Perverse sheaves and t-structures on the thin and thick affine flag varieties

Roman Bezrukavnikov, Calder Morton-Ferguson

Published 2024-09-24Version 1

We study the categories $\mathrm{Perv}_{\mathrm{thin}}$ and $\mathrm{Perv}_{\mathrm{thick}}$ of Iwahori-equivariant perverse sheaves on the thin and thick affine flag varieties associated to a split reductive group $G$. An earlier work of the first author describes $\mathrm{Perv}_{\mathrm{thin}}$ in terms of bimodules over the so-called non-commutative Springer resolution. We partly extend this result to $\mathrm{Perv}_{\mathrm{thick}}$, providing a similar description for its anti-spherical quotient. The long intertwining functor realizes $\mathrm{Perv}_{\mathrm{thick}}$ as the Ringel dual of $\mathrm{Perv}_{\mathrm{thin}}$, we point out that it shares some exactness properties with the similar functor acting on perverse sheaves on the finite-dimensional flag variety. We use this result to resolve a conjecture of Arkhipov and the first author, proving that the image in the Iwahori-Whittaker category of any convolution-exact perverse sheaf on the affine flag variety is tilting.