Gluing of perverse sheaves on the basic affine space

Abstract

This paper is devoted to the study of the gluing construction for perverse sheaves on $G/U$ introduced by Kazhdan and Laumon ($G$ is a semisimple gourp, $U$ is the unipotent radical of a Borel subgroup in $G$). Kazhdan and Laumon conjectured that all Ext-groups in the glued category are finite-dimensional and that global cohomological dimension is finite. We prove the first part of this conjecture. In the appendix we show that the simple object in the glued category corresponding to the constant sheaf has infinite cohomological dimension, thus disproving the second part of the above conjecture.