Reconstructing decomposition subgroups in arithmetic fundamental groups using regulators

Abstract

Our main goal in the present article is to explain how one can reconstruct the decomposition subgroups and norms of points on an arithmetic curve inside its fundamental group if the following data are given: the fundamental group, a part of the cyclotomic character and the family of the regulators of the fields corresponding to the generic points of all \'{e}tale covers of the given curve. The approach is inspired by that of Tamagawa for curves over finite fields but uses Tsfasman-Vl\u{a}du\c{t} theorem instead of Lefschetz trace formula. To the authors' knowledge, this is a new technique in the anabelian geometry of arithmetic curves. It is conditional and depends on still unknown properties of arithmetic fundamental groups. We also give a new approach via Iwasawa theory to the local correspondence at the boundary.Comment: 17 pages; this is a second version of the article. Certain significant changes were made. The two most important are: a section on local correspondence on the boundary via Greenberg conjecture in Iwasawa theory was added and, following a suggestion of a referee, the conditions in the main theorem were weakene