English

Arithmetic descent of specializations of Galois covers

Algebraic Geometry 2023-09-22 v4 Number Theory

Abstract

Given a GG-Galois branched cover of the projective line over a number field KK, we study whether there exists a closed point of PK1\mathbb{P}^1_K with a connected fiber such that the GG-Galois field extension induced by specialization "arithmetically descends" to Q\mathbb{Q} (i.e., there exists a GG-Galois field extension of Q\mathbb{Q} whose compositum with the residue field of the point is equal to the specialization). We prove that the answer is frequently positive (whenever GG is regularly realizable over Q\mathbb{Q}) if one first allows a base change to a finite extension of KK. If one does not allow base change, we prove that the answer is positive when GG is cyclic. Furthermore, we provide an explicit example of a Galois branched cover of PK1\mathbb{P}^1_K with no KK-rational points of arithmetic descent.

Keywords

Cite

@article{arxiv.1412.1682,
  title  = {Arithmetic descent of specializations of Galois covers},
  author = {Ryan Eberhart and Hilaf Hasson},
  journal= {arXiv preprint arXiv:1412.1682},
  year   = {2023}
}

Comments

Fixed a typo in the last paragraph of Section 1