English

Lifting Galois representations via Kummer flags

Number Theory 2026-03-02 v5 Algebraic Topology

Abstract

Let Γ\Gamma be either i) the absolute Galois group of a local field FF, or ii) the topological fundamental group of a closed connected orientable surface of genus gg. In case i), assume that μp2F\mu_{p^2} \subset F. We give an elementary and unified proof that every representation ρ1:ΓGLd(Fp)\rho_1: \Gamma \to \mathbf{GL}_d(\mathbb{F}_p) lifts to a representation ρ2:ΓGLd(Z/p2)\rho_2: \Gamma \to \mathbf{GL}_d(\mathbb{Z}/p^2). [In case i), it is understood these are continuous.] The actual statement is much stronger: for all r1r \geq 1, under "suitable" assumptions, triangular representations ρr:ΓBd(Z/pr)\rho_r: \Gamma \to \mathbf{B}_d(\mathbb{Z}/p^r) lift to ρr+1:ΓBd(Z/pr+1)\rho_{r+1}: \Gamma \to \mathbf{B}_d(\mathbb{Z}/p^{r+1}), in the strongest possible step-by-step sense. Here "suitable" is made precise by the concept of Kummer flag\textit{Kummer flag}. An essential aspect of this work is to identify the common properties of groups i) and ii) that suffice to ensure the existence of such lifts.

Keywords

Cite

@article{arxiv.2403.08888,
  title  = {Lifting Galois representations via Kummer flags},
  author = {Andrea Conti and Cyril Demarche and Mathieu Florence},
  journal= {arXiv preprint arXiv:2403.08888},
  year   = {2026}
}

Comments

29 pages. We fixed a problem in the last case of the proof of Theorem 7.21

R2 v1 2026-06-28T15:19:17.968Z