We introduce an Uhlenbeck closure of the space of based maps from projective line to the Kashiwara ﬂag scheme of an untwisted affine Lie algebra. For the algebra sln this space of based maps is isomorphic to the moduli space of locally free parabolic sheaves on _P_1 × _P_1 trivialized at inﬁnity. The Uhlenbeck closure admits a resolution of singularities: the moduli space of torsion free parabolic sheaves on _P_1 × _P_1 trivialized at inﬁnity. We compute the Intersection Cohomology sheaf of the Uhlenbeck space using this resolution of singularities. The moduli spaces of parabolic sheaves of various degrees are connected by certain Hecke correspondences. We prove that these correspondences deﬁne an action of sln in the cohomology of the above moduli spaces.
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Michael Finkelberg, Dennis Gaitsgory, Alexander Kuznetsov, Uhlenbeck Spaces for <strong>A</strong><sup>2</sup> and Affine Lie Algebra <span style="text-decoration: overline;"><strong>sl</strong></span><sub><em>n</em></sub>. Publ. Res. Inst. Math. Sci. 39 (2003), no. 4, pp. 721–766DOI 10.2977/PRIMS/1145476045