Motivic Decomposition of Projective Pseudo-Homogeneous Varieties

Abstract

Let G be a semi-simple algebraic group over a field k. Projective G-homogeneous

varieties are projective varieties over which G acts transitively. The stabilizer or the

isotropy subgroup at a point on such a variety is a parabolic subgroup which is always

smooth when the characteristic of k is zero. However, when k has positive characteristic,

we encounter projective varieties with transitive G-action where the isotropy subgroup

need not be smooth. We call these varieties projective pseudo-homogeneous varieties. To every such variety, we can associate a corresponding projective homogeneous variety. In this thesis, we extensively study the Chow motives (with coefficients from a finite connected ring) of projective pseudo-homogeneous varieties for G inner type over k and compare them to the Chow motives of the corresponding projective homogeneous varieties. This is done by proving a generic criterion for the motive of a variety to be isomorphic to the motive of a projective homogeneous variety which works for any characteristic of k. As a corollary, we give some applications and examples of Chow motives that exhibit an interesting phenomenon. We also show that the motives of projective pseudo-homogeneous varieties satisfy properties such as Rost Nilpotence and Krull-Schmidt.