English

Lifting Galois sections along torsors

Algebraic Geometry 2015-08-18 v2 Number Theory

Abstract

The cuspidalization conjecture, which is a consequence of Grothendieck's section conjecture, asserts that for any smooth hyperbolic curve XX over a finitely generated field kk of characteristic 00 and any non empty Zariski open UXU \subset X, every section of π1(X,xˉ)Galk\pi _1 (X, \bar x) \to \mathrm{Gal}_k lifts to a section of π1(U,xˉ)Galk\pi _1 (U,\bar x) \to \mathrm{Gal}_k. We consider in this article the problem of lifting Galois sections to the intermediate quotient π1cc(U) \pi_1^{cc}(U) introduced by Mochizuki. We show that when k=Qk = \mathbb Q and D=XUD=X\setminus U is an union of torsion sub-packets every Galois section actually lifts to π1cc(U) \pi_1^{cc}(U). One of the main tools in the proof is the construction of torus torsors FDF_D and EDE_D over XX and the geometric interpretation π1cc(U)π1(FD) \pi_1^{cc}(U) \simeq \pi _1 (F_D).

Keywords

Cite

@article{arxiv.1301.4429,
  title  = {Lifting Galois sections along torsors},
  author = {Niels Borne and Michel Emsalem and Jakob Stix},
  journal= {arXiv preprint arXiv:1301.4429},
  year   = {2015}
}

Comments

v2 corresponds to the published, deeply revised and much shortened version. We think that v1, that contains the same results, could still be helpful to the reader preferring a self-contained text

R2 v1 2026-06-21T23:11:52.745Z