Linear Combinations of Logarithms of $L$-functions over Function Fields at Microscopic Shifts and Beyond

Abstract

In the function field setting with a fixed characteristic, it was proven by the second and third authors that the values $\log \big|L\big(\frac12, χ_D\big)\big|$ as $D$ varies over monic and square-free polynomials are asymptotically Gaussian distributed on the assumption of a low lying zeros hypothesis as the degree of $D$ tends to $\infty$. For real distinct shifts $t_j$ all of microscopic size or all of nonmicroscopic size relative to the genus, we consider linear combinations of $\log\big|L\big(\frac12+it_j, χ_D\big)\big|$ with real coefficients, and separately, of $\arg L\big(\frac12+it_j, χ_D\big).$ We provide estimates for their distribution functions under the low lying zeros hypothesis. We similarly study distribution functions of linear combinations of $\log\big|L\big(\frac12+it_j, E\otimes χ_D\big)\big|$, and separately $\arg L\big(\frac12+it_j, E\otimesχ_D\big)$, for quadratic twists of elliptic curves $E$ with root number one as the conductor gets large. As an application of these results, we prove a central limit theorem for the fluctuation of the number of nontrivial zeros of such $L$-functions from its mean, and thus recover previous results by Faifman and Rudnick. Correlations of such fluctuations are in harmony with the results of Bourgade, Coram and Diaconis, and Wieand for zeros of the Riemann zeta function and for eigenangles of unitary random matrices.