Ramified descent
Abstract
We investigate the "ramified descent problem": which adelic points of a smooth geometrically connected variety defined over a number field 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 , with constant metabelian.
Cite
@article{arxiv.2112.00843,
title = {Ramified descent},
author = {Julian Lawrence Demeio},
journal= {arXiv preprint arXiv:2112.00843},
year = {2026}
}