Vanishing of algebraic Brauer-Manin obstructions

Let X be a homogeneous space of a quasi-trivial k-group G, with geometric stabilizer H, over a number field k. We prove that under certain conditions on the character group of H, certain algebraic Brauer-Manin obstructions to the Hasse principle and weak approximation vanish, because the abelian groups where they take values vanish. When H is connected or abelian, these algebraic Brauer-Manin obstructions to the Hasse principle and weak approximation are the only ones, so we prove the Hasse principle and weak approximation for X under certain conditions. As an application, we obtain new sufficient conditions for the Hasse principle and weak approximation for linear algebraic groups.
Comment: V.5, 13 pages. Following a suggestion of the referee, the proofs of Lemmas 3.2 and 3.4 were omitted in the published version (see V.4). In this version 5, we give detailed proofs of those lemmas