(0\) and \(\lambda(H_\alpha)\), in which case - \(V_\mu \neq 0\) and therefore \(\mu\) is a weight. - - On the other hand, if \(\mu\) does not lie between \(\lambda\) and \(T_\alpha - \lambda\) then either \(k < 0\) or \(k > \lambda(H_\alpha)\). Suppose \(\mu\) - is a weight. In the first case \(\mu \succ \lambda\), a contradiction. On the - second case the fact that \(V_\mu \ne 0\) implies \(V_{\lambda + (k - - \lambda(H_\alpha)) \alpha} \ne 0 = V_{T_\alpha \mu}\), which contradicts the - fact that \(V_{\lambda + \ell \alpha} = 0\) for all \(\ell \ge 0\). + Notice that any \(\mu \in P\) in the line joining \(\lambda\) and + \(\sigma_\alpha(\lambda)\) has the form \(\mu = \lambda - k \alpha\) for some + \(k\), so that \(V_\mu\) corresponds the eigenspace associated with the + eigenvalue \(\lambda(H_\alpha) - 2k\) of the action of \(h\) in \(\bigoplus_k + V_{\lambda - k \alpha}\). If \(\mu\) lies between \(\lambda\) and + \(\sigma_\alpha(\lambda)\) then \(k\) lies between \(0\) and + \(\lambda(H_\alpha)\), in which case \(V_\mu \neq 0\) and therefore \(\mu\) + is a weight. + + On the other hand, if \(\mu\) does not lie between \(\lambda\) and + \(\sigma_\alpha(\lambda)\) then either \(k < 0\) or \(k > + \lambda(H_\alpha)\). Suppose \(\mu\) is a weight. In the first case \(\mu + \succ \lambda\), a contradiction. On the second case the fact that \(V_\mu + \ne 0\) implies \(V_{\lambda + (k - \lambda(H_\alpha)) \alpha} = + V_{\sigma_\alpha(\mu)} \ne 0\), which contradicts the fact that \(V_{\lambda + + \ell \alpha} = 0\) for all \(\ell \ge 0\). \end{proof} This is entirely analogous to the situation of \(\mathfrak{sl}_3(K)\), where we @@ -552,9 +553,9 @@ string symmetric with respect to the lines \(K \alpha\) with \(B(\alpha_i - class of arguments leads us to the conclusion\dots \begin{definition} - We refer to the group \(\mathcal{W} = \langle T_\alpha : \alpha \in \Delta^+ - \rangle \subset \operatorname{O}(\mathfrak{h}^*)\) as \emph{the Weyl group of - \(\mathfrak{g}\)}. + We refer to the group \(\mathcal{W} = \langle \sigma_\alpha : \alpha \in + \Delta^+ \rangle \subset \operatorname{O}(\mathfrak{h}^*)\) as \emph{the Weyl + group of \(\mathfrak{g}\)}. \end{definition} \begin{theorem}\label{thm:irr-weight-class}