On the distribution of the rational points on cyclic covers in the absence of roots of unity

Abstract: In this paper we study the number of rational points on curves in an ensemble of abelian covers of the projective line: Let $\ell$ be a prime, $q$ a prime power and consider the ensemble $\mathcal{H}{g,\ell}$ of $\ell$-cyclic covers of $\mathbb{P}^1{\mathbb{F}q}$ of genus $g$. We assume that $q\not\equiv 0,1\mod \ell$. If $2g+2\ell-2\not\equiv0\mod (\ell-1){\rm ord}\ell(q)$, then $\mathcal{H}{g,\ell}$ is empty. Otherwise, the number of rational points on a random curve in $\mathcal{H}{g,\ell}$ distributes as $\sum_{i=1}^{q+1} X_i$ as $g\to \infty$, where $X_1,\ldots, X_{q+1}$ are i.i.d.\ random variables taking the values $0$ and $\ell$ with probabilities $\frac{\ell-1}{\ell}$ and $\frac{1}{\ell}$, respectively. The novelty of our result is that it works in the absence of a primitive $\ell$-th-root of unity, the presence of which was crucial in previous studies.