Transformation Groups

, Volume 11, Issue 1, pp 29-49

First online:

The Combinatorics of Category O over symmetrizable Kac-Moody Algebras

  • Peter FiebigAffiliated withMathematisches Institut, Universitat Freiburg, 79104 Freiburg Email author 

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We show that the structure of a block outside the critical hyperplanes of category O over a symmetrizable Kac-Moody algebra depends only on the corresponding integral Weyl group and its action on the parameters of the Verma modules. This is done by giving a combinatorial description of the projective objects in the block. As an application, we derive the Kazhdan-Lusztig conjecture for nonintegral blocks from the integral case for finite or affine Weyl groups. We also prove the uniqueness of Verma embeddings outside the critical hyperplanes.