Foliations in deformation spaces of local G-shtukas

We study local G-shtukas with level structure over a base scheme whose Newton polygons are constant on the base. We show that after a finite base change and after passing to an étale covering, such a local G-shtuka is isogenous to a completely slope divisible one, generalizing corresponding results for p-divisible groups by Oort and Zink. As an application we establish a product structure up to finite surjective morphism on the closed Newton stratum of the universal deformation of a local G-shtuka, similarly to Oortʼs foliations for p-divisible groups and abelian varieties. This also yields bounds on the dimensions of affine Deligne–Lusztig varieties and proves equidimensionality of affine Deligne–Lusztig varieties in the affine Grassmannian.