A quadratic divisor problem and moments of the Riemann zeta-function

TL;DR

This paper provides an asymptotic estimate for the fourth moment of the Riemann zeta-function twisted by a Dirichlet polynomial, extending previous results and utilizing Watt's theorem to improve understanding of zeros and moments.

Contribution

It introduces an asymptotic formula for a quadratic divisor problem and applies Watt's theorem to analyze the twisted fourth moment of the zeta-function.

Findings

Extended the length of Dirichlet polynomials considered from T^{1/11} to T^{1/4}

Provided applications to zeros of the zeta-function and moment bounds

Simplified combinatorics of main terms using Watt's theorem

Abstract

We estimate asymptotically the fourth moment of the Riemann zeta-function twisted by a Dirichlet polynomial of length $T^{\frac14 - \varepsilon}$. Our work relies crucially on Watt's theorem on averages of Kloosterman fractions. In the context of the twisted fourth moment, Watt's result is an optimal replacement for Selberg's eigenvalue conjecture. Our work extends the previous result of Hughes and Young, where Dirichlet polynomials of length $T^{\frac{1}{11}-\varepsilon}$ were considered. Our result has several applications, among others to the proportion of critical zeros of the Riemann zeta-function, zero spacing and lower bounds for moments. Along the way we obtain an asymptotic formula for a quadratic divisor problem, where the condition $a m_1 m_2 - b n_1 n_2 = h$ is summed with smooth averaging on the variables $m_1, m_2, n_1, n_2, h$ and arbitrary weights in the average on $a,b$. Using Watt's work allows us to exploit all averages simultaneously. It turns out that averaging over $m_1, m_2, n_1, n_2, h$ right away in the quadratic divisor problem simplifies considerably the combinatorics of the main terms in the twisted fourth moment.