Co-$t$-structures on derived categories of coherent sheaves and the cohomology of tilting modules

Pramod N. Achar, William Hardesty

Published 2020-12-11, updated 2022-03-22Version 2

We construct a co-$t$-structure on the derived category of coherent sheaves on the nilpotent cone $\mathcal{N}$ of a reductive group, as well as on the derived category of coherent sheaves on any parabolic Springer resolution. These structures are employed to show that the push-forwards of the "exotic parity objects" along the (classical) Springer resolution give indecomposable objects inside the coheart of the co-$t$-structure on $\mathcal{N}$. We also demonstrate how the various parabolic co-$t$-structures can be related by introducing an analogue to the usual translation functors. As an application, we give a proof of a scheme-theoretic formulation of the relative Humphreys conjecture on support varieties of tilting modules in type $A$ for $p>h$.