A finite-dimensional irreducible representation of a complex semisimple Lie algebra is minuscule if its weights form one Weyl group orbit. Every weight multiplicity is then one, because multiplicities are invariant under the Weyl group and the highest weight has multiplicity one.
The formal character of a weight module for a minuscule representation of highest weight is . The sum is over distinct points of the Weyl group orbit, so .
A dominant integral weight is minuscule when its irreducible highest-weight representation is a minuscule representation. Equivalently, for every positive root . This convention includes the zero weight and its trivial Lie algebra representation.
By dominant root-lattice highest weights have zero weight, a minuscule weight in the root lattice has zero in its Weyl group orbit. Since every element of the Weyl group is invertible, the highest weight must itself be zero. Thus equality of the weight lattice and root lattice rules out every nontrivial minuscule representation without requiring a classification of root systems.
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Minuscule representation is a term often used in various contexts, including typography, linguistics, and even in some musical notation or computer science. However, its most common reference is in the field of linguistics and typography, where "minuscule" typically refers to lowercase letters as opposed to uppercase (capital) letters.