English

Twists arising from torsion points

Number Theory 2025-10-10 v1

Abstract

Let pp be a prime number, KK a number field that contains the pp-th root of unity ζp\zeta_p, dd a pp-power-free integer and L=K(dp)L=K(\sqrt[p]{d}). Let E/KE/K be an elliptic curve with full pp-torsion and S,TE(K)[p]S,T \in E(K)[p] be the generators. Define the cocycle ξd:Gal(K/K)E\xi_d : \operatorname{Gal}(\overline{K}/K) \to E by ξd(σ)={O,if σ(dp)=dp,kS,if σ(dp)=ζpkdp, \xi_d (\sigma)= \begin{cases} O, & \text{if } \sigma(\sqrt[p]{d})=\sqrt[p]{d}, \newline kS, & \text{if } \sigma(\sqrt[p]{d})=\zeta_p^k\sqrt[p]{d}, \end{cases} and denote by HSdH_S^d the twist of EE corresponding to the cocycle ξd\xi_d. In this paper we construct generators zz and ww of the function field K(HSd)K(H_S^d) and give a model of the twist HSd:α1zp+α2zp2w++αp+12zwp12+βwp+γ=0. H_S^d\,:\, \alpha_{1}z^p+\alpha_2z^{p-2}w+\dotso+\alpha_{\frac{p+1}{2}}zw^{\frac{p-1}{2}}+\beta w^p+\gamma=0. We also obtain that the twist HSdH_S^d is everywhere locally solvable only for finitely many integers dd.

Keywords

Cite

@article{arxiv.2510.08486,
  title  = {Twists arising from torsion points},
  author = {Lukas Novak},
  journal= {arXiv preprint arXiv:2510.08486},
  year   = {2025}
}

Comments

10 pages; comments welcome

R2 v1 2026-07-01T06:27:26.006Z