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


Abstract in English

Let $p=2n+1$ be an odd prime, and let $zeta_{p^2-1}$ be a primitive $(p^2-1)$-th root of unity in the algebraic closure $overline{mathbb{Q}_p}$ of $mathbb{Q}_p$. We let $ginmathbb{Z}_p[zeta_{p^2-1}]$ be a primitive root modulo $pmathbb{Z}_p[zeta_{p^2-1}]$ with $gequiv zeta_{p^2-1}pmod {pmathbb{Z}_p[zeta_{p^2-1}]}$. Let $Deltaequiv3pmod4$ be an arbitrary quadratic non-residue modulo $p$ in $mathbb{Z}$. By the Local Existence Theorem we know that $mathbb{Q}_p(sqrt{Delta})=mathbb{Q}_p(zeta_{p^2-1})$. For all $xinmathbb{Z}[sqrt{Delta}]$ and $yinmathbb{Z}_p[zeta_{p^2-1}]$ we use $bar{x}$ and $bar{y}$ to denote the elements $xmod pmathbb{Z}[sqrt{Delta}]$ and $ymod pmathbb{Z}_p[zeta_{p^2-1}]$ respectively. If we set $a_k=k+sqrt{Delta}$ for $0le kle p-1$, then we can view the sequence $$S := overline{a_0^2}, cdots, overline{a_0^2n^2}, cdots,overline{a_{p-1}^2}, cdots, overline{a_{p-1}^2n^2}cdots, overline{1^2}, cdots,overline{n^2}$$ as a permutation $sigma$ of the sequence $$S^* := overline{g^2}, overline{g^4}, cdots,overline{g^{p^2-1}}.$$ We determine the sign of $sigma$ completely in this paper.

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