Reducible good representations of semisimple Lie algebras $A_r$ and $B_r$ Part I
Given a semisimple (preferably simple) complex Lie algebra $L$, we consider the monoid $\Gamma=\Gamma(L)$ of equivalence classes of the finite dimensional reducible complex representations of $L$. Here $\Gamma$ is identified with the lattice of the corresponding highest weights. (This equips $\Gamma$ with the monoid structure.) For $\pi\in\Gamma$ one considers the symmetric algebra $\displaystyle S(\pi)=\bigoplus_{n=0}^{\infty}S^n(\pi)$ (here regarded as a representation). The elements of $\Gamma$ ``occurring'' in $S(\pi)$ -- i.e., which are the highest weights of some irreducible component of the representation $S(\pi)$ -- form a subsemigroup $M(\pi)$ of $\Gamma$. Such a $M(\pi)$ has a naturally defined rank $r(\pi)$ with $1\leq r(\pi)\leq r = \text{rank of }L$. In this paper we give a classification, for all the simple $L=A_r$ and $L=B_r$ of all the $\pi$ with $r(\pi)< r$.
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- [1] A.G. Elashvili, Canonical form and stationary subalgebras of points of general position
for simple linear Lie groups, Funct. Anal. Appl. 6, 44–53, 1972.
- [2] R. Güner, Klassifikation gewisser Darstellungen halbeinfacher Liealgebren, https://epub.uni-bayreuth.de/347/1/3.Diss.pdf.pdf.
- [3] W.-Chung Hsiang and W.-Yi Hsiang, Differential actions of compact connected classical
groups: II, Ann. of Math. (2), 91–92, 1970.
- [4] J.E. Humphreys, Introduction to Lie Algebras and Representation Theory, Springer-
Verlag, New York-Heidelberg-Berlin, 1972.
- [5] M. Krämer, Hauptisotropiegruppen bei endlichen dimensionalen Darstellungen kompakter
halbeinfacher Liegruppen, Diplomarbeit, Bonn, 1966.
- [6] M. Krämer, Über Untergruppen kompakter Liegruppen als Isotropiegruppen bei linearen
Aktionen, Math. Z. 147, 207–224, 1976.
- [7] D.I. Panyushev, Complexity and rank of homegeneous spaces, Geom. Dedicata, 34,
249–269, 1990.
- [8] J. Tits, Tabellen zu den einfachen Lie Gruppen und ihren Darstellungen, Lecture Notes
in Mathematics No. 40, Berlin-Heidelberg-New York, Springer, 1967.
- [9] M.A.A. Van Leeuwen, A.M. Cohen and B. Lisser, A package for Lie group computations,
Can., Amsterdam 1992.