Crystals via the affine Grassmannian
Abstract
Let $G$ be a connected reductive group over $\CC$ and let $G^{\vee}$ be the Langlands dual group. Crystals for $G^{\vee}$ were introduced by Kashiwara as certain ``combinatorial skeletons'' of finitedimensional representations of $G^{\vee}$. For every dominant integral weight of $G^{\vee}$ Kashiwara constructed a canonical crystal. Other (independent) constructions of those crystals were given by Lusztig and Littelmann. It was also shown by Kashiwara and Joseph that the above family of crystals is unique if certain reasonable conditions are imposed. The purpose of this paper is to give another (rather simple) construction of these crystals using the geometry of the affine Grassmannian $\calG_G=G(\calK)/G(\calO)$ of the group $G$, where $\calK=\CC((t))$ is the field of Laurent power series and $\calO=\CC[[t]]$ is the ring of Taylor series. We check that the crystals we construct satisfy the conditions of the uniqueness theorem mentioned above, which shows that our crystals coincide with those constructed in {\it loc. cit}. It would be interesting to find these isomorphisms directly (cf., however, \cite{Lus3}).
 Publication:

arXiv Mathematics eprints
 Pub Date:
 September 1999
 arXiv:
 arXiv:math/9909077
 Bibcode:
 1999math......9077B
 Keywords:

 Algebraic Geometry;
 Representation Theory
 EPrint:
 10 pages, LaTeX