Traces of High Powers of the Frobenius Class in the Moduli Space of Hyperelliptic Curves

Abstract

The Zeta function of a curve $C$ over a finite field may be expressed in terms of the characteristic polynomial of a unitary matrix $\Theta_C$. Following the work of Rudnick, we compute the expected value of $\mbox{tr}(\Theta_C^n)$ over the moduli space of hyperelliptic curves of genus $g$, over a fixed finite field $\mathbb{F}_q$, in the limit of large genus. As an application, we compute the expected value of the number of points on $C$ in $\mathbb{F}_{q^n}$ as the genus tends to infinity. We also look at biases in both expected values for small values of $n$.