English

On tamely ramified infinite Galois extensions

Number Theory 2024-01-15 v2

Abstract

For a number field KK, we consider KtaK^{\rm ta} the maximal tamely ramified algebraic extension of~KK, and its Galois group GKta=Gal(Kta/K)G^{\rm ta}_K= Gal(K^{ta}/K). Choose a prime pp such that μp⊄K\mu_p \not \subset K. Our guiding aim is to characterize the finitely generated pro-pp quotients of~GtaG^{\rm ta}. We give a {unified point of view} by introducing the notion of {\it stably inertially generated} pro-pp groups~GG, for which linear groups are archetypes. This key notion {is compatible} with local {\it tame liftings} as used in the Scholz-Reichardt Theorem. We realize every finitely generated pro-pp group~GG which is stably inertially generated as a quotient of GtaG^{\rm ta}. Further examples of groups that we realize as quotients of GtaG^{\rm ta} include congruence subgroups of special linear groups over Zp[[T1,,Tn]]{\mathbb Z}_p[[ T_1,\cdots, T_n ]]. Finally, we give classes of groups which cannot be realized as quotients of GQtaG^{\rm ta}_{\mathbb Q}.

Keywords

Cite

@article{arxiv.2401.05927,
  title  = {On tamely ramified infinite Galois extensions},
  author = {Farshid Hajir and Michael Larsen and Christian Maire and Ravi Ramakrishna},
  journal= {arXiv preprint arXiv:2401.05927},
  year   = {2024}
}