English

Ramified descent

Algebraic Geometry 2026-03-25 v3 Number Theory

Abstract

We investigate the "ramified descent problem": which adelic points of a smooth geometrically connected variety XX defined over a number field KK can be approximated by points that lift to a (twist of a) given ramified cover? We show that the natural descent set corresponding to the problem defines an obstruction to Hasse Principle and weak approximation. Furthermore, we introduce a Brauer-Manin obstruction to the problem. This obstruction can be purely transcendental (and non-trivial) even for abelian covers, which answers in the negative a question posed by Harari at a 2019 workshop. Moreover, the counterexample we produce is also an explicit example of transcendental obstruction to weak approximation for a quotient SLn/GSL_n/G, with GG constant metabelian.

Keywords

Cite

@article{arxiv.2112.00843,
  title  = {Ramified descent},
  author = {Julian Lawrence Demeio},
  journal= {arXiv preprint arXiv:2112.00843},
  year   = {2026}
}
R2 v1 2026-06-24T08:00:34.497Z