English

Description of the strong approximation locus using Brauer-Manin obstruction for homogeneous spaces with commutative stabilizers

Algebraic Geometry 2025-08-29 v1 Number Theory

Abstract

For a homogeneous space XX over a number field kk, the Brauer-Manin obstruction has been used to study strong approximation for XX away from a finite set SS of places, and known results state that X(k)X(k) is dense in the omitting-SS projection of the Brauer-Manin set prS(X(Ak)br)\mathrm{pr}_S(X(\mathbb{A}_k)^{\mathrm{br}}), under certain assumptions. In order to completely understand the closure of X(k)X(k) in the set of SS-adelic points X(AkS)X(\mathbb{A}_k^S), we ask: (i) whether prS(X(Ak)br)\mathrm{pr}_S(X(\mathbb{A}_k)^{\mathrm{br}}) is closed in X(AkS)X(\mathbb{A}_k^S); (ii) whether X(k)X(k) is dense in the closed subset of X(AkS)X(\mathbb{A}_k^S) cut out by elements in brX\mathrm{br}X which induce zero evaluation maps at all the places in SS. We also ask these questions considering only the algebraic Brauer group. We give answers to such questions for homogeneous spaces XX under semisimple simply connected groups with commutative stabilizers.

Keywords

Cite

@article{arxiv.2508.20652,
  title  = {Description of the strong approximation locus using Brauer-Manin obstruction for homogeneous spaces with commutative stabilizers},
  author = {Victor de Vries and Haowen Zhang},
  journal= {arXiv preprint arXiv:2508.20652},
  year   = {2025}
}

Comments

28 pages, comments welcome!