Sums of Kloosterman sums over primes in an arithmetic progression

TL;DR

This paper estimates sums of Kloosterman sums over primes in arithmetic progressions, extending previous results on cancellation in sums of Kloosterman sums over primes, using advanced bilinear form bounds and oscillatory integral asymptotics.

Contribution

It introduces a novel optimization method comparing three bounds for bilinear forms involving Kloosterman sums, including new uniform asymptotics and stationary phase analysis.

Findings

Achieves cancellation estimates for sums of Kloosterman sums over primes in arithmetic progressions.

Develops a new bilinear bound using uniform asymptotics for oscillatory integrals.

Utilizes deep existing bilinear bounds to improve analysis of Kloosterman sum sums.

Abstract

For $q$ prime, $X \geq 1$ and coprime $u,v \in \mathbb{N}$ we estimate the sums \begin{equation*} \sum_{\substack{p \leq X \substack p \equiv u \hspace{-0.25cm} \mod{v} p \text{ prime}}} \text{Kl}_2(p;q), \end{equation*} where $\text{Kl}_2(p;q)$ denotes a normalised Kloosterman sum with modulus $q$. This is a sparse analogue of a recent theorem due to Blomer, Fouvry, Kowalski, Michel and Mili\'cevi\'c showing cancellation amongst sums of Kloosterman sums over primes in short intervals. We use an optimisation argument inspired by Fouvry, Kowalski and Michel. Our argument compares three different bounds for bilinear forms involving Kloosterman sums. The first input in this method is a bilinear bound we prove using uniform asymptotics for oscillatory integrals due to Kiral, Petrow and Young. In contrast with the case when the sum runs over all primes, we exploit cancellation over a sum of stationary phase integrals that result from a Voronoi type summation. The second and third inputs are deep bilinear bounds for Kloosterman sums due to Fouvry-Kowalski-Michel and Kowalski-Michel-Sawin.