- Commit
- d420135863e0d433367ec53178d01c15a4ea460b
- Parent
- 1fce6426365d6b979283f3c82096829b9cff4b4f
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Fixed typos and removed unnecessary whitespace
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Fixed typos and removed unnecessary whitespace
1 file changed, 10 insertions, 10 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/semisimple-algebras.tex | 20 | 10 | 10 |
diff --git a/sections/semisimple-algebras.tex b/sections/semisimple-algebras.tex @@ -156,10 +156,10 @@ come in handy later on, is the following. the \(\mathfrak{g}\)-invariant bilinear form \begin{align*} B_V : \mathfrak{g} \times \mathfrak{g} & \to K \\ - (X, Y) & + (X, Y) & \mapsto \operatorname{Tr}(X\!\restriction_V \circ Y\!\restriction_V) \end{align*} - is non-degenerate\footnote{A simmetric bilinear form $B : \mathfrak{g} + is non-degenerate\footnote{A symmetric bilinear form $B : \mathfrak{g} \times \mathfrak{g} \to K$ is called non-degenerate if $B(X, Y) = 0$ for all $Y \in \mathfrak{g}$ implies $X = 0$.}. \item The Killing form \(B\) is non-degenerate. @@ -1888,13 +1888,13 @@ What is simultaneous diagonalization all about then? We should point out that simultaneous diagonalization \emph{only works in the finite-dimensional setting}. In fact, simultaneous diagonalization is usually framed as an equivalent statement about diagonalizable \(n \times n\) matrices --- where \(n\) is, of course, finite. +-- where \(n\) is, of course, finite. Simultaneous diagonalization implies that to show \(V = \bigoplus_\lambda V_\lambda\) it suffices to show that \(H\!\restriction_V : V \to V\) is a diagonalizable operator for each \(H \in \mathfrak{h}\). To that end, we introduce \emph{the Jordan decomposition of an operator} and \emph{the abstract -Jorden decomposition of a semisimple Lie algebra}. +Jordan decomposition of a semisimple Lie algebra}. \begin{proposition}[Jordan] Given a finite-dimensional vector space \(V\) and an operator \(T : V \to @@ -1912,7 +1912,7 @@ Jorden decomposition of a semisimple Lie algebra}. is known as \emph{the Jordan decomposition of \(X\)}. \end{proposition} -It should be clear from the uniqueless of \(\operatorname{ad}(X)_s\) and +It should be clear from the uniqueness of \(\operatorname{ad}(X)_s\) and \(\operatorname{ad}(X)_n\) that the Jordan decomposition of \(\operatorname{ad}(X)\) is \(\operatorname{ad}(X) = \operatorname{ad}(X_s) + \operatorname{ad}(X_n)\). What's perhaps more remarkable is the fact this holds @@ -1928,9 +1928,9 @@ words\dots This last result is known as \emph{the preservation of the Jordan form}, and a proof can be found in appendix C of \cite{fulton-harris}. We should point out -this fails spetacularly in positive characteristic. Furtheremore, the statement -of proposition~\ref{thm:preservation-jordan-form} only makes sence for -\emph{semisimple} Lie algebras -- i.e. the algebras \(\mathfrak{g}\) for wich +this fails spectacularly in positive characteristic. Furthermore, the statement +of proposition~\ref{thm:preservation-jordan-form} only makes sense for +\emph{semisimple} Lie algebras -- i.e. the algebras \(\mathfrak{g}\) for which the abstract Jordan decomposition of \(\mathfrak{g}\) is defined. Nevertheless, as promised this implies\dots @@ -1953,7 +1953,7 @@ as promised this implies\dots \begin{proof} Fix some \(H \in \mathfrak{h}\). It suffices to show that \(H\!\restriction_V - : V \to V\) is a diagonalizable operator. + : V \to V\) is a diagonalizable operator. If we write \(H = H_s + H_n\) for the abstract Jordan decomposition of \(H\), we know \(\operatorname{ad}(H_s) = \operatorname{ad}(H)_s\). But @@ -1967,7 +1967,7 @@ as promised this implies\dots \end{proof} We should point out that this last proof only works for semisimple Lie -algebras. This is because we rely heavely on +algebras. This is because we rely heavily on proposition~\ref{thm:preservation-jordan-form}, as well in the fact that semisimple Lie algebras are centerless. In fact, corollary~\ref{thm:finite-dim-is-weight-mod} fails even for reductive Lie