- Commit
- 43d2de9e0550c353493548639a975720bff9cd0f
- Parent
- 2f81acdfc052234279195fd9bb2946e70bc6addf
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Fixed some typos
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Fixed some typos
2 files changed, 19 insertions, 16 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/complete-reducibility.tex | 18 | 10 | 8 |
Modified | sections/introduction.tex | 17 | 9 | 8 |
diff --git a/sections/complete-reducibility.tex b/sections/complete-reducibility.tex @@ -7,9 +7,9 @@ their representations are indeed useful, we are now faced with the Herculean task of trying to understand them. We have seen that representations can be used to derive geometric information about groups, but the question remains: how do we go about classifying the representations of a given Lie algebra? This -is a question that have sparked an entire field of research, and we cannot hope -to provide a comprehensive answer in the \pagedifference{start-47}{end-47} -pages we have left. Nevertheless, we can work on particular cases. +question has sparked an entire field of research, and we cannot hope to provide +a comprehensive answer in the \pagedifference{start-47}{end-47} pages we have +left. Nevertheless, we can work on particular cases. For instance, one can readily check that a \(K^n\)-module \(M\) -- here \(K^n\) denotes the \(n\)-dimensional Abelian Lie algebra -- is nothing more than a @@ -820,7 +820,7 @@ establish\dots 0 \rar & H^1(\mathfrak{g}, M) \rar & 0 \end{tikzcd} \end{center} - then implies \(H^1(\mathfrak{g}, M) = 0\). Hence by induction in \(\dim V\) + then implies \(H^1(\mathfrak{g}, M) = 0\). Hence by induction in \(\dim M\) we find \(H^1(\mathfrak{g}, M) = 0\) for all finite-dimensional \(M\). We are done. \end{proof} @@ -944,10 +944,12 @@ sequence \end{tikzcd} \end{center} -This sequence always splits, which implies we can deduce information about -\(\mathfrak{g}\)-modules by studying the modules of its ``semisimple -part'' \(\mfrac{\mathfrak{g}}{\mathfrak{rad}(\mathfrak{g})}\) -- see -Proposition~\ref{thm:quotients-by-rads}. In practice this translates to\dots +This sequence always splits, which in light of +Example~\ref{ex:all-simple-reps-are-tensor-prod} implies we can deduce +information about \(\mathfrak{g}\)-modules by studying the modules of its +``semisimple part'' \(\mfrac{\mathfrak{g}}{\mathfrak{rad}(\mathfrak{g})}\) -- +see Proposition~\ref{thm:quotients-by-rads}. In practice this translates +to\dots \begin{proposition}[Lie]\label{thm:lie-thm-solvable-reps} Let \(\mathfrak{g}\) be a solvable Lie algebra. Every finite-dimensional
diff --git a/sections/introduction.tex b/sections/introduction.tex @@ -758,7 +758,7 @@ We should stress, however, that the representation theory of Lie algebras is only a small fragment of what is today known as ``representation theory'', which is in general concerned with a diverse spectrum of algebraic and combinatorial structures -- such as groups, quivers and associative algebras. -An introductory exploration of some of this structures can be found in +An introductory exploration of some of these structures can be found in \cite{etingof}. We begin by noting that any \(\mathcal{U}(\mathfrak{g})\)-module \(M\) may be @@ -991,7 +991,10 @@ separate algebras. In particular, we may define\dots \begin{example} Given a Lie algebra \(\mathfrak{g}\), the adjoint \(\mathfrak{g}\)-module is a submodule of the restriction of the adjoint - \(\mathcal{U}(\mathfrak{g})\)-module to \(\mathfrak{g}\). + \(\mathcal{U}(\mathfrak{g})\)-module -- where we consider + \(\mathcal{U}(\mathfrak{g})\) a Lie algebra as in + Example~\ref{ex:inclusion-alg-in-lie-alg}, not as an associative algebra -- + to \(\mathfrak{g}\). \end{example} Surprisingly, this functor has a right adjoint. @@ -1085,9 +1088,7 @@ Example~\ref{ex:tensor-prod-separate-algs} thus provides a way to describe representations of \(\mathfrak{g} \oplus \mathfrak{h}\) in terms of the representations of \(\mathfrak{g}\) and \(\mathfrak{h}\). We will soon see that in many cases \emph{all} (simple) \(\mathfrak{g} \oplus \mathfrak{h}\)-modules -can be constructed in such a manner. - -This concludes our initial remarks on \(\mathfrak{g}\)-modules. In the -following chapters we will explore the fundamental problem of representation -theory: that of classifying all representations of a given algebra up to -isomorphism. +can be constructed in such a manner. This concludes our initial remarks on +\(\mathfrak{g}\)-modules. In the following chapters we will explore the +fundamental problem of representation theory: that of classifying all +representations of a given algebra up to isomorphism.