- Commit
- 58d706bd4a0d1af29dd7a3356f119ab9126db850
- Parent
- 369f54cbbbc2419b55d20f5d09f1afc1e928675b
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Rewrote the introduction of the chapter on sl2 and sl3
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Rewrote the introduction of the chapter on sl2 and sl3
2 files changed, 19 insertions, 18 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/complete-reducibility.tex | 4 | 2 | 2 |
Modified | sections/sl2-sl3.tex | 33 | 17 | 16 |
diff --git a/sections/complete-reducibility.tex b/sections/complete-reducibility.tex @@ -901,5 +901,5 @@ Having finally reduced our initial classification problem to that of classifying the finite-dimensional irreducible representations of \(\mathfrak{g}\), we can now focus exclusively in irreducible \(\mathfrak{g}\)-modules. However, there is so far no indication on how we -could go about understanding them. In the next chapter we'll explore concrete -examples in the hopes of finding a solution to our general problem. +could go about understanding them. In the next chapter we'll explore some +concrete examples in the hopes of finding a solution to our general problem.
diff --git a/sections/sl2-sl3.tex b/sections/sl2-sl3.tex @@ -1,17 +1,19 @@ \chapter{Low-Dimensional Examples}\label{ch:sl3} -% TODOOOO: Write an intetroduction! - -The primary goal of this section is proving\dots - -\begin{theorem}\label{thm:sl2-exist-unique} - For each \(n > 0\), there exists precisely one irreducible representation - \(V\) of \(\mathfrak{sl}_2(K)\) with \(\dim V = n\). -\end{theorem} - -The general approach we'll take is supposing \(V\) is an irreducible -representation of \(\mathfrak{sl}_2(K)\) and then derive some information about -its structure. We begin our analysis by recalling that the elements +We are, once again, faced with the daunting task of classifying the +finite-dimensional representations of a given (semisimple) algebra +\(\mathfrak{g}\). Having reduced the problem a great deal, all its left is +classifying the irreducible representations of \(\mathfrak{g}\). +We've encountered numerous examples of irreducible \(\mathfrak{g}\)-modules +over the previous chapter, but we have yet to subject them to any serious +scrutiny. In this chapter we begin a sistematic investigation of +irreducible representations by looking at concrete examples. +Specifically, we'll classify the irreducible finite-dimensional representations +of certain low-dimensional semisimple Lie algebras. + +Throughout the previous chapters \(\mathfrak{sl}_2(K)\) has afforded us +surprisingly elucidative examples, so it will serve as our first canditate for +low-dimensional algebra. We begin our analysis by recalling that the elements \begin{align*} e & = \begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix} & f & = \begin{pmatrix} 0 & 0 \\ 1 & 0 \end{pmatrix} & @@ -22,9 +24,8 @@ form a basis of \(\mathfrak{sl}_2(K)\) and satisfy [e, f] & = h & [h, f] & = -2 f & [h, e] = 2 e \end{align*} -This is interesting to us because it implies every subspace of \(V\) invariant -under the actions of \(e\), \(f\) and \(h\) has to be \(V\) itself. Next we -turn our attention to the action of \(h\) in \(V\), in particular, to the +Let \(V\) be a finite-dimensional irreducible \(\mathfrak{sl}_2(K)\)-module. We +now turn our attention to the action of \(h\) in \(V\), in particular, to the eigenspace decomposition \[ V = \bigoplus_{\lambda} V_\lambda @@ -938,7 +939,7 @@ Finally\dots Having found all of the weights of \(V\), the only thing we're missing is an existence and uniqueness theorem analogous to -theorem~\ref{thm:sl2-exist-unique}. In other words, our next goal is +theorem~\ref{thm:irr-rep-of-sl2-exists}. In other words, our next goal is establishing\dots \begin{theorem}\label{thm:sl3-existence-uniqueness}