We prove the Mirković–Vilonen conjecture: the integral local intersection cohomology groups of spherical Schubert varieties on the affine Grassmannian have no$p$-torsion, as long as$p$is outside a certain small and explicitly given set of prime numbers. (Juteau has exhibited counterexamples when$p$is a bad prime.) The main idea is to convert this topological question into an algebraic question about perverse-coherent sheaves on the dual nilpotent cone using the Juteau–Mautner–Williamson theory of parity sheaves.

Let$M$be a compact complex manifold. The corresponding Teichmüller space Teich is the space of all complex structures on$M$up to the action of the group $${{\rm Diff}_0(M)}$$ of isotopies. The mapping class group $${\Gamma:={\rm Diff}(M)/{{\rm Diff}_0(M)}}$$ acts on Teich in a natural way. An$ergodic complex structure$is a complex structure with a $${\Gamma}$$ -orbit dense in Teich. Let$M$be a complex torus of complex dimension $${\ge 2}$$ or a hyperkähler manifold with $${b_2 > 3}$$ . We prove that$M$is ergodic, unless$M$has maximal Picard rank (there are countably many such$M$). This is used to show that all hyperkähler manifolds are Kobayashi non-hyperbolic.

We study mixing properties of commutative groups of automorphisms acting on compact nilmanifolds. Assuming that every non-trivial element acts ergodically, we prove that such actions are mixing of all orders. We further show exponential 2-mixing and 3-mixing. As an application we prove smooth cocycle rigidity for higher-rank abelian groups of nilmanifold automorphisms.