Character Sums, Gaussian Hypergeometric Series, and a Family of Hyperelliptic Curves (1507.00914v3)

Abstract: We study the character sums [\phi_{(m,n)}(a,b)=\sum_{x\in\mathbb{F}q}\phi\left(x(x^{m}+a)(x^{n}+b)\right),\textrm{ and, } \psi{(m,n)}(a,b)=\sum_{x\in\mathbb{F}_q}\phi\left((x^{m}+a)(x^{n}+b)\right)] where $\phi$ is the quadratic character defined over $\mathbb{F}_q$. These sums are expressed in terms of Gaussian hypergeometric series over $\mathbb{F}_q$. Then we use these expressions to exhibit the number of $\mathbb{F}_q$-rational points on families of hyperelliptic curves and their Jacobian varieties.