English

Squares in $\mathbb{F}_{p^2}$ and permutations involving primitive roots

Number Theory 2020-02-05 v2

Abstract

Let p=2n+1p=2n+1 be an odd prime, and let ζp21\zeta_{p^2-1} be a primitive (p21)(p^2-1)-th root of unity in the algebraic closure Qp\overline{\mathbb{Q}_p} of Qp\mathbb{Q}_p. We let gZp[ζp21]g\in\mathbb{Z}_p[\zeta_{p^2-1}] be a primitive root modulo pZp[ζp21]p\mathbb{Z}_p[\zeta_{p^2-1}] with gζp21(modpZp[ζp21])g\equiv \zeta_{p^2-1}\pmod {p\mathbb{Z}_p[\zeta_{p^2-1}]}. Let Δ3(mod4)\Delta\equiv3\pmod4 be an arbitrary quadratic non-residue modulo pp in Z\mathbb{Z}. By the Local Existence Theorem we know that Qp(Δ)=Qp(ζp21)\mathbb{Q}_p(\sqrt{\Delta})=\mathbb{Q}_p(\zeta_{p^2-1}). For all xZ[Δ]x\in\mathbb{Z}[\sqrt{\Delta}] and yZp[ζp21]y\in\mathbb{Z}_p[\zeta_{p^2-1}] we use xˉ\bar{x} and yˉ\bar{y} to denote the elements xmodpZ[Δ]x\mod p\mathbb{Z}[\sqrt{\Delta}] and ymodpZp[ζp21]y\mod p\mathbb{Z}_p[\zeta_{p^2-1}] respectively. If we set ak=k+Δa_k=k+\sqrt{\Delta} for 0kp10\le k\le p-1, then we can view the sequence S:=a02,,a02n2,,ap12,,ap12n2,12,,n2S := \overline{a_0^2}, \cdots, \overline{a_0^2n^2}, \cdots,\overline{a_{p-1}^2}, \cdots, \overline{a_{p-1}^2n^2}\cdots, \overline{1^2}, \cdots,\overline{n^2} as a permutation σ\sigma of the sequence S:=g2,g4,,gp21.S^* := \overline{g^2}, \overline{g^4}, \cdots,\overline{g^{p^2-1}}. We determine the sign of σ\sigma completely in this paper.

Keywords

Cite

@article{arxiv.1908.07641,
  title  = {Squares in $\mathbb{F}_{p^2}$ and permutations involving primitive roots},
  author = {Hai-Liang Wu},
  journal= {arXiv preprint arXiv:1908.07641},
  year   = {2020}
}
R2 v1 2026-06-23T10:52:45.655Z