- Commit
- b4d5b068d6dd2e41769f7486f29e9821958c5e61
- Parent
- dd64c565958db73ddade66f91d07efd19946ba6b
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Made the "1" in "1-dimensional" upwrite
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Made the "1" in "1-dimensional" upwrite
5 files changed, 14 insertions, 14 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/complete-reducibility.tex | 12 | 6 | 6 |
Modified | sections/introduction.tex | 2 | 1 | 1 |
Modified | sections/mathieu.tex | 6 | 3 | 3 |
Modified | sections/semisimple-algebras.tex | 4 | 2 | 2 |
Modified | sections/sl2-sl3.tex | 4 | 2 | 2 |
diff --git a/sections/complete-reducibility.tex b/sections/complete-reducibility.tex @@ -15,9 +15,9 @@ For instance, one can readily check that a representation \(V\) of the \(n\)-dimensional Abelian Lie algebra \(K^n\) is nothing more than a choice of \(n\) commuting operators \(V \to V\) -- corresponding to the action of the canonical basis elements \(e_1, \ldots, e_n \in K^n\). In particular, a -1-dimensional representation of \(K^n\) is just a choice of \(n\) scalars +\(1\)-dimensional representation of \(K^n\) is just a choice of \(n\) scalars \(\lambda_1, \ldots, \lambda_n\). Different choices of scalars yield -non-isomorphic representations, so that the 1-dimensional representations of +non-isomorphic representations, so that the \(1\)-dimensional representations of \(K^n\) are parameterized by points in \(K^n\). This goes to show that classifying the representations of Abelian algebras is @@ -43,7 +43,7 @@ smaller pieces. This leads us to the following definitions. \begin{example} The trivial representation \(K\) is an example of an irreducible - representations. In fact, every 1-dimensional representation \(V\) of a + representations. In fact, every \(1\)-dimensional representation \(V\) of a Lie algebra \(\mathfrak{g}\) is irreducible: \(V\) has no nonzero proper subspaces, let alone \(\mathfrak{g}\)-invariant subspaces. \end{example} @@ -87,7 +87,7 @@ this is not always the case. For instance\dots nonzero proper subrepresentation, which is spanned by the vector \((1, 0)\). This is because if \((a + b, b) = \rho(x) \ (a, b) = \lambda (a, b)\) for some \(\lambda \in K\) then \(\lambda = 1\) and \(b = 0\). Hence \(V\) is - indecomposable -- it cannot be broken into a direct sum of 1-dimensional + indecomposable -- it cannot be broken into a direct sum of \(1\)-dimensional subrepresentations -- but it is evidently not irreducible. \end{example} @@ -706,7 +706,7 @@ establish\dots Since \(\dim W = 2\), the irreducible component \(\mathcal{U}(\mathfrak{g}) \cdot w\) of \(w\) in \(W\) is either \(K w\) or \(W\) itself. But this component cannot be \(W\), since the image the inclusion \(K \to W\) is a - 1-dimensional representation -- i.e. a proper nonzero subrepresentation. + \(1\)-dimensional representation -- i.e. a proper nonzero subrepresentation. Hence \(K w\) is invariant under the action of \(\mathfrak{g}\). In particular, \(X w = 0\) for all \(X \in \mathfrak{g}\). Since \(w\) lies outside the image of the inclusion \(K \to W\), \(\pi(w) \ne 0\) -- which is @@ -910,7 +910,7 @@ proposition~\ref{thm:quotients-by-rads}. In practice this translates to\dots Every irreducible representation of \(\mathfrak{g}\) is the tensor product of an irreducible representation of its semisimple part \(\mfrac{\mathfrak{g}}{\mathfrak{rad}(\mathfrak{g})}\) and a - 1-dimensional representation of \(\mathfrak{g}\). + \(1\)-dimensional representation of \(\mathfrak{g}\). \end{theorem} Having finally reduced our initial classification problem to that of
diff --git a/sections/introduction.tex b/sections/introduction.tex @@ -633,7 +633,7 @@ algebras \(\mathcal{U}(f) : \mathcal{U}(\mathfrak{g}) \to It is important to note, however, that \(\mathcal{U} : K\text{-}\mathbf{LieAlg} \to K\text{-}\mathbf{Alg}\) is not the ``inverse'' of our functor \(K\text{-}\mathbf{Alg} \to K\text{-}\mathbf{LieAlg}\). For instance, if -\(\mathfrak{g} = K\) is the 1-dimensional Abelian Lie algebra then +\(\mathfrak{g} = K\) is the \(1\)-dimensional Abelian Lie algebra then \(\mathcal{U}(\mathfrak{g}) \cong K[x]\), which is infinite-dimensional. Nevertheless, proposition~\ref{thm:universal-env-uni-prop} may be restated as\dots
diff --git a/sections/mathieu.tex b/sections/mathieu.tex @@ -894,7 +894,7 @@ find \(V \subsetneq \mathcal{M}[\lambda]\). In fact, we may find This wasn't an issue an example~\ref{ex:laurent-polynomial-mod} because we verified that the action of \(f \in \mathfrak{sl}_2(K)\) on \(K[x, x^{-1}]\) is -injective. Since all weight spaces of \(K[x, x^{-1}]\) are 1-dimensional, +injective. Since all weight spaces of \(K[x, x^{-1}]\) are \(1\)-dimensional, this implies the action of \(f\) is actually bijective, so we can obtain a nonzero vector in \(K[x, x^{-1}]_{2 k} = K x^k\) for any \(k \in \mathbb{Z}\) by translating between weight spaced using \(f\) and \(f^{-1}\) -- here @@ -1427,7 +1427,7 @@ results. \[ V \cong Z \boxtimes V_1 \boxtimes \cdots \boxtimes V_n \] - where \(Z\) is a 1-dimensional representation of \(\mathfrak{z}\) and \(V_i\) + where \(Z\) is a \(1\)-dimensional representation of \(\mathfrak{z}\) and \(V_i\) is an irreducible weight \(\mathfrak{s}_i\)-module. \end{proposition} @@ -1439,7 +1439,7 @@ results. \end{proposition} We've previously seen that the representations of Abelian Lie algebras, -particularly the 1-dimensional ones, are well understood. Hence to classify the +particularly the \(1\)-dimensional ones, are well understood. Hence to classify the irreducible representations of an arbitrary reductive algebra it suffices to classify those of its simple components. To classify these representations we can apply Fernando's results and reduce the problem to constructing the
diff --git a/sections/semisimple-algebras.tex b/sections/semisimple-algebras.tex @@ -340,7 +340,7 @@ Furthermore, as in the case of \(\mathfrak{sl}_2(K)\) and \(\mathfrak{sl}_3(K)\) one can show\dots \begin{proposition}\label{thm:root-space-dim-1} - The eigenspaces \(\mathfrak{g}_\alpha\) are all 1-dimensional. + The eigenspaces \(\mathfrak{g}_\alpha\) are all \(1\)-dimensional. \end{proposition} The proof of the first statement of @@ -388,7 +388,7 @@ in the case of \(\mathfrak{sl}_3(K)\) we show\dots The proof of proposition~\ref{thm:distinguished-subalgebra} is very technical in nature and we won't include it here, but the idea behind it is simple: recall that \(\mathfrak{g}_\alpha\) and \(\mathfrak{g}_{- \alpha}\) are both -1-dimensional, so that \(\dim [\mathfrak{g}_\alpha, \mathfrak{g}_{- \alpha}]\) +\(1\)-dimensional, so that \(\dim [\mathfrak{g}_\alpha, \mathfrak{g}_{- \alpha}]\) is at most 1. We check that \([\mathfrak{g}_\alpha, \mathfrak{g}_{- \alpha}] \ne 0\) and that no generator of \([\mathfrak{g}_\alpha, \mathfrak{g}_{- \alpha}] \ne 0\) is annihilated by \(\alpha\), so that by adjusting scalars we
diff --git a/sections/sl2-sl3.tex b/sections/sl2-sl3.tex @@ -139,7 +139,7 @@ self-evident: we have just provided a complete description of the action of \(\mathfrak{sl}_2(K)\) on \(V\). In particular, this goes to show\dots \begin{corollary} - Every eigenspace of the action of \(h\) on \(V\) is 1-dimensional. + Every eigenspace of the action of \(h\) on \(V\) is \(1\)-dimensional. \end{corollary} \begin{proof} @@ -217,7 +217,7 @@ Surprisingly, we have already encountered such a \(V\). Either way, by the previous observation that a finite-dimensional representation whose eigenvalues all have the same parity and whose - corresponding eigenspace are all 1-dimensional must be irreducible, \(V\) is + corresponding eigenspace are all \(1\)-dimensional must be irreducible, \(V\) is irreducible. As for the uniqueness of \(V\), it suffices to notice that if \(W\) is a finite-dimensional irreducible representation of \(\mathfrak{sl}_2(K)\) with right-most eigenvector \(w\) then relations